Introduce audio/video BufferingState to Pipeline.

This is a stepping stone towards having audio/video renderers accurately
report their buffering state. For now we use the Preroll() callback to
signal that enough data has been buffered.

Notable changes:
  - The kStarting/kStarted states have been merged into kPlaying
  - DoPlay() is now done implicitly after entering the kPlaying state
  - Transitioning from waiting to non-waiting states (or vice versa)
    now controls the starting and stopping of playback

BUG=144683

Review URL: https://codereview.chromium.org/276973004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@269828 0039d316-1c4b-4281-b951-d872f2087c98

5 files changed, 179 insertions, 90 deletions

diff --git a/media/base/buffering_state.h b/media/base/buffering_state.h
new file mode 100644
index 0000000..3140505
--- /dev/null
+++ b/media/base/buffering_state.h
@@ -0,0 +1,26 @@
+// Copyright 2014 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 MEDIA_BASE_BUFFERING_STATE_H_
+#define MEDIA_BASE_BUFFERING_STATE_H_
+
+#include "base/callback_forward.h"
+
+namespace media {
+
+enum BufferingState {
+  // Indicates that there is no data buffered.
+  //
+  // Typical reason is data underflow and hence playback should be paused.
+  BUFFERING_HAVE_NOTHING,
+
+  // Indicates that enough data has been buffered.
+  //
+  // Typical reason is enough data has been prerolled to start playback.
+  BUFFERING_HAVE_ENOUGH,
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_BUFFERING_STATE_H_
diff --git a/media/base/pipeline.cc b/media/base/pipeline.cc
index 3cfe296..841a49b 100644
--- a/media/base/pipeline.cc
+++ b/media/base/pipeline.cc
@@ -48,6 +48,8 @@ Pipeline::Pipeline(
       audio_ended_(false),
       video_ended_(false),
       text_ended_(false),
+      audio_buffering_state_(BUFFERING_HAVE_NOTHING),
+      video_buffering_state_(BUFFERING_HAVE_NOTHING),
       demuxer_(NULL),
       creation_time_(default_tick_clock_.NowTicks()) {
   media_log_->AddEvent(media_log_->CreatePipelineStateChangedEvent(kCreated));
@@ -188,7 +190,7 @@ void Pipeline::SetErrorForTesting(PipelineStatus status) {
 }
 
 void Pipeline::SetState(State next_state) {
-  if (state_ != kStarted && next_state == kStarted &&
+  if (state_ != kPlaying && next_state == kPlaying &&
       !creation_time_.is_null()) {
     UMA_HISTOGRAM_TIMES("Media.TimeToPipelineStarted",
                         default_tick_clock_.NowTicks() - creation_time_);
@@ -211,8 +213,7 @@ const char* Pipeline::GetStateString(State state) {
     RETURN_STRING(kInitVideoRenderer);
     RETURN_STRING(kInitPrerolling);
     RETURN_STRING(kSeeking);
-    RETURN_STRING(kStarting);
-    RETURN_STRING(kStarted);
+    RETURN_STRING(kPlaying);
     RETURN_STRING(kStopping);
     RETURN_STRING(kStopped);
   }
@@ -249,15 +250,12 @@ Pipeline::State Pipeline::GetNextState() const {
       return kInitPrerolling;
 
     case kInitPrerolling:
-      return kStarting;
+      return kPlaying;
 
     case kSeeking:
-      return kStarting;
+      return kPlaying;
 
-    case kStarting:
-      return kStarted;
-
-    case kStarted:
+    case kPlaying:
     case kStopping:
     case kStopped:
       break;
@@ -364,11 +362,9 @@ void Pipeline::StateTransitionTask(PipelineStatus status) {
 
   // Guard against accidentally clearing |pending_callbacks_| for states that
   // use it as well as states that should not be using it.
-  //
-  // TODO(scherkus): Make every state transition use |pending_callbacks_|.
   DCHECK_EQ(pending_callbacks_.get() != NULL,
-            (state_ == kInitPrerolling || state_ == kStarting ||
-             state_ == kSeeking));
+            (state_ == kInitPrerolling || state_ == kSeeking));
+
   pending_callbacks_.reset();
 
