Implement all resolution change policies for desktop and tab capture.

Prior to this change, desktop/window capture would emit frames of any
size, regardless of the resolution change policy; and tab capture would
always emit frames of a fixed resolution.  Both cause a problem where
some receivers of the captured video need to do scaling/letterboxing
themselves for proper UX, and other receivers require this be done on
by the capture pipeline.

This change builds upon https://codereview.chromium.org/1124263004,
which allows the client to specify capture constraints that configure
the capture pipeline to do (or not do) the scaling/letterboxing.  All
frame resolution calculation logic has been factored into one place in a
new CaptureResolutionChooser class, which also depends on new utility
functions added to media/base/video_util.*.

BUG=473336

Review URL: https://codereview.chromium.org/1135823004

Cr-Commit-Position: refs/heads/master@{#330232}

18 files changed, 972 insertions, 246 deletions

diff --git a/content/browser/media/capture/capture_resolution_chooser.cc b/content/browser/media/capture/capture_resolution_chooser.cc
new file mode 100644
index 0000000..698882a
--- /dev/null
+++ b/content/browser/media/capture/capture_resolution_chooser.cc
@@ -0,0 +1,120 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/media/capture/capture_resolution_chooser.h"
+
+#include "media/base/limits.h"
+#include "media/base/video_util.h"
+
+namespace content {
+
+namespace {
+
+// Compute the minimum frame size from the given |max_frame_size| and
+// |resolution_change_policy|.
+gfx::Size ComputeMinimumCaptureSize(
+    const gfx::Size& max_frame_size,
+    media::ResolutionChangePolicy resolution_change_policy) {
+  switch (resolution_change_policy) {
+    case media::RESOLUTION_POLICY_FIXED_RESOLUTION:
+      return max_frame_size;
+    case media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO: {
+      // TODO(miu): This is a place-holder until "min constraints" are plumbed-
+      // in from the MediaStream framework.  http://crbug.com/473336
+      const int kMinLines = 180;
+      if (max_frame_size.height() <= kMinLines)
+        return max_frame_size;
+      const gfx::Size result(
+          kMinLines * max_frame_size.width() / max_frame_size.height(),
+          kMinLines);
+      if (result.width() <= 0 || result.width() > media::limits::kMaxDimension)
+        return max_frame_size;
+      return result;
+    }
+    case media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT:
+      return gfx::Size(1, 1);
+    case media::RESOLUTION_POLICY_LAST:
+      break;
+  }
+  NOTREACHED();
+  return gfx::Size(1, 1);
+}
+
+// Returns |size|, unless it exceeds |max_size| or is under |min_size|.  When
+// the bounds are exceeded, computes and returns an alternate size of similar
+// aspect ratio that is within the bounds.
+gfx::Size ComputeBoundedCaptureSize(const gfx::Size& size,
+                                    const gfx::Size& min_size,
+                                    const gfx::Size& max_size) {
+  if (size.width() > max_size.width() || size.height() > max_size.height()) {
+    gfx::Size result = media::ScaleSizeToFitWithinTarget(size, max_size);
+    result.SetToMax(min_size);
+    return result;
+  } else if (size.width() < min_size.width() ||
+             size.height() < min_size.height()) {
+    gfx::Size result = media::ScaleSizeToEncompassTarget(size, min_size);
+    result.SetToMin(max_size);
+    return result;
+  } else {
+    return size;
+  }
+}
+
+}  // namespace
+
+CaptureResolutionChooser::CaptureResolutionChooser(
+    const gfx::Size& max_frame_size,
+    media::ResolutionChangePolicy resolution_change_policy)
+    : max_frame_size_(max_frame_size),
+      min_frame_size_(ComputeMinimumCaptureSize(max_frame_size,
+                                                resolution_change_policy)),
+      resolution_change_policy_(resolution_change_policy),
+      constrained_size_(max_frame_size) {
+  DCHECK_LT(0, max_frame_size_.width());
+  DCHECK_LT(0, max_frame_size_.height());
+  DCHECK_LE(min_frame_size_.width(), max_frame_size_.width());
+  DCHECK_LE(min_frame_size_.height(), max_frame_size_.height());
+
+  RecomputeCaptureSize();
+}
+
+CaptureResolutionChooser::~CaptureResolutionChooser() {}
+
+void CaptureResolutionChooser::SetSourceSize(const gfx::Size& source_size) {
+  if (source_size.IsEmpty())
+    return;
+
+  switch (resolution_change_policy_) {
+    case media::RESOLUTION_POLICY_FIXED_RESOLUTION:
+      // Source size changes do not affect the frame resolution.  Frame
+      // resolution is always fixed to |max_frame_size_|.
+      break;
+
+    case media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO:
+      constrained_size_ = ComputeBoundedCaptureSize(
+          media::PadToMatchAspectRatio(source_size, max_frame_size_),
+          min_frame_size_,
+          max_frame_size_);
+      RecomputeCaptureSize();
+      break;
+
+    case media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT:
+      constrained_size_ = ComputeBoundedCaptureSize(
+          source_size, min_frame_size_, max_frame_size_);
+      RecomputeCaptureSize();
+      break;
+
+    case media::RESOLUTION_POLICY_LAST:
+      NOTREACHED();
+  }
+}
+
+void CaptureResolutionChooser::RecomputeCaptureSize() {
+  // TODO(miu): An upcoming change will introduce the ability to find the best
+  // capture resolution, given the current capabilities of the system.
+  // http://crbug.com/156767
+  capture_size_ = constrained_size_;
+}
+
+}  // namespace content
diff --git a/content/browser/media/capture/capture_resolution_chooser.h b/content/browser/media/capture/capture_resolution_chooser.h
new file mode 100644
index 0000000..f1bda79
--- /dev/null
+++ b/content/browser/media/capture/capture_resolution_chooser.h
@@ -0,0 +1,59 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CONTENT_BROWSER_MEDIA_CAPTURE_CAPTURE_RESOLUTION_CHOOSER_H_
+#define CONTENT_BROWSER_MEDIA_CAPTURE_CAPTURE_RESOLUTION_CHOOSER_H_
+
+#include "content/common/content_export.h"
+#include "media/base/video_capture_types.h"
+#include "ui/gfx/geometry/size.h"
+
+namespace content {
+
+// Encapsulates the logic that determines the capture frame resolution based on:
+//   1. The configured maximum frame resolution and resolution change policy.
+//   2. The resolution of the source content.
+//   3. The current capabilities of the end-to-end system, in terms of the
+//      maximum number of pixels per frame.
+class CONTENT_EXPORT CaptureResolutionChooser {
+ public:
+  // media::ResolutionChangePolicy determines whether the variable frame
+  // resolutions being computed must adhere to a fixed aspect ratio or not, or
+  // that there must only be a single fixed resolution.
+  CaptureResolutionChooser(
+      const gfx::Size& max_frame_size,
+      media::ResolutionChangePolicy resolution_change_policy);
+  ~CaptureResolutionChooser();
+
+  // Returns the current capture frame resolution to use.
+  gfx::Size capture_size() const {
+    return capture_size_;
+  }
+
+  // Updates the capture size based on a change in the resolution of the source
+  // content.
+  void SetSourceSize(const gfx::Size& source_size);
+
+ private:
+  // Called after any update that requires |capture_size_| be re-computed.
+  void RecomputeCaptureSize();
+
+  // Hard constraints.
+  const gfx::Size max_frame_size_;
+  const gfx::Size min_frame_size_;  // Computed from the ctor arguments.
+
+  // Specifies the set of heuristics to use.
+  const media::ResolutionChangePolicy resolution_change_policy_;
+
+  // The capture frame resolution to use, ignoring the limitations imposed by
+  // the capability metric.
+  gfx::Size constrained_size_;
+
+  // The current computed capture frame resolution.
+  gfx::Size capture_size_;
+};
+
+}  // namespace content
+
+#endif  // CONTENT_BROWSER_MEDIA_CAPTURE_RESOLUTION_CHOOSER_H_
diff --git a/content/browser/media/capture/capture_resolution_chooser_unittest.cc b/content/browser/media/capture/capture_resolution_chooser_unittest.cc
new file mode 100644
index 0000000..d91c0ce
--- /dev/null
+++ b/content/browser/media/capture/capture_resolution_chooser_unittest.cc
@@ -0,0 +1,169 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/media/capture/capture_resolution_chooser.h"
+
+#include "base/location.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using tracked_objects::Location;
+
+namespace content {
+
+namespace {
+
+// 16:9 maximum and minimum frame sizes.
+const int kMaxFrameWidth = 3840;
+const int kMaxFrameHeight = 2160;
+const int kMinFrameWidth = 320;
+const int kMinFrameHeight = 180;
+
+// Checks whether |size| is strictly between (inclusive) |min_size| and
+// |max_size| and has the same aspect ratio as |max_size|.
+void ExpectIsWithinBoundsAndSameAspectRatio(const Location& location,
+                                            const gfx::Size& min_size,
+                                            const gfx::Size& max_size,
+                                            const gfx::Size& size) {
+  SCOPED_TRACE(::testing::Message() << "From here: " << location.ToString());
+  EXPECT_LE(min_size.width(), size.width());
+  EXPECT_LE(min_size.height(), size.height());
+  EXPECT_GE(max_size.width(), size.width());
+  EXPECT_GE(max_size.height(), size.height());
+  EXPECT_NEAR(static_cast<double>(max_size.width()) / max_size.height(),
+              static_cast<double>(size.width()) / size.height(),
+              0.01);
+}
+
+}  // namespace
+
+TEST(CaptureResolutionChooserTest,
+     FixedResolutionPolicy_CaptureSizeAlwaysFixed) {
+  const gfx::Size the_one_frame_size(kMaxFrameWidth, kMaxFrameHeight);
+  CaptureResolutionChooser chooser(the_one_frame_size,
+                                   media::RESOLUTION_POLICY_FIXED_RESOLUTION);
+  EXPECT_EQ(the_one_frame_size, chooser.capture_size());
+
+  chooser.SetSourceSize(the_one_frame_size);
+  EXPECT_EQ(the_one_frame_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth + 424, kMaxFrameHeight - 101));
+  EXPECT_EQ(the_one_frame_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth - 202, kMaxFrameHeight + 56));
+  EXPECT_EQ(the_one_frame_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMinFrameWidth, kMinFrameHeight));
+  EXPECT_EQ(the_one_frame_size, chooser.capture_size());
+}
+
+TEST(CaptureResolutionChooserTest,
+     FixedAspectRatioPolicy_CaptureSizeHasSameAspectRatio) {
+  CaptureResolutionChooser chooser(
+      gfx::Size(kMaxFrameWidth, kMaxFrameHeight),
+      media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO);
+
+  // Starting condition.
+  const gfx::Size min_size(kMinFrameWidth, kMinFrameHeight);
+  const gfx::Size max_size(kMaxFrameWidth, kMaxFrameHeight);
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  // Max size in --> max size out.
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth, kMaxFrameHeight));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  // Various source sizes within bounds.
+  chooser.SetSourceSize(gfx::Size(640, 480));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(480, 640));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(640, 640));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  // Bad source size results in no update.
+  const gfx::Size unchanged_size = chooser.capture_size();
+  chooser.SetSourceSize(gfx::Size(0, 0));
+  EXPECT_EQ(unchanged_size, chooser.capture_size());
+
+  // Downscaling size (preserving aspect ratio) when source size exceeds the
+  // upper bounds.
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth * 2, kMaxFrameHeight * 2));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth * 2, kMaxFrameHeight));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth, kMaxFrameHeight * 2));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  // Upscaling size (preserving aspect ratio) when source size is under the
+  // lower bounds.
+  chooser.SetSourceSize(gfx::Size(kMinFrameWidth / 2, kMinFrameHeight / 2));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMinFrameWidth / 2, kMaxFrameHeight));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMinFrameWidth, kMinFrameHeight / 2));
+  ExpectIsWithinBoundsAndSameAspectRatio(
+      FROM_HERE, min_size, max_size, chooser.capture_size());
+}
+
+TEST(CaptureResolutionChooserTest,
+     AnyWithinLimitPolicy_CaptureSizeIsAnythingWithinLimits) {
+  const gfx::Size max_size(kMaxFrameWidth, kMaxFrameHeight);
+  CaptureResolutionChooser chooser(
+      max_size, media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT);
+
+  // Starting condition.
+  EXPECT_EQ(max_size, chooser.capture_size());
+
+  // Max size in --> max size out.
+  chooser.SetSourceSize(max_size);
+  EXPECT_EQ(max_size, chooser.capture_size());
+
+  // Various source sizes within bounds.
+  chooser.SetSourceSize(gfx::Size(640, 480));
+  EXPECT_EQ(gfx::Size(640, 480), chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(480, 640));
+  EXPECT_EQ(gfx::Size(480, 640), chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(640, 640));
+  EXPECT_EQ(gfx::Size(640, 640), chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(2, 2));
+  EXPECT_EQ(gfx::Size(2, 2), chooser.capture_size());
+
+  // Bad source size results in no update.
+  const gfx::Size unchanged_size = chooser.capture_size();
+  chooser.SetSourceSize(gfx::Size(0, 0));
+  EXPECT_EQ(unchanged_size, chooser.capture_size());
+
+  // Downscaling size (preserving aspect ratio) when source size exceeds the
+  // upper bounds.
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth * 2, kMaxFrameHeight * 2));
+  EXPECT_EQ(max_size, chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth * 2, kMaxFrameHeight));
+  EXPECT_EQ(gfx::Size(kMaxFrameWidth, kMaxFrameHeight / 2),
+            chooser.capture_size());
+
+  chooser.SetSourceSize(gfx::Size(kMaxFrameWidth, kMaxFrameHeight * 2));
+  EXPECT_EQ(gfx::Size(kMaxFrameWidth / 2, kMaxFrameHeight),
+            chooser.capture_size());
+}
+
+}  // namespace content
diff --git a/content/browser/media/capture/content_video_capture_device_core.cc b/content/browser/media/capture/content_video_capture_device_core.cc
index 8d44104..da0862c 100644
--- a/content/browser/media/capture/content_video_capture_device_core.cc
+++ b/content/browser/media/capture/content_video_capture_device_core.cc
@@ -49,7 +49,9 @@ ThreadSafeCaptureOracle::ThreadSafeCaptureOracle(
       oracle_(base::TimeDelta::FromMicroseconds(
           static_cast<int64>(1000000.0 / params.requested_format.frame_rate +
                              0.5 /* to round to nearest int */))),
-      params_(params) {}
+      params_(params),
+      resolution_chooser_(params.requested_format.frame_size,
+                          params.resolution_change_policy) {}
 