   PipelineStatusCB done_cb = base::Bind(
@@ -412,29 +408,24 @@ void Pipeline::StateTransitionTask(PipelineStatus status) {
 
       return DoInitialPreroll(done_cb);
 
-    case kStarting:
-      return DoPlay(done_cb);
-
-    case kStarted:
-      {
-        base::AutoLock l(lock_);
-        // We use audio stream to update the clock. So if there is such a
-        // stream, we pause the clock until we receive a valid timestamp.
-        waiting_for_clock_update_ = true;
-        if (!audio_renderer_) {
-          clock_->SetMaxTime(clock_->Duration());
-          StartClockIfWaitingForTimeUpdate_Locked();
-        }
-      }
-
-      DCHECK(!seek_cb_.is_null());
-      DCHECK_EQ(status_, PIPELINE_OK);
-
-      // Fire canplaythrough immediately after playback begins because of
-      // crbug.com/106480.
-      // TODO(vrk): set ready state to HaveFutureData when bug above is fixed.
-      preroll_completed_cb_.Run();
-      return base::ResetAndReturn(&seek_cb_).Run(PIPELINE_OK);
+    case kPlaying:
+      PlaybackRateChangedTask(GetPlaybackRate());
+      VolumeChangedTask(GetVolume());
+
+      // We enter this state from either kInitPrerolling or kSeeking. As of now
+      // both those states call Preroll(), which means by time we enter this
+      // state we've already buffered enough data. Forcefully update the
+      // buffering state, which start the clock and renderers and transition
+      // into kPlaying state.
+      //
+      // TODO(scherkus): Remove after renderers are taught to fire buffering
+      // state callbacks http://crbug.com/144683
+      DCHECK(WaitingForEnoughData());
+      if (audio_renderer_)
+        BufferingStateChanged(&audio_buffering_state_, BUFFERING_HAVE_ENOUGH);
+      if (video_renderer_)
+        BufferingStateChanged(&video_buffering_state_, BUFFERING_HAVE_ENOUGH);
+      return;
 
     case kStopping:
     case kStopped:
@@ -469,6 +460,16 @@ void Pipeline::DoInitialPreroll(const PipelineStatusCB& done_cb) {
     bound_fns.Push(base::Bind(
         &VideoRenderer::Preroll, base::Unretained(video_renderer_.get()),
         seek_timestamp));
+
+    // TODO(scherkus): Remove after VideoRenderer is taught to fire buffering
+    // state callbacks http://crbug.com/144683
+    bound_fns.Push(base::Bind(&VideoRenderer::Play,
+                              base::Unretained(video_renderer_.get())));
+  }
+
+  if (text_renderer_) {
+    bound_fns.Push(base::Bind(
+        &TextRenderer::Play, base::Unretained(text_renderer_.get())));
   }
 
   pending_callbacks_ = SerialRunner::Run(bound_fns, done_cb);
@@ -495,10 +496,24 @@ void Pipeline::DoSeek(
   if (audio_renderer_) {
     bound_fns.Push(base::Bind(
         &AudioRenderer::Flush, base::Unretained(audio_renderer_.get())));
+
+    // TODO(scherkus): Remove after AudioRenderer is taught to fire buffering
+    // state callbacks http://crbug.com/144683
+    bound_fns.Push(base::Bind(&Pipeline::BufferingStateChanged,
+                              base::Unretained(this),
+                              &audio_buffering_state_,
+                              BUFFERING_HAVE_NOTHING));
   }
   if (video_renderer_) {
     bound_fns.Push(base::Bind(
         &VideoRenderer::Flush, base::Unretained(video_renderer_.get())));
+
+    // TODO(scherkus): Remove after VideoRenderer is taught to fire buffering
+    // state callbacks http://crbug.com/144683
+    bound_fns.Push(base::Bind(&Pipeline::BufferingStateChanged,
+                              base::Unretained(this),
+                              &video_buffering_state_,
+                              BUFFERING_HAVE_NOTHING));
   }
   if (text_renderer_) {
     bound_fns.Push(base::Bind(
@@ -520,27 +535,11 @@ void Pipeline::DoSeek(
     bound_fns.Push(base::Bind(
         &VideoRenderer::Preroll, base::Unretained(video_renderer_.get()),
         seek_timestamp));
-  }
-
-  pending_callbacks_ = SerialRunner::Run(bound_fns, done_cb);
-}
-
-void Pipeline::DoPlay(const PipelineStatusCB& done_cb) {
-  DCHECK(task_runner_->BelongsToCurrentThread());
-  DCHECK(!pending_callbacks_.get());
-  SerialRunner::Queue bound_fns;
-
-  PlaybackRateChangedTask(GetPlaybackRate());
-  VolumeChangedTask(GetVolume());
-
-  if (audio_renderer_) {
-    bound_fns.Push(base::Bind(
-        &AudioRenderer::Play, base::Unretained(audio_renderer_.get())));
-  }
 
-  if (video_renderer_) {
-    bound_fns.Push(base::Bind(
-        &VideoRenderer::Play, base::Unretained(video_renderer_.get())));
+    // TODO(scherkus): Remove after renderers are taught to fire buffering
+    // state callbacks http://crbug.com/144683
+    bound_fns.Push(base::Bind(&VideoRenderer::Play,
+                              base::Unretained(video_renderer_.get())));
   }
 
   if (text_renderer_) {
@@ -706,7 +705,7 @@ void Pipeline::PlaybackRateChangedTask(float playback_rate) {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   // Playback rate changes are only carried out while playing.
-  if (state_ != kStarting && state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   {
@@ -724,7 +723,7 @@ void Pipeline::VolumeChangedTask(float volume) {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
   // Volume changes are only carried out while playing.
-  if (state_ != kStarting && state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   if (audio_renderer_)
@@ -736,7 +735,7 @@ void Pipeline::SeekTask(TimeDelta time, const PipelineStatusCB& seek_cb) {
   DCHECK(stop_cb_.is_null());
 
   // Suppress seeking if we're not fully started.
-  if (state_ != kStarted) {
+  if (state_ != kPlaying) {
     DCHECK(state_ == kStopping || state_ == kStopped)
         << "Receive extra seek in unexpected state: " << state_;
 
@@ -770,7 +769,7 @@ void Pipeline::SeekTask(TimeDelta time, const PipelineStatusCB& seek_cb) {
 void Pipeline::DoAudioRendererEnded() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
-  if (state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   DCHECK(!audio_ended_);
@@ -789,7 +788,7 @@ void Pipeline::DoAudioRendererEnded() {
 void Pipeline::DoVideoRendererEnded() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
-  if (state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   DCHECK(!video_ended_);
@@ -801,7 +800,7 @@ void Pipeline::DoVideoRendererEnded() {
 void Pipeline::DoTextRendererEnded() {
   DCHECK(task_runner_->BelongsToCurrentThread());
 
-  if (state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   DCHECK(!text_ended_);
@@ -888,13 +887,79 @@ void Pipeline::OnAudioUnderflow() {
     return;
   }
 
-  if (state_ != kStarted)
+  if (state_ != kPlaying)
     return;
 