 ThreadSafeCaptureOracle::~ThreadSafeCaptureOracle() {}
 
@@ -67,9 +69,7 @@ bool ThreadSafeCaptureOracle::ObserveEventAndDecideCapture(
   if (!client_)
     return false;  // Capture is stopped.
 
-  if (capture_size_.IsEmpty())
-    capture_size_ = max_frame_size();
-  const gfx::Size visible_size = capture_size_;
+  const gfx::Size visible_size = resolution_chooser_.capture_size();
   // Always round up the coded size to multiple of 16 pixels.
   // See http://crbug.com/402151.
   const gfx::Size coded_size((visible_size.width() + 15) & ~15,
@@ -141,30 +141,15 @@ bool ThreadSafeCaptureOracle::ObserveEventAndDecideCapture(
 
 gfx::Size ThreadSafeCaptureOracle::GetCaptureSize() const {
   base::AutoLock guard(lock_);
-  return capture_size_.IsEmpty() ? max_frame_size() : capture_size_;
+  return resolution_chooser_.capture_size();
 }
 
 void ThreadSafeCaptureOracle::UpdateCaptureSize(const gfx::Size& source_size) {
   base::AutoLock guard(lock_);
-
-  // Update |capture_size_| based on |source_size| if either: 1) The resolution
-  // change policy specifies fixed frame sizes and |capture_size_| has not yet
-  // been set; or 2) The resolution change policy specifies dynamic frame
-  // sizes.
-  if (capture_size_.IsEmpty() || params_.resolution_change_policy ==
-      media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT) {
-    capture_size_ = source_size;
-    // The capture size should not exceed the maximum frame size.
-    if (capture_size_.width() > max_frame_size().width() ||
-        capture_size_.height() > max_frame_size().height()) {
-      capture_size_ = media::ComputeLetterboxRegion(
-          gfx::Rect(max_frame_size()), capture_size_).size();
-    }
-    // The capture size must be even and not less than the minimum frame size.
-    capture_size_ = gfx::Size(
-        std::max(kMinFrameWidth, MakeEven(capture_size_.width())),
-        std::max(kMinFrameHeight, MakeEven(capture_size_.height())));
-  }
+  resolution_chooser_.SetSourceSize(source_size);
+  VLOG(1) << "Source size changed to " << source_size.ToString()
+          << " --> Capture size is now "
+          << resolution_chooser_.capture_size().ToString();
 }
 
 void ThreadSafeCaptureOracle::Stop() {
@@ -234,23 +219,15 @@ void ContentVideoCaptureDeviceCore::AllocateAndStart(
     return;
   }
 
-   if (params.requested_format.frame_size.width() < kMinFrameWidth ||
-       params.requested_format.frame_size.height() < kMinFrameHeight) {
-     std::string error_msg =
-         "invalid frame size: " + params.requested_format.frame_size.ToString();
-     DVLOG(1) << error_msg;
-     client->OnError(error_msg);
-     return;
-   }
-
-  media::VideoCaptureParams new_params = params;
-  // Frame dimensions must each be an even integer since the client wants (or
-  // will convert to) YUV420.
-  new_params.requested_format.frame_size.SetSize(
-      MakeEven(params.requested_format.frame_size.width()),
-      MakeEven(params.requested_format.frame_size.height()));
+  if (params.requested_format.frame_size.IsEmpty()) {
+    std::string error_msg =
+        "invalid frame size: " + params.requested_format.frame_size.ToString();
+    DVLOG(1) << error_msg;
+    client->OnError(error_msg);
+    return;
+  }
 
-  oracle_proxy_ = new ThreadSafeCaptureOracle(client.Pass(), new_params);
+  oracle_proxy_ = new ThreadSafeCaptureOracle(client.Pass(), params);
 
   // Starts the capture machine asynchronously.
   BrowserThread::PostTaskAndReplyWithResult(
@@ -259,7 +236,7 @@ void ContentVideoCaptureDeviceCore::AllocateAndStart(
       base::Bind(&VideoCaptureMachine::Start,
                  base::Unretained(capture_machine_.get()),
                  oracle_proxy_,
-                 new_params),
+                 params),
       base::Bind(&ContentVideoCaptureDeviceCore::CaptureStarted, AsWeakPtr()));
 
   TransitionStateTo(kCapturing);
diff --git a/content/browser/media/capture/content_video_capture_device_core.h b/content/browser/media/capture/content_video_capture_device_core.h
index f477a15..67dffd6 100644
--- a/content/browser/media/capture/content_video_capture_device_core.h
+++ b/content/browser/media/capture/content_video_capture_device_core.h
@@ -11,6 +11,7 @@
 #include "base/memory/weak_ptr.h"
 #include "base/threading/thread.h"
 #include "base/threading/thread_checker.h"
+#include "content/browser/media/capture/capture_resolution_chooser.h"
 #include "content/browser/media/capture/video_capture_oracle.h"
 #include "content/common/content_export.h"
 #include "media/base/video_frame.h"
@@ -23,15 +24,6 @@ class VideoFrame;
 
 namespace content {
 
-const int kMinFrameWidth = 2;
-const int kMinFrameHeight = 2;
-
-// Returns the nearest even integer closer to zero.
-template<typename IntType>
-IntType MakeEven(IntType x) {
-  return x & static_cast<IntType>(-2);
-}
-
 class VideoCaptureMachine;
 
 // Thread-safe, refcounted proxy to the VideoCaptureOracle.  This proxy wraps
@@ -104,8 +96,8 @@ class ThreadSafeCaptureOracle
   // The video capture parameters used to construct the oracle proxy.
   const media::VideoCaptureParams params_;
 
-  // The current video capture size.
-  gfx::Size capture_size_;
+  // Determines video capture frame sizes.
+  CaptureResolutionChooser resolution_chooser_;
 };
 
 // Keeps track of the video capture source frames and executes copying on the
diff --git a/content/browser/media/capture/desktop_capture_device.cc b/content/browser/media/capture/desktop_capture_device.cc
index a11e473..e42a678 100644
--- a/content/browser/media/capture/desktop_capture_device.cc
+++ b/content/browser/media/capture/desktop_capture_device.cc
@@ -12,6 +12,7 @@
 #include "base/synchronization/lock.h"
 #include "base/threading/thread.h"
 #include "base/timer/timer.h"
+#include "content/browser/media/capture/capture_resolution_chooser.h"
 #include "content/browser/media/capture/desktop_capture_device_uma_types.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/desktop_media_id.h"
@@ -72,11 +73,6 @@ class DesktopCaptureDevice::Core : public webrtc::DesktopCapturer::Callback {
   webrtc::SharedMemory* CreateSharedMemory(size_t size) override;
   void OnCaptureCompleted(webrtc::DesktopFrame* frame) override;
 
-  // Chooses new output properties based on the supplied source size and the
-  // properties requested to Allocate(), and dispatches OnFrameInfo[Changed]
-  // notifications.
-  void RefreshCaptureFormat(const webrtc::DesktopSize& frame_size);
-
   // Method that is scheduled on |task_runner_| to be called on regular interval
   // to capture a frame.
   void OnCaptureTimer();
@@ -97,24 +93,20 @@ class DesktopCaptureDevice::Core : public webrtc::DesktopCapturer::Callback {
   // on the task_runner_ thread.
   scoped_ptr<Client> client_;
 
-  // Requested video capture format (width, height, frame rate, etc).
-  media::VideoCaptureParams requested_params_;
-
-  // Actual video capture format being generated.
-  media::VideoCaptureFormat capture_format_;
+  // Requested video capture frame rate.
+  float requested_frame_rate_;
 
   // Size of frame most recently captured from the source.
   webrtc::DesktopSize previous_frame_size_;
 
+  // Determines the size of frames to deliver to the |client_|.
+  scoped_ptr<CaptureResolutionChooser> resolution_chooser_;
+
   // DesktopFrame into which captured frames are down-scaled and/or letterboxed,
   // depending upon the caller's requested capture capabilities. If frames can
   // be returned to the caller directly then this is NULL.
   scoped_ptr<webrtc::DesktopFrame> output_frame_;
 
-  // Sub-rectangle of |output_frame_| into which the source will be scaled
-  // and/or letterboxed.
-  webrtc::DesktopRect output_rect_;
-
   // Timer used to capture the frame.
   base::OneShotTimer<Core> capture_timer_;
 
@@ -167,12 +159,10 @@ void DesktopCaptureDevice::Core::AllocateAndStart(
   DCHECK(!client_.get());
 
   client_ = client.Pass();
-  requested_params_ = params;
-
-  capture_format_ = requested_params_.requested_format;
-
-  // This capturer always outputs ARGB, non-interlaced.
-  capture_format_.pixel_format = media::PIXEL_FORMAT_ARGB;
+  requested_frame_rate_ = params.requested_format.frame_rate;
+  resolution_chooser_.reset(new CaptureResolutionChooser(
+      params.requested_format.frame_size,
+      params.resolution_change_policy));
 
   power_save_blocker_.reset(
       PowerSaveBlocker::Create(
@@ -238,16 +228,29 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
 
   scoped_ptr<webrtc::DesktopFrame> owned_frame(frame);
 
+  // If the frame size has changed, drop the output frame (if any), and
+  // determine the new output size.
+  if (!previous_frame_size_.equals(frame->size())) {
+    output_frame_.reset();
+    resolution_chooser_->SetSourceSize(gfx::Size(frame->size().width(),
+                                                 frame->size().height()));
+    previous_frame_size_ = frame->size();
+  }
+  // Align to 2x2 pixel boundaries, as required by OnIncomingCapturedData() so
+  // it can convert the frame to I420 format.
+  const webrtc::DesktopSize output_size(
+      resolution_chooser_->capture_size().width() & ~1,
+      resolution_chooser_->capture_size().height() & ~1);
+  if (output_size.is_empty())
+    return;
+
   // On OSX We receive a 1x1 frame when the shared window is minimized. It
   // cannot be subsampled to I420 and will be dropped downstream. So we replace
   // it with a black frame to avoid the video appearing frozen at the last
   // frame.
   if (frame->size().width() == 1 || frame->size().height() == 1) {
     if (!black_frame_.get()) {
-      black_frame_.reset(
-          new webrtc::BasicDesktopFrame(
-              webrtc::DesktopSize(capture_format_.frame_size.width(),
-                                  capture_format_.frame_size.height())));
+      black_frame_.reset(new webrtc::BasicDesktopFrame(output_size));
       memset(black_frame_->data(),
              0,
              black_frame_->stride() * black_frame_->size().height());
@@ -256,11 +259,6 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
     frame = black_frame_.get();
   }
 
-  // Handle initial frame size and size changes.
-  RefreshCaptureFormat(frame->size());
-
-  webrtc::DesktopSize output_size(capture_format_.frame_size.width(),
-                                  capture_format_.frame_size.height());
   size_t output_bytes = output_size.width() * output_size.height() *
       webrtc::DesktopFrame::kBytesPerPixel;
   const uint8_t* output_data = NULL;
@@ -270,7 +268,7 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
     // match the output size.
 
     // Allocate a buffer of the correct size to scale the frame into.
-    // |output_frame_| is cleared whenever |output_rect_| changes, so we don't
+    // |output_frame_| is cleared whenever the output size changes, so we don't
     // need to worry about clearing out stale pixel data in letterboxed areas.
     if (!output_frame_) {
       output_frame_.reset(new webrtc::BasicDesktopFrame(output_size));
@@ -280,13 +278,15 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
 
     // TODO(wez): Optimize this to scale only changed portions of the output,
     // using ARGBScaleClip().
+    const webrtc::DesktopRect output_rect =
+        ComputeLetterboxRect(output_size, frame->size());
     uint8_t* output_rect_data = output_frame_->data() +
-        output_frame_->stride() * output_rect_.top() +
-        webrtc::DesktopFrame::kBytesPerPixel * output_rect_.left();
+        output_frame_->stride() * output_rect.top() +
+        webrtc::DesktopFrame::kBytesPerPixel * output_rect.left();
     libyuv::ARGBScale(frame->data(), frame->stride(),
                       frame->size().width(), frame->size().height(),
                       output_rect_data, output_frame_->stride(),
-                      output_rect_.width(), output_rect_.height(),
+                      output_rect.width(), output_rect.height(),
                       libyuv::kFilterBilinear);
     output_data = output_frame_->data();
   } else if (IsFrameUnpackedOrInverted(frame)) {
@@ -311,49 +311,14 @@ void DesktopCaptureDevice::Core::OnCaptureCompleted(
   }
 
   client_->OnIncomingCapturedData(
-      output_data, output_bytes, capture_format_, 0, base::TimeTicks::Now());
-}
-
-void DesktopCaptureDevice::Core::RefreshCaptureFormat(
-    const webrtc::DesktopSize& frame_size) {
-  if (previous_frame_size_.equals(frame_size))
-    return;
-
-  // Clear the output frame, if any, since it will either need resizing, or
-  // clearing of stale data in letterbox areas, anyway.
-  output_frame_.reset();
-
-  if (previous_frame_size_.is_empty() ||
-      requested_params_.resolution_change_policy ==
-      media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT) {
-    // If this is the first frame, or the receiver supports variable resolution
-    // then determine the output size by treating the requested width & height
-    // as maxima.
-    if (frame_size.width() >
-            requested_params_.requested_format.frame_size.width() ||
-        frame_size.height() >
-            requested_params_.requested_format.frame_size.height()) {
-      output_rect_ = ComputeLetterboxRect(
-          webrtc::DesktopSize(
-              requested_params_.requested_format.frame_size.width(),
-              requested_params_.requested_format.frame_size.height()),
-          frame_size);
-      output_rect_.Translate(-output_rect_.left(), -output_rect_.top());
-    } else {
-      output_rect_ = webrtc::DesktopRect::MakeSize(frame_size);
-    }
-    capture_format_.frame_size.SetSize(output_rect_.width(),
-                                       output_rect_.height());
-  } else {
-    // Otherwise the output frame size cannot change, so just scale and
-    // letterbox.
-    output_rect_ = ComputeLetterboxRect(
-        webrtc::DesktopSize(capture_format_.frame_size.width(),
-                            capture_format_.frame_size.height()),
-        frame_size);
-  }
-
-  previous_frame_size_ = frame_size;
+      output_data,
+      output_bytes,
+      media::VideoCaptureFormat(gfx::Size(output_size.width(),
+                                          output_size.height()),
+                                requested_frame_rate_,
+                                media::PIXEL_FORMAT_ARGB),
+      0,
+      base::TimeTicks::Now());
 }
 
 void DesktopCaptureDevice::Core::OnCaptureTimer() {
@@ -375,7 +340,8 @@ void DesktopCaptureDevice::Core::CaptureFrameAndScheduleNext() {
   // Limit frame-rate to reduce CPU consumption.
   base::TimeDelta capture_period = std::max(
     (last_capture_duration * 100) / kMaximumCpuConsumptionPercentage,
-    base::TimeDelta::FromSeconds(1) / capture_format_.frame_rate);
+    base::TimeDelta::FromMicroseconds(static_cast<int64>(
+        1000000.0 / requested_frame_rate_ + 0.5 /* round to nearest int */)));
 
   // Schedule a task for the next frame.
   capture_timer_.Start(FROM_HERE, capture_period - last_capture_duration,
diff --git a/content/browser/media/capture/desktop_capture_device_unittest.cc b/content/browser/media/capture/desktop_capture_device_unittest.cc
index c86ddd3..56e06ff 100644
--- a/content/browser/media/capture/desktop_capture_device_unittest.cc
+++ b/content/browser/media/capture/desktop_capture_device_unittest.cc
@@ -4,6 +4,7 @@
 
 #include "content/browser/media/capture/desktop_capture_device.h"
 
+#include <algorithm>
 #include <string>
 
 #include "base/basictypes.h"
@@ -22,8 +23,10 @@ using ::testing::_;
 using ::testing::AnyNumber;
 using ::testing::DoAll;
 using ::testing::Expectation;
+using ::testing::Invoke;
 using ::testing::InvokeWithoutArgs;
 using ::testing::SaveArg;
+using ::testing::WithArg;
 
 namespace content {
 
@@ -33,10 +36,10 @@ MATCHER_P2(EqualsCaptureCapability, width, height, "") {
   return arg.width == width && arg.height == height;
 }
 
-const int kTestFrameWidth1 = 100;
-const int kTestFrameHeight1 = 100;
-const int kTestFrameWidth2 = 200;
-const int kTestFrameHeight2 = 150;
+const int kTestFrameWidth1 = 500;
+const int kTestFrameHeight1 = 500;
+const int kTestFrameWidth2 = 400;
+const int kTestFrameHeight2 = 300;
 
 const int kFrameRate = 30;
 
@@ -208,6 +211,32 @@ class FakeScreenCapturer : public webrtc::ScreenCapturer {
   bool generate_cropped_frames_;
 };
 
+// Helper used to check that only two specific frame sizes are delivered to the
+// OnIncomingCapturedData() callback.
+class FormatChecker {
+ public:
+  FormatChecker(const gfx::Size& size_for_even_frames,
+                const gfx::Size& size_for_odd_frames)
+      : size_for_even_frames_(size_for_even_frames),
+        size_for_odd_frames_(size_for_odd_frames),
+        frame_count_(0) {}
+
+  void ExpectAcceptableSize(const media::VideoCaptureFormat& format) {
+    if (frame_count_ % 2 == 0)
+      EXPECT_EQ(size_for_even_frames_, format.frame_size);
+    else
+      EXPECT_EQ(size_for_odd_frames_, format.frame_size);
+    ++frame_count_;
+    EXPECT_EQ(kFrameRate, format.frame_rate);
+    EXPECT_EQ(media::PIXEL_FORMAT_ARGB, format.pixel_format);
+  }
+
+ private:
+  const gfx::Size size_for_even_frames_;
+  const gfx::Size size_for_odd_frames_;
+  int frame_count_;
+};
+
 }  // namespace
 
 class DesktopCaptureDeviceTest : public testing::Test {
@@ -277,15 +306,15 @@ TEST_F(DesktopCaptureDeviceTest, ScreenResolutionChangeConstantResolution) {
 
   CreateScreenCaptureDevice(scoped_ptr<webrtc::DesktopCapturer>(mock_capturer));
 
-  media::VideoCaptureFormat format;
+  FormatChecker format_checker(gfx::Size(kTestFrameWidth1, kTestFrameHeight1),
+                               gfx::Size(kTestFrameWidth1, kTestFrameHeight1));
   base::WaitableEvent done_event(false, false);
-  int frame_size;
 
   scoped_ptr<MockDeviceClient> client(new MockDeviceClient());
   EXPECT_CALL(*client, OnError(_)).Times(0);
   EXPECT_CALL(*client, OnIncomingCapturedData(_, _, _, _, _)).WillRepeatedly(
-      DoAll(SaveArg<1>(&frame_size),
-            SaveArg<2>(&format),
+      DoAll(WithArg<2>(Invoke(&format_checker,
+                              &FormatChecker::ExpectAcceptableSize)),
             InvokeWithoutArgs(&done_event, &base::WaitableEvent::Signal)));
 
   media::VideoCaptureParams capture_params;
@@ -293,23 +322,66 @@ TEST_F(DesktopCaptureDeviceTest, ScreenResolutionChangeConstantResolution) {
                                                      kTestFrameHeight1);
   capture_params.requested_format.frame_rate = kFrameRate;
   capture_params.requested_format.pixel_format = media::PIXEL_FORMAT_I420;
+  capture_params.resolution_change_policy =
+      media::RESOLUTION_POLICY_FIXED_RESOLUTION;
 
   capture_device_->AllocateAndStart(capture_params, client.Pass());
 
   // Capture at least two frames, to ensure that the source frame size has
-  // changed while capturing.
-  EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
-  done_event.Reset();
-  EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
+  // changed to two different sizes while capturing.  The mock for
+  // OnIncomingCapturedData() will use FormatChecker to examine the format of
+  // each frame being delivered.
+  for (int i = 0; i < 2; ++i) {
+    EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
+    done_event.Reset();
+  }
 
   capture_device_->StopAndDeAllocate();
+}
 
-  EXPECT_EQ(kTestFrameWidth1, format.frame_size.width());
-  EXPECT_EQ(kTestFrameHeight1, format.frame_size.height());
-  EXPECT_EQ(kFrameRate, format.frame_rate);
-  EXPECT_EQ(media::PIXEL_FORMAT_ARGB, format.pixel_format);
+// Test that screen capturer behaves correctly if the source frame size changes,
+// where the video frames sent the the client vary in resolution but maintain
+// the same aspect ratio.
+TEST_F(DesktopCaptureDeviceTest, ScreenResolutionChangeFixedAspectRatio) {
+  FakeScreenCapturer* mock_capturer = new FakeScreenCapturer();
 
-  EXPECT_EQ(format.frame_size.GetArea() * 4, frame_size);
+  CreateScreenCaptureDevice(scoped_ptr<webrtc::DesktopCapturer>(mock_capturer));
+
+  FormatChecker format_checker(gfx::Size(888, 500), gfx::Size(532, 300));
+  base::WaitableEvent done_event(false, false);
+
+  scoped_ptr<MockDeviceClient> client(new MockDeviceClient());
+  EXPECT_CALL(*client, OnError(_)).Times(0);
+  EXPECT_CALL(*client, OnIncomingCapturedData(_, _, _, _, _)).WillRepeatedly(
+      DoAll(WithArg<2>(Invoke(&format_checker,
+                              &FormatChecker::ExpectAcceptableSize)),
+            InvokeWithoutArgs(&done_event, &base::WaitableEvent::Signal)));
+
+  media::VideoCaptureParams capture_params;
+  const gfx::Size high_def_16_by_9(1920, 1080);
+  ASSERT_GE(high_def_16_by_9.width(),
+            std::max(kTestFrameWidth1, kTestFrameWidth2));
+  ASSERT_GE(high_def_16_by_9.height(),
+            std::max(kTestFrameHeight1, kTestFrameHeight2));
+  capture_params.requested_format.frame_size = high_def_16_by_9;
+  capture_params.requested_format.frame_rate = kFrameRate;
+  capture_params.requested_format.pixel_format = media::PIXEL_FORMAT_I420;
+  capture_params.resolution_change_policy =
+      media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO;
+
+  capture_device_->AllocateAndStart(
+      capture_params, client.Pass());
+
+  // Capture at least three frames, to ensure that the source frame size has
+  // changed to two different sizes while capturing.  The mock for
+  // OnIncomingCapturedData() will use FormatChecker to examine the format of
+  // each frame being delivered.
+  for (int i = 0; i < 3; ++i) {
+    EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
+    done_event.Reset();
+  }
+
+  capture_device_->StopAndDeAllocate();
 }
 
 // Test that screen capturer behaves correctly if the source frame size changes
@@ -319,38 +391,42 @@ TEST_F(DesktopCaptureDeviceTest, ScreenResolutionChangeVariableResolution) {
 
   CreateScreenCaptureDevice(scoped_ptr<webrtc::DesktopCapturer>(mock_capturer));
 
-  media::VideoCaptureFormat format;
+  FormatChecker format_checker(gfx::Size(kTestFrameWidth1, kTestFrameHeight1),
+                               gfx::Size(kTestFrameWidth2, kTestFrameHeight2));
   base::WaitableEvent done_event(false, false);
 
   scoped_ptr<MockDeviceClient> client(new MockDeviceClient());
   EXPECT_CALL(*client, OnError(_)).Times(0);
   EXPECT_CALL(*client, OnIncomingCapturedData(_, _, _, _, _)).WillRepeatedly(
-      DoAll(SaveArg<2>(&format),
+      DoAll(WithArg<2>(Invoke(&format_checker,
+                              &FormatChecker::ExpectAcceptableSize)),
             InvokeWithoutArgs(&done_event, &base::WaitableEvent::Signal)));
 
   media::VideoCaptureParams capture_params;
-  capture_params.requested_format.frame_size.SetSize(kTestFrameWidth2,
-                                                     kTestFrameHeight2);
+  const gfx::Size high_def_16_by_9(1920, 1080);
+  ASSERT_GE(high_def_16_by_9.width(),
+            std::max(kTestFrameWidth1, kTestFrameWidth2));
+  ASSERT_GE(high_def_16_by_9.height(),
+            std::max(kTestFrameHeight1, kTestFrameHeight2));
+  capture_params.requested_format.frame_size = high_def_16_by_9;
   capture_params.requested_format.frame_rate = kFrameRate;
   capture_params.requested_format.pixel_format = media::PIXEL_FORMAT_I420;
+  capture_params.resolution_change_policy =
+      media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT;
 
   capture_device_->AllocateAndStart(
       capture_params, client.Pass());
 
   // Capture at least three frames, to ensure that the source frame size has
-  // changed at least twice while capturing.
-  EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
-  done_event.Reset();
-  EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
-  done_event.Reset();
-  EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
+  // changed to two different sizes while capturing.  The mock for
+  // OnIncomingCapturedData() will use FormatChecker to examine the format of
+  // each frame being delivered.
+  for (int i = 0; i < 3; ++i) {
+    EXPECT_TRUE(done_event.TimedWait(TestTimeouts::action_max_timeout()));
+    done_event.Reset();
+  }
 
   capture_device_->StopAndDeAllocate();
-
-  EXPECT_EQ(kTestFrameWidth1, format.frame_size.width());
-  EXPECT_EQ(kTestFrameHeight1, format.frame_size.height());
-  EXPECT_EQ(kFrameRate, format.frame_rate);
-  EXPECT_EQ(media::PIXEL_FORMAT_ARGB, format.pixel_format);
 }
 
 // This test verifies that an unpacked frame is converted to a packed frame.
diff --git a/content/browser/media/capture/web_contents_audio_input_stream.cc b/content/browser/media/capture/web_contents_audio_input_stream.cc
index 629d106..8fd1f97 100644
--- a/content/browser/media/capture/web_contents_audio_input_stream.cc
+++ b/content/browser/media/capture/web_contents_audio_input_stream.cc
@@ -91,7 +91,7 @@ class WebContentsAudioInputStream::Impl
 
   // Called by WebContentsTracker when the target of the audio mirroring has
   // changed.
-  void OnTargetChanged(RenderWidgetHost* target);
+  void OnTargetChanged(bool had_target);
 
   // Injected dependencies.
   const int initial_render_process_id_;
@@ -305,11 +305,10 @@ void WebContentsAudioInputStream::Impl::ReleaseInput(
   delete stream;
 }
 
-void WebContentsAudioInputStream::Impl::OnTargetChanged(
-    RenderWidgetHost* target) {
+void WebContentsAudioInputStream::Impl::OnTargetChanged(bool had_target) {
   DCHECK(thread_checker_.CalledOnValidThread());
 
-  is_target_lost_ = !target;
+  is_target_lost_ = !had_target;
 
   if (state_ == MIRRORING) {
     if (is_target_lost_) {
diff --git a/content/browser/media/capture/web_contents_audio_input_stream_unittest.cc b/content/browser/media/capture/web_contents_audio_input_stream_unittest.cc
index ffe8b4b..0eebd7a 100644
--- a/content/browser/media/capture/web_contents_audio_input_stream_unittest.cc
+++ b/content/browser/media/capture/web_contents_audio_input_stream_unittest.cc
@@ -356,13 +356,7 @@ class WebContentsAudioInputStreamTest : public testing::Test {
  private:
   void SimulateChangeCallback(int render_process_id, int render_frame_id) {
     ASSERT_FALSE(change_callback_.is_null());
-    if (render_process_id == -1 || render_frame_id == -1) {
-      change_callback_.Run(NULL);
-    } else {
-      // For our tests, any non-NULL value will suffice since it will not be
-      // dereferenced.
-      change_callback_.Run(reinterpret_cast<RenderWidgetHost*>(0xdeadbee5));
-    }
+    change_callback_.Run(render_process_id != -1 && render_frame_id != -1);
   }
 
   scoped_ptr<TestBrowserThreadBundle> thread_bundle_;
diff --git a/content/browser/media/capture/web_contents_tracker.cc b/content/browser/media/capture/web_contents_tracker.cc
index a9e161f..5007a58 100644
--- a/content/browser/media/capture/web_contents_tracker.cc
+++ b/content/browser/media/capture/web_contents_tracker.cc
@@ -44,6 +44,7 @@ void WebContentsTracker::Stop() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   callback_.Reset();
+  resize_callback_.Reset();
 
   if (BrowserThread::CurrentlyOn(BrowserThread::UI)) {
     WebContentsObserver::Observe(NULL);
@@ -78,6 +79,12 @@ RenderWidgetHost* WebContentsTracker::GetTargetRenderWidgetHost() const {
   return rwh;
 }
 
+void WebContentsTracker::SetResizeChangeCallback(
+    const base::Closure& callback) {
+  DCHECK(!task_runner_.get() || task_runner_->BelongsToCurrentThread());
+  resize_callback_ = callback;
+}
+
 void WebContentsTracker::OnPossibleTargetChange(bool force_callback_run) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
@@ -89,19 +96,29 @@ void WebContentsTracker::OnPossibleTargetChange(bool force_callback_run) {
   last_target_ = rwh;
 
   if (task_runner_->BelongsToCurrentThread()) {
-    MaybeDoCallback(rwh);
-  } else {
-    task_runner_->PostTask(
-        FROM_HERE,
-        base::Bind(&WebContentsTracker::MaybeDoCallback, this, rwh));
+    MaybeDoCallback(rwh != nullptr);
+    return;
   }
+
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&WebContentsTracker::MaybeDoCallback, this, rwh != nullptr));
 }
 
-void WebContentsTracker::MaybeDoCallback(RenderWidgetHost* rwh) {
+void WebContentsTracker::MaybeDoCallback(bool was_still_tracking) {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   if (!callback_.is_null())
-    callback_.Run(rwh);
+    callback_.Run(was_still_tracking);
+  if (was_still_tracking)
+    MaybeDoResizeCallback();
+}
+
+void WebContentsTracker::MaybeDoResizeCallback() {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+
+  if (!resize_callback_.is_null())
+    resize_callback_.Run();
 }
 
 void WebContentsTracker::StartObservingWebContents(int render_process_id,
@@ -128,6 +145,19 @@ void WebContentsTracker::RenderFrameHostChanged(RenderFrameHost* old_host,
   OnPossibleTargetChange(false);
 }
 
+void WebContentsTracker::MainFrameWasResized(bool width_changed) {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  if (task_runner_->BelongsToCurrentThread()) {
+    MaybeDoResizeCallback();
+    return;
+  }
+
+  task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&WebContentsTracker::MaybeDoResizeCallback, this));
+}
+
 void WebContentsTracker::WebContentsDestroyed() {
   Observe(NULL);
   OnPossibleTargetChange(false);
diff --git a/content/browser/media/capture/web_contents_tracker.h b/content/browser/media/capture/web_contents_tracker.h
index 613c971..591c5e3 100644
--- a/content/browser/media/capture/web_contents_tracker.h
+++ b/content/browser/media/capture/web_contents_tracker.h
@@ -40,15 +40,15 @@ class CONTENT_EXPORT WebContentsTracker
   explicit WebContentsTracker(bool track_fullscreen_rwh);
 
   // Callback to indicate a new RenderWidgetHost should be targeted for capture.
-  // This is also invoked with NULL to indicate tracking will not continue
+  // This is also invoked with false to indicate tracking will not continue
   // (i.e., the WebContents instance was not found or has been destroyed).
-  typedef base::Callback<void(RenderWidgetHost* rwh)> ChangeCallback;
+  typedef base::Callback<void(bool was_still_tracking)> ChangeCallback;
 
   // Start tracking.  The last-known |render_process_id| and
   // |main_render_frame_id| are provided, and |callback| will be run once to
-  // indicate the current capture target (this may occur during the invocation
-  // of Start(), or in the future).  The callback will be invoked on the same
-  // thread calling Start().
+  // indicate whether tracking successfully started (this may occur during the
+  // invocation of Start(), or in the future).  The callback will be invoked on
+  // the same thread calling Start().
   virtual void Start(int render_process_id, int main_render_frame_id,
                      const ChangeCallback& callback);
 
@@ -59,6 +59,12 @@ class CONTENT_EXPORT WebContentsTracker
   // Current target.  This must only be called on the UI BrowserThread.
   RenderWidgetHost* GetTargetRenderWidgetHost() const;
 
+  // Set a callback that is run whenever the main frame of the WebContents is
+  // resized.  This method must be called on the same thread that calls
+  // Start()/Stop(), and |callback| will be run on that same thread.  Calling
+  // the Stop() method guarantees the callback will never be invoked again.
+  void SetResizeChangeCallback(const base::Closure& callback);
+
  protected:
   friend class base::RefCountedThreadSafe<WebContentsTracker>;
   ~WebContentsTracker() override;
@@ -72,7 +78,12 @@ class CONTENT_EXPORT WebContentsTracker
 
   // Called on the thread that Start()/Stop() are called on.  Checks whether the
   // callback is still valid and, if so, runs it.
-  void MaybeDoCallback(RenderWidgetHost* rwh);
+  void MaybeDoCallback(bool was_still_tracking);
+
+  // Called on the thread that Start()/Stop() are called on.  Checks whether the
+  // callback is still valid and, if so, runs it to indicate the main frame has
+  // changed in size.
+  void MaybeDoResizeCallback();
 
   // Look-up the current WebContents instance associated with the given
   // |render_process_id| and |main_render_frame_id| and begin observing it.
@@ -86,6 +97,10 @@ class CONTENT_EXPORT WebContentsTracker
   void RenderFrameHostChanged(RenderFrameHost* old_host,
                               RenderFrameHost* new_host) override;
 
+  // WebContentsObserver override to notify the client that the source size has
+  // changed.
+  void MainFrameWasResized(bool width_changed) override;
+
   // WebContentsObserver override to notify the client that the capture target
   // has been permanently lost.
   void WebContentsDestroyed() override;
@@ -109,6 +124,9 @@ class CONTENT_EXPORT WebContentsTracker
   // This is used to eliminate duplicate callback runs.
   RenderWidgetHost* last_target_;
 
+  // Callback to run when the target RenderWidgetHost has resized.
+  base::Closure resize_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(WebContentsTracker);
 };
 
diff --git a/content/browser/media/capture/web_contents_video_capture_device.cc b/content/browser/media/capture/web_contents_video_capture_device.cc
index 8380682..292d856 100644
--- a/content/browser/media/capture/web_contents_video_capture_device.cc
+++ b/content/browser/media/capture/web_contents_video_capture_device.cc
@@ -79,7 +79,6 @@
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/display.h"
-#include "ui/gfx/geometry/size.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/screen.h"
 
@@ -87,20 +86,6 @@ namespace content {
 
 namespace {
 
-// Compute a letterbox region, aligned to even coordinates.
-gfx::Rect ComputeYV12LetterboxRegion(const gfx::Rect& visible_rect,
-                                     const gfx::Size& content_size) {
-
-  gfx::Rect result = media::ComputeLetterboxRegion(visible_rect, content_size);
-
-  result.set_x(MakeEven(result.x()));
-  result.set_y(MakeEven(result.y()));
-  result.set_width(std::max(kMinFrameWidth, MakeEven(result.width())));
-  result.set_height(std::max(kMinFrameHeight, MakeEven(result.height())));
-
-  return result;
-}
-
 void DeleteOnWorkerThread(scoped_ptr<base::Thread> render_thread,
                           const base::Closure& callback) {
   render_thread.reset();
@@ -254,8 +239,12 @@ class WebContentsCaptureMachine : public VideoCaptureMachine {
           deliver_frame_cb,
       bool success);
 
-  // Remove the old subscription, and start a new one if |rwh| is not NULL.
-  void RenewFrameSubscription(RenderWidgetHost* rwh);
+  // Remove the old subscription, and attempt to start a new one if |had_target|
+  // is true.
+  void RenewFrameSubscription(bool had_target);
+
+  // Called whenever the render widget is resized.
+  void UpdateCaptureSize();
 
   // Parameters saved in constructor.
   const int initial_render_process_id_;
@@ -396,7 +385,7 @@ void RenderVideoFrame(const SkBitmap& input,
 
   // Calculate the width and height of the content region in the |output|, based
   // on the aspect ratio of |input|.
-  gfx::Rect region_in_frame = ComputeYV12LetterboxRegion(
+  const gfx::Rect region_in_frame = media::ComputeLetterboxRegion(
       output->visible_rect(), gfx::Size(input.width(), input.height()));
 
   // Scale the bitmap to the required size, if necessary.
@@ -425,12 +414,20 @@ void RenderVideoFrame(const SkBitmap& input,
 
   TRACE_EVENT_ASYNC_STEP_INTO0("gpu.capture", "Capture", output.get(), "YUV");
   {
-    SkAutoLockPixels scaled_bitmap_locker(scaled_bitmap);
+    // Align to 2x2 pixel boundaries, as required by
+    // media::CopyRGBToVideoFrame().
+    const gfx::Rect region_in_yv12_frame(region_in_frame.x() & ~1,
+                                         region_in_frame.y() & ~1,
+                                         region_in_frame.width() & ~1,
+                                         region_in_frame.height() & ~1);
+    if (region_in_yv12_frame.IsEmpty())
+      return;
 
+    SkAutoLockPixels scaled_bitmap_locker(scaled_bitmap);
     media::CopyRGBToVideoFrame(
         reinterpret_cast<uint8*>(scaled_bitmap.getPixels()),
         scaled_bitmap.rowBytes(),
-        region_in_frame,
+        region_in_yv12_frame,
         output.get());
   }
 
@@ -501,6 +498,9 @@ bool WebContentsCaptureMachine::Start(
 
   // Note: Creation of the first WeakPtr in the following statement will cause
   // IsStarted() to return true from now on.
+  tracker_->SetResizeChangeCallback(
+      base::Bind(&WebContentsCaptureMachine::UpdateCaptureSize,
+                 weak_ptr_factory_.GetWeakPtr()));
   tracker_->Start(initial_render_process_id_, initial_main_render_frame_id_,
                   base::Bind(&WebContentsCaptureMachine::RenewFrameSubscription,
                              weak_ptr_factory_.GetWeakPtr()));
@@ -522,7 +522,7 @@ void WebContentsCaptureMachine::Stop(const base::Closure& callback) {
 
   // Note: RenewFrameSubscription() must be called before stopping |tracker_| so
   // the web_contents() can be notified that the capturing is ending.
-  RenewFrameSubscription(NULL);
+  RenewFrameSubscription(false);
   tracker_->Stop();
 
   // The render thread cannot be stopped on the UI thread, so post a message
@@ -551,11 +551,6 @@ void WebContentsCaptureMachine::Capture(
   }
 
   gfx::Size view_size = view->GetViewBounds().size();
-  gfx::Size fitted_size;
-  if (!view_size.IsEmpty()) {
-    fitted_size = ComputeYV12LetterboxRegion(target->visible_rect(),
-                                             view_size).size();
-  }
   if (view_size != last_view_size_) {
     last_view_size_ = view_size;
 
@@ -574,6 +569,8 @@ void WebContentsCaptureMachine::Capture(
                    weak_ptr_factory_.GetWeakPtr(),
                    start_time, deliver_frame_cb));
   } else {
+    const gfx::Size fitted_size = view_size.IsEmpty() ? gfx::Size() :
+        media::ComputeLetterboxRegion(target->visible_rect(), view_size).size();
     rwh->CopyFromBackingStore(
         gfx::Rect(),
         fitted_size,  // Size here is a request not always honored.
@@ -589,7 +586,10 @@ void WebContentsCaptureMachine::Capture(
 gfx::Size WebContentsCaptureMachine::ComputeOptimalTargetSize() const {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
-  gfx::Size optimal_size = oracle_proxy_->GetCaptureSize();
+  // TODO(miu): Propagate capture frame size changes as new "preferred size"
+  // updates, rather than just using the max frame size.
+  // http://crbug.com/350491
+  gfx::Size optimal_size = oracle_proxy_->max_frame_size();
 
   // If the ratio between physical and logical pixels is greater than 1:1,
   // shrink |optimal_size| by that amount.  Then, when external code resizes the
@@ -657,9 +657,12 @@ void WebContentsCaptureMachine::DidCopyFromCompositingSurfaceToVideoFrame(
   deliver_frame_cb.Run(start_time, success);
 }
 
-void WebContentsCaptureMachine::RenewFrameSubscription(RenderWidgetHost* rwh) {
+void WebContentsCaptureMachine::RenewFrameSubscription(bool had_target) {
   DCHECK_CURRENTLY_ON(BrowserThread::UI);
 
+  RenderWidgetHost* const rwh =
+      had_target ? tracker_->GetTargetRenderWidgetHost() : nullptr;
+
   // Always destroy the old subscription before creating a new one.
   const bool had_subscription = !!subscription_;
   subscription_.reset();
@@ -688,6 +691,18 @@ void WebContentsCaptureMachine::RenewFrameSubscription(RenderWidgetHost* rwh) {
                  weak_ptr_factory_.GetWeakPtr())));
 }
 
+void WebContentsCaptureMachine::UpdateCaptureSize() {
+  DCHECK_CURRENTLY_ON(BrowserThread::UI);
+
+  if (!oracle_proxy_)
+    return;
+  RenderWidgetHost* const rwh = tracker_->GetTargetRenderWidgetHost();
+  RenderWidgetHostView* const view = rwh ? rwh->GetView() : nullptr;
+  if (!view)
+    return;
+  oracle_proxy_->UpdateCaptureSize(view->GetViewBounds().size());
+}
+
 }  // namespace
 
 WebContentsVideoCaptureDevice::WebContentsVideoCaptureDevice(
diff --git a/content/browser/media/capture/web_contents_video_capture_device_unittest.cc b/content/browser/media/capture/web_contents_video_capture_device_unittest.cc
index ab430a7..02b297f 100644
--- a/content/browser/media/capture/web_contents_video_capture_device_unittest.cc
+++ b/content/browser/media/capture/web_contents_video_capture_device_unittest.cc
@@ -11,11 +11,13 @@
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "content/browser/browser_thread_impl.h"
+#include "content/browser/frame_host/render_frame_host_impl.h"
 #include "content/browser/media/capture/video_capture_oracle.h"
 #include "content/browser/media/capture/web_contents_capture_util.h"
 #include "content/browser/renderer_host/media/video_capture_buffer_pool.h"
 #include "content/browser/renderer_host/render_view_host_factory.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
+#include "content/browser/web_contents/web_contents_impl.h"
 #include "content/public/browser/notification_service.h"
 #include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_widget_host_view_frame_subscriber.h"
@@ -77,7 +79,6 @@ SkColor ConvertRgbToYuv(SkColor rgb) {
 // counted.
 class CaptureTestSourceController {
  public:
-
   CaptureTestSourceController()
       : color_(SK_ColorMAGENTA),
         copy_result_size_(kTestWidth, kTestHeight),
@@ -162,13 +163,22 @@ class CaptureTestView : public TestRenderWidgetHostView {
   explicit CaptureTestView(RenderWidgetHostImpl* rwh,
                            CaptureTestSourceController* controller)
       : TestRenderWidgetHostView(rwh),
-        controller_(controller) {}
+        controller_(controller),
+        fake_bounds_(100, 100, 100 + kTestWidth, 100 + kTestHeight) {}
 
   ~CaptureTestView() override {}
 
   // TestRenderWidgetHostView overrides.
   gfx::Rect GetViewBounds() const override {
-    return gfx::Rect(100, 100, 100 + kTestWidth, 100 + kTestHeight);
+    return fake_bounds_;
+  }
+
+  void SetSize(const gfx::Size& size) override {
+    SetBounds(gfx::Rect(fake_bounds_.origin(), size));
+  }
+
+  void SetBounds(const gfx::Rect& rect) override {
+    fake_bounds_ = rect;
   }
 
   bool CanCopyToVideoFrame() const override {
@@ -213,6 +223,7 @@ class CaptureTestView : public TestRenderWidgetHostView {
  private:
   scoped_ptr<RenderWidgetHostViewFrameSubscriber> subscriber_;
   CaptureTestSourceController* const controller_;
+  gfx::Rect fake_bounds_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(CaptureTestView);
 };
@@ -308,9 +319,10 @@ class CaptureTestRenderViewHostFactory : public RenderViewHostFactory {
 // WebContentsVideoCaptureDevice.
 class StubClient : public media::VideoCaptureDevice::Client {
  public:
-  StubClient(const base::Callback<void(SkColor)>& color_callback,
-             const base::Closure& error_callback)
-      : color_callback_(color_callback),
+  StubClient(
+      const base::Callback<void(SkColor, const gfx::Size&)>& report_callback,
+      const base::Closure& error_callback)
+      : report_callback_(report_callback),
         error_callback_(error_callback) {
     buffer_pool_ = new VideoCaptureBufferPool(2);
   }
@@ -360,20 +372,29 @@ class StubClient : public media::VideoCaptureDevice::Client {
       scoped_ptr<Buffer> buffer,
       const scoped_refptr<media::VideoFrame>& frame,
       const base::TimeTicks& timestamp) override {
-    EXPECT_EQ(gfx::Size(kTestWidth, kTestHeight), frame->visible_rect().size());
+    EXPECT_FALSE(frame->visible_rect().IsEmpty());
     EXPECT_EQ(media::VideoFrame::I420, frame->format());
     double frame_rate = 0;
     EXPECT_TRUE(
         frame->metadata()->GetDouble(media::VideoFrameMetadata::FRAME_RATE,
                                      &frame_rate));
     EXPECT_EQ(kTestFramesPerSecond, frame_rate);
-    uint8 yuv[3];
-    for (int plane = 0; plane < 3; ++plane)
-      yuv[plane] = frame->visible_data(plane)[0];
-    // TODO(nick): We just look at the first pixel presently, because if
-    // the analysis is too slow, the backlog of frames will grow without bound
-    // and trouble erupts. http://crbug.com/174519
-    color_callback_.Run((SkColorSetRGB(yuv[0], yuv[1], yuv[2])));
+
+    // TODO(miu): We just look at the center pixel presently, because if the
+    // analysis is too slow, the backlog of frames will grow without bound and
+    // trouble erupts. http://crbug.com/174519
+    using media::VideoFrame;
+    const gfx::Point center = frame->visible_rect().CenterPoint();
+    const int center_offset_y =
+        (frame->stride(VideoFrame::kYPlane) * center.y()) + center.x();
+    const int center_offset_uv =
+        (frame->stride(VideoFrame::kUPlane) * (center.y() / 2)) +
+            (center.x() / 2);
+    report_callback_.Run(
+        SkColorSetRGB(frame->data(VideoFrame::kYPlane)[center_offset_y],
+                      frame->data(VideoFrame::kUPlane)[center_offset_uv],
+                      frame->data(VideoFrame::kVPlane)[center_offset_uv]),
+        frame->visible_rect().size());
   }
 
   void OnError(const std::string& reason) override { error_callback_.Run(); }
@@ -407,7 +428,7 @@ class StubClient : public media::VideoCaptureDevice::Client {
   };
 
   scoped_refptr<VideoCaptureBufferPool> buffer_pool_;
-  base::Callback<void(SkColor)> color_callback_;
+  base::Callback<void(SkColor, const gfx::Size&)> report_callback_;
   base::Closure error_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(StubClient);
@@ -417,9 +438,11 @@ class StubClientObserver {
  public:
   StubClientObserver()
       : error_encountered_(false),
-        wait_color_yuv_(0xcafe1950) {
+        wait_color_yuv_(0xcafe1950),
+        wait_size_(kTestWidth, kTestHeight) {
     client_.reset(new StubClient(
-        base::Bind(&StubClientObserver::OnColor, base::Unretained(this)),
+        base::Bind(&StubClientObserver::DidDeliverFrame,
+                   base::Unretained(this)),
         base::Bind(&StubClientObserver::OnError, base::Unretained(this))));
   }
 
@@ -429,16 +452,30 @@ class StubClientObserver {
     return client_.Pass();
   }
 
-  void QuitIfConditionMet(SkColor color) {
+  void QuitIfConditionsMet(SkColor color, const gfx::Size& size) {
     base::AutoLock guard(lock_);
-    if (wait_color_yuv_ == color || error_encountered_)
+    if (error_encountered_)
+      base::MessageLoop::current()->Quit();
+    else if (wait_color_yuv_ == color && wait_size_.IsEmpty())
+      base::MessageLoop::current()->Quit();
+    else if (wait_color_yuv_ == color && wait_size_ == size)
       base::MessageLoop::current()->Quit();
   }
 
+  // Run the current loop until a frame is delivered with the |expected_color|
+  // and any non-empty frame size.
   void WaitForNextColor(SkColor expected_color) {
+    WaitForNextColorAndFrameSize(expected_color, gfx::Size());
+  }
+
+  // Run the current loop until a frame is delivered with the |expected_color|
+  // and is of the |expected_size|.
+  void WaitForNextColorAndFrameSize(SkColor expected_color,
+                                    const gfx::Size& expected_size) {
     {
       base::AutoLock guard(lock_);
       wait_color_yuv_ = ConvertRgbToYuv(expected_color);
+      wait_size_ = expected_size;
       error_encountered_ = false;
     }
     RunCurrentLoopWithDeadline();
@@ -452,6 +489,7 @@ class StubClientObserver {
     {
       base::AutoLock guard(lock_);
       wait_color_yuv_ = kNotInterested;
+      wait_size_ = gfx::Size();
       error_encountered_ = false;
     }
     RunCurrentLoopWithDeadline();
@@ -472,22 +510,25 @@ class StubClientObserver {
       error_encountered_ = true;
     }
     BrowserThread::PostTask(BrowserThread::UI, FROM_HERE, base::Bind(
-        &StubClientObserver::QuitIfConditionMet,
+        &StubClientObserver::QuitIfConditionsMet,
         base::Unretained(this),
-        kNothingYet));
+        kNothingYet,
+        gfx::Size()));
   }
 
-  void OnColor(SkColor color) {
+  void DidDeliverFrame(SkColor color, const gfx::Size& size) {
     BrowserThread::PostTask(BrowserThread::UI, FROM_HERE, base::Bind(
-        &StubClientObserver::QuitIfConditionMet,
+        &StubClientObserver::QuitIfConditionsMet,
         base::Unretained(this),
-        color));
+        color,
+        size));
   }
 
  private:
   base::Lock lock_;
   bool error_encountered_;
   SkColor wait_color_yuv_;
+  gfx::Size wait_size_;
   scoped_ptr<StubClient> client_;
 
   DISALLOW_COPY_AND_ASSIGN(StubClientObserver);
@@ -622,6 +663,22 @@ class WebContentsVideoCaptureDeviceTest : public testing::Test {
     }
   }
 
+  void SimulateSourceSizeChange(const gfx::Size& size) {
+    DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+    CaptureTestView* test_view = static_cast<CaptureTestView*>(
+        web_contents_->GetRenderViewHost()->GetView());
+    test_view->SetSize(size);
+    // Normally, RenderWidgetHostImpl would notify WebContentsImpl that the size
+    // has changed.  However, in this test setup where there is no render
+    // process, we must notify WebContentsImpl directly.
+    WebContentsImpl* const as_web_contents_impl =
+        static_cast<WebContentsImpl*>(web_contents_.get());
+    RenderWidgetHostDelegate* const as_rwh_delegate =
+        static_cast<RenderWidgetHostDelegate*>(as_web_contents_impl);
+    as_rwh_delegate->RenderWidgetWasResized(
+        as_web_contents_impl->GetMainFrame()->GetRenderWidgetHost(), true);
+  }
+
   void DestroyVideoCaptureDevice() { device_.reset(); }
 
   StubClientObserver* client_observer() {
@@ -879,5 +936,158 @@ TEST_F(WebContentsVideoCaptureDeviceTest, BadFramesGoodFrames) {
   device()->StopAndDeAllocate();
 }
 
+// Tests that, when configured with the FIXED_ASPECT_RATIO resolution change
+// policy, the source size changes result in video frames of possibly varying
+// resolutions, but all with the same aspect ratio.
+TEST_F(WebContentsVideoCaptureDeviceTest, VariableResolution_FixedAspectRatio) {
+  media::VideoCaptureParams capture_params;
+  capture_params.requested_format.frame_size.SetSize(kTestWidth, kTestHeight);
+  capture_params.requested_format.frame_rate = kTestFramesPerSecond;
+  capture_params.requested_format.pixel_format = media::PIXEL_FORMAT_I420;
+  capture_params.resolution_change_policy =
+      media::RESOLUTION_POLICY_FIXED_ASPECT_RATIO;
+
+  device()->AllocateAndStart(capture_params, client_observer()->PassClient());
+
+  for (int i = 0; i < 6; i++) {
+    const char* name = NULL;
+    switch (i % 3) {
+      case 0:
+        source()->SetCanCopyToVideoFrame(true);
+        source()->SetUseFrameSubscriber(false);
+        name = "VideoFrame";
+        break;
+      case 1:
+        source()->SetCanCopyToVideoFrame(false);
+        source()->SetUseFrameSubscriber(true);
+        name = "Subscriber";
+        break;
+      case 2:
+        source()->SetCanCopyToVideoFrame(false);
+        source()->SetUseFrameSubscriber(false);
+        name = "SkBitmap";
+        break;
+      default:
+        FAIL();
+    }
+
+    SCOPED_TRACE(base::StringPrintf("Using %s path, iteration #%d", name, i));
+
+    // Source size equals maximum size.  Expect delivered frames to be
+    // kTestWidth by kTestHeight.
+    source()->SetSolidColor(SK_ColorRED);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth, kTestHeight));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorRED, gfx::Size(kTestWidth, kTestHeight)));
+
+    // Source size is half in both dimensions.  Expect delivered frames to be of
+    // the same aspect ratio as kTestWidth by kTestHeight, but larger than the
+    // half size because the minimum height is 180 lines.
+    source()->SetSolidColor(SK_ColorGREEN);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth / 2, kTestHeight / 2));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorGREEN, gfx::Size(180 * kTestWidth / kTestHeight, 180)));
+
+    // Source size changes aspect ratio.  Expect delivered frames to be padded
+    // in the horizontal dimension to preserve aspect ratio.
+    source()->SetSolidColor(SK_ColorBLUE);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth / 2, kTestHeight));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorBLUE, gfx::Size(kTestWidth, kTestHeight)));
+
+    // Source size changes aspect ratio again.  Expect delivered frames to be
+    // padded in the vertical dimension to preserve aspect ratio.
+    source()->SetSolidColor(SK_ColorBLACK);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth, kTestHeight / 2));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorBLACK, gfx::Size(kTestWidth, kTestHeight)));
+  }
+
+  device()->StopAndDeAllocate();
+}
+
+// Tests that, when configured with the ANY_WITHIN_LIMIT resolution change
+// policy, the source size changes result in video frames of possibly varying
+// resolutions.
+TEST_F(WebContentsVideoCaptureDeviceTest, VariableResolution_AnyWithinLimits) {
+  media::VideoCaptureParams capture_params;
+  capture_params.requested_format.frame_size.SetSize(kTestWidth, kTestHeight);
+  capture_params.requested_format.frame_rate = kTestFramesPerSecond;
+  capture_params.requested_format.pixel_format = media::PIXEL_FORMAT_I420;
+  capture_params.resolution_change_policy =
+      media::RESOLUTION_POLICY_ANY_WITHIN_LIMIT;
+
+  device()->AllocateAndStart(capture_params, client_observer()->PassClient());
+
+  for (int i = 0; i < 6; i++) {
+    const char* name = NULL;
+    switch (i % 3) {
+      case 0:
+        source()->SetCanCopyToVideoFrame(true);
+        source()->SetUseFrameSubscriber(false);
+        name = "VideoFrame";
+        break;
+      case 1:
+        source()->SetCanCopyToVideoFrame(false);
+        source()->SetUseFrameSubscriber(true);
+        name = "Subscriber";
+        break;
+      case 2:
+        source()->SetCanCopyToVideoFrame(false);
+        source()->SetUseFrameSubscriber(false);
+        name = "SkBitmap";
+        break;
+      default:
+        FAIL();
+    }
+
+    SCOPED_TRACE(base::StringPrintf("Using %s path, iteration #%d", name, i));
+
+    // Source size equals maximum size.  Expect delivered frames to be
+    // kTestWidth by kTestHeight.
+    source()->SetSolidColor(SK_ColorRED);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth, kTestHeight));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorRED, gfx::Size(kTestWidth, kTestHeight)));
+
+    // Source size is half in both dimensions.  Expect delivered frames to also
+    // be half in both dimensions.
+    source()->SetSolidColor(SK_ColorGREEN);
+    SimulateSourceSizeChange(gfx::Size(kTestWidth / 2, kTestHeight / 2));
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorGREEN, gfx::Size(kTestWidth / 2, kTestHeight / 2)));
+
+    // Source size changes to something arbitrary.  Since the source size is
+    // less than the maximum size, expect delivered frames to be the same size
+    // as the source size.
+    source()->SetSolidColor(SK_ColorBLUE);
+    gfx::Size arbitrary_source_size(kTestWidth / 2 + 42, kTestHeight - 10);
+    SimulateSourceSizeChange(arbitrary_source_size);
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorBLUE, arbitrary_source_size));
+
+    // Source size changes to something arbitrary that exceeds the maximum frame
+    // size.  Since the source size exceeds the maximum size, expect delivered
+    // frames to be downscaled.
+    source()->SetSolidColor(SK_ColorBLACK);
+    arbitrary_source_size = gfx::Size(kTestWidth * 2 + 99, kTestHeight / 2);
+    SimulateSourceSizeChange(arbitrary_source_size);
+    SimulateDrawEvent();
+    ASSERT_NO_FATAL_FAILURE(client_observer()->WaitForNextColorAndFrameSize(
+        SK_ColorBLACK, gfx::Size(kTestWidth,
+                                 kTestWidth * arbitrary_source_size.height() /
+                                     arbitrary_source_size.width())));
+  }
+
+  device()->StopAndDeAllocate();
+}
+
 }  // namespace
 }  // namespace content
diff --git a/content/content_browser.gypi b/content/content_browser.gypi
index 6f563ce..9ae48ee8 100644
--- a/content/content_browser.gypi
+++ b/content/content_browser.gypi
@@ -973,6 +973,8 @@
       'browser/media/capture/animated_content_sampler.h',
       'browser/media/capture/audio_mirroring_manager.cc',
       'browser/media/capture/audio_mirroring_manager.h',
+      'browser/media/capture/capture_resolution_chooser.cc',
+      'browser/media/capture/capture_resolution_chooser.h',
       'browser/media/capture/content_video_capture_device_core.cc',
       'browser/media/capture/content_video_capture_device_core.h',
       'browser/media/capture/feedback_signal_accumulator.cc',
diff --git a/content/content_tests.gypi b/content/content_tests.gypi
index 188141a..86ac1d2 100644
--- a/content/content_tests.gypi
+++ b/content/content_tests.gypi
@@ -471,6 +471,7 @@
       'browser/media/audio_stream_monitor_unittest.cc',
       'browser/media/capture/animated_content_sampler_unittest.cc',
       'browser/media/capture/audio_mirroring_manager_unittest.cc',
+      'browser/media/capture/capture_resolution_chooser_unittest.cc',
       'browser/media/capture/feedback_signal_accumulator_unittest.cc',
       'browser/media/capture/smooth_event_sampler_unittest.cc',
       'browser/media/capture/video_capture_oracle_unittest.cc',
diff --git a/media/base/video_util.cc b/media/base/video_util.cc
index d794674..e04a5a3 100644
--- a/media/base/video_util.cc
+++ b/media/base/video_util.cc
@@ -270,6 +270,23 @@ void RotatePlaneByPixels(
   }
 }
 
+// Common logic for the letterboxing and scale-within/scale-encompassing
+// functions.  Scales |size| to either fit within or encompass |target|,
+// depending on whether |fit_within_target| is true.
+static gfx::Size ScaleSizeToTarget(const gfx::Size& size,
+                                   const gfx::Size& target,
+                                   bool fit_within_target) {
+  if (size.IsEmpty())
+    return gfx::Size();  // Corner case: Aspect ratio is undefined.
+
+  const int64 x = static_cast<int64>(size.width()) * target.height();
+  const int64 y = static_cast<int64>(size.height()) * target.width();
+  const bool use_target_width = fit_within_target ? (y < x) : (x < y);
+  return use_target_width ?
+      gfx::Size(target.width(), static_cast<int>(y / size.width())) :
+      gfx::Size(static_cast<int>(x / size.height()), target.height());
+}
+
 gfx::Rect ComputeLetterboxRegion(const gfx::Rect& bounds,
                                  const gfx::Size& content) {
   // If |content| has an undefined aspect ratio, let's not try to divide by
@@ -277,19 +294,33 @@ gfx::Rect ComputeLetterboxRegion(const gfx::Rect& bounds,
   if (content.IsEmpty())
     return gfx::Rect();
 
-  int64 x = static_cast<int64>(content.width()) * bounds.height();
-  int64 y = static_cast<int64>(content.height()) * bounds.width();
-
-  gfx::Size letterbox(bounds.width(), bounds.height());
-  if (y < x)
-    letterbox.set_height(static_cast<int>(y / content.width()));
-  else
-    letterbox.set_width(static_cast<int>(x / content.height()));
   gfx::Rect result = bounds;
-  result.ClampToCenteredSize(letterbox);
+  result.ClampToCenteredSize(ScaleSizeToTarget(content, bounds.size(), true));
   return result;
 }
 
+gfx::Size ScaleSizeToFitWithinTarget(const gfx::Size& size,
+                                     const gfx::Size& target) {
+  return ScaleSizeToTarget(size, target, true);
+}
+
+gfx::Size ScaleSizeToEncompassTarget(const gfx::Size& size,
+                                     const gfx::Size& target) {
+  return ScaleSizeToTarget(size, target, false);
+}
+
+gfx::Size PadToMatchAspectRatio(const gfx::Size& size,
+                                const gfx::Size& target) {
+  if (target.IsEmpty())
+    return gfx::Size();  // Aspect ratio is undefined.
+
+  const int64 x = static_cast<int64>(size.width()) * target.height();
+  const int64 y = static_cast<int64>(size.height()) * target.width();
+  if (x < y)
+    return gfx::Size(static_cast<int>(y / target.height()), size.height());
+  return gfx::Size(size.width(), static_cast<int>(x / target.width()));
+}
+
 void CopyRGBToVideoFrame(const uint8* source,
                          int stride,
                          const gfx::Rect& region_in_frame,
diff --git a/media/base/video_util.h b/media/base/video_util.h
index 7798ebe..abbcad4 100644
--- a/media/base/video_util.h
+++ b/media/base/video_util.h
@@ -84,6 +84,29 @@ MEDIA_EXPORT void RotatePlaneByPixels(
 MEDIA_EXPORT gfx::Rect ComputeLetterboxRegion(const gfx::Rect& bounds,
                                               const gfx::Size& content);
 
+// Return a scaled |size| whose area is less than or equal to |target|, where
+// one of its dimensions is equal to |target|'s.  The aspect ratio of |size| is
+// preserved as closely as possible.  If |size| is empty, the result will be
+// empty.
+MEDIA_EXPORT gfx::Size ScaleSizeToFitWithinTarget(const gfx::Size& size,
+                                                  const gfx::Size& target);
+
+// Return a scaled |size| whose area is greater than or equal to |target|, where
+// one of its dimensions is equal to |target|'s.  The aspect ratio of |size| is
+// preserved as closely as possible.  If |size| is empty, the result will be
+// empty.
+MEDIA_EXPORT gfx::Size ScaleSizeToEncompassTarget(const gfx::Size& size,
+                                                  const gfx::Size& target);
+
+// Returns |size| with only one of its dimensions increased such that the result
+// matches the aspect ratio of |target|.  This is different from
+// ScaleSizeToEncompassTarget() in two ways: 1) The goal is to match the aspect
+// ratio of |target| rather than that of |size|.  2) Only one of the dimensions
+// of |size| may change, and it may only be increased (padded).  If either
+// |size| or |target| is empty, the result will be empty.
+MEDIA_EXPORT gfx::Size PadToMatchAspectRatio(const gfx::Size& size,
+                                             const gfx::Size& target);
+
 // Copy an RGB bitmap into the specified |region_in_frame| of a YUV video frame.
 // Fills the regions outside |region_in_frame| with black.
 MEDIA_EXPORT void CopyRGBToVideoFrame(const uint8* source,
diff --git a/media/base/video_util_unittest.cc b/media/base/video_util_unittest.cc
index 9ac13c1..79c5315 100644
--- a/media/base/video_util_unittest.cc
+++ b/media/base/video_util_unittest.cc
@@ -328,6 +328,8 @@ TEST_P(VideoUtilRotationTest, Rotate) {
 INSTANTIATE_TEST_CASE_P(, VideoUtilRotationTest,
                         testing::ValuesIn(kVideoRotationTestData));
 
+// Tests the ComputeLetterboxRegion function.  Also, because of shared code
+// internally, this also tests ScaleSizeToFitWithinTarget().
 TEST_F(VideoUtilTest, ComputeLetterboxRegion) {
   EXPECT_EQ(gfx::Rect(167, 0, 666, 500),
             ComputeLetterboxRegion(gfx::Rect(0, 0, 1000, 500),
@@ -348,6 +350,48 @@ TEST_F(VideoUtilTest, ComputeLetterboxRegion) {
                                      gfx::Size(0, 0)).IsEmpty());
 }
 
+TEST_F(VideoUtilTest, ScaleSizeToEncompassTarget) {
+  EXPECT_EQ(gfx::Size(1000, 750),
+            ScaleSizeToEncompassTarget(gfx::Size(640, 480),
+                                       gfx::Size(1000, 500)));
+  EXPECT_EQ(gfx::Size(1333, 1000),
+            ScaleSizeToEncompassTarget(gfx::Size(640, 480),
+                                       gfx::Size(500, 1000)));
+  EXPECT_EQ(gfx::Size(1000, 562),
+            ScaleSizeToEncompassTarget(gfx::Size(1920, 1080),
+                                       gfx::Size(1000, 500)));
+  EXPECT_EQ(gfx::Size(133, 100),
+            ScaleSizeToEncompassTarget(gfx::Size(400, 300),
+                                       gfx::Size(100, 100)));
+  EXPECT_EQ(gfx::Size(2666666666, 2000000000),
+            ScaleSizeToEncompassTarget(gfx::Size(40000, 30000),
+                                       gfx::Size(2000000000, 2000000000)));
+  EXPECT_TRUE(ScaleSizeToEncompassTarget(
+      gfx::Size(0, 0), gfx::Size(2000000000, 2000000000)).IsEmpty());
+}
+
+TEST_F(VideoUtilTest, PadToMatchAspectRatio) {
+  EXPECT_EQ(gfx::Size(640, 480),
+            PadToMatchAspectRatio(gfx::Size(640, 480), gfx::Size(640, 480)));
+  EXPECT_EQ(gfx::Size(640, 480),
+            PadToMatchAspectRatio(gfx::Size(640, 480), gfx::Size(4, 3)));
+  EXPECT_EQ(gfx::Size(960, 480),
+            PadToMatchAspectRatio(gfx::Size(640, 480), gfx::Size(1000, 500)));
+  EXPECT_EQ(gfx::Size(640, 1280),
+            PadToMatchAspectRatio(gfx::Size(640, 480), gfx::Size(500, 1000)));
+  EXPECT_EQ(gfx::Size(2160, 1080),
+            PadToMatchAspectRatio(gfx::Size(1920, 1080), gfx::Size(1000, 500)));
+  EXPECT_EQ(gfx::Size(400, 400),
+            PadToMatchAspectRatio(gfx::Size(400, 300), gfx::Size(100, 100)));
+  EXPECT_EQ(gfx::Size(400, 400),
+            PadToMatchAspectRatio(gfx::Size(300, 400), gfx::Size(100, 100)));
+  EXPECT_EQ(gfx::Size(40000, 40000),
+            PadToMatchAspectRatio(gfx::Size(40000, 30000),
+                                  gfx::Size(2000000000, 2000000000)));
+  EXPECT_TRUE(PadToMatchAspectRatio(
+      gfx::Size(40000, 30000), gfx::Size(0, 0)).IsEmpty());
+}
+
 TEST_F(VideoUtilTest, LetterboxYUV) {
   int width = 40;
   int height = 30;