   if (audio_renderer_)
     audio_renderer_->ResumeAfterUnderflow();
 }
 
+void Pipeline::BufferingStateChanged(BufferingState* buffering_state,
+                                     BufferingState new_buffering_state) {
+  DVLOG(1) << __FUNCTION__ << "(" << *buffering_state << ", "
+           << " " << new_buffering_state << ") "
+           << (buffering_state == &audio_buffering_state_ ? "audio" : "video");
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  bool was_waiting_for_enough_data = WaitingForEnoughData();
+  *buffering_state = new_buffering_state;
+
+  // Renderer underflowed.
+  if (!was_waiting_for_enough_data && WaitingForEnoughData()) {
+    StartWaitingForEnoughData();
+    return;
+  }
+
+  // Renderer prerolled.
+  if (was_waiting_for_enough_data && !WaitingForEnoughData()) {
+    StartPlayback();
+    return;
+  }
+}
+
+bool Pipeline::WaitingForEnoughData() const {
+  DCHECK(task_runner_->BelongsToCurrentThread());
+  if (state_ != kPlaying)
+    return false;
+  if (audio_renderer_ && audio_buffering_state_ != BUFFERING_HAVE_ENOUGH)
+    return true;
+  if (video_renderer_ && video_buffering_state_ != BUFFERING_HAVE_ENOUGH)
+    return true;
+  return false;
+}
+
+void Pipeline::StartWaitingForEnoughData() {
+  DCHECK_EQ(state_, kPlaying);
+  DCHECK(WaitingForEnoughData());
+
+  if (audio_renderer_)
+    audio_renderer_->Pause();
+
+  base::AutoLock auto_lock(lock_);
+  clock_->Pause();
+}
+
+void Pipeline::StartPlayback() {
+  DCHECK_EQ(state_, kPlaying);
+  DCHECK(!WaitingForEnoughData());
+
+  if (audio_renderer_) {
+    audio_renderer_->Play();
+
+    base::AutoLock auto_lock(lock_);
+    // We use audio stream to update the clock. So if there is such a
+    // stream, we pause the clock until we receive a valid timestamp.
+    waiting_for_clock_update_ = true;
+  } else {
+    base::AutoLock auto_lock(lock_);
+    clock_->SetMaxTime(clock_->Duration());
+    clock_->Play();
+  }
+
+  preroll_completed_cb_.Run();
+  if (!seek_cb_.is_null())
+    base::ResetAndReturn(&seek_cb_).Run(PIPELINE_OK);
+}
+
 void Pipeline::StartClockIfWaitingForTimeUpdate_Locked() {
   lock_.AssertAcquired();
   if (!waiting_for_clock_update_)
diff --git a/media/base/pipeline.h b/media/base/pipeline.h
index c4de1ce..1464cc2 100644
--- a/media/base/pipeline.h
+++ b/media/base/pipeline.h
@@ -13,6 +13,7 @@
 #include "base/threading/thread_checker.h"
 #include "base/time/default_tick_clock.h"
 #include "media/base/audio_renderer.h"
+#include "media/base/buffering_state.h"
 #include "media/base/demuxer.h"
 #include "media/base/media_export.h"
 #include "media/base/pipeline_status.h"
@@ -58,14 +59,13 @@ typedef base::Callback<void(PipelineMetadata)> PipelineMetadataCB;
 //   [ InitXXX (for each filter) ]      [ Stopping ]
 //         |                                 |
 //         V                                 V
-//   [ InitPreroll ]                    [ Stopped ]
+//   [ InitPrerolling ]                 [ Stopped ]
 //         |
 //         V
-//   [ Starting ] <-- [ Seeking ]
+//   [ Playing ] <-- [ Seeking ]
 //         |               ^
-//         V               |
-//   [ Started ] ----------'
-//                 Seek()
+//         `---------------'
+//              Seek()
 //
 // Initialization is a series of state transitions from "Created" through each
 // filter initialization state.  When all filter initialization states have
@@ -194,8 +194,7 @@ class MEDIA_EXPORT Pipeline : public DemuxerHost {
     kInitVideoRenderer,
     kInitPrerolling,
     kSeeking,
-    kStarting,
-    kStarted,
+    kPlaying,
     kStopping,
     kStopped,
   };
@@ -305,10 +304,6 @@ class MEDIA_EXPORT Pipeline : public DemuxerHost {
   // indepentent from seeking.
   void DoSeek(base::TimeDelta seek_timestamp, const PipelineStatusCB& done_cb);
 
-  // Updates playback rate and volume and initiates an asynchronous play call
-  // sequence executing |done_cb| with the final status when completed.
-  void DoPlay(const PipelineStatusCB& done_cb);
-
   // Initiates an asynchronous pause-flush-stop call sequence executing
   // |done_cb| when completed.
   void DoStop(const PipelineStatusCB& done_cb);
@@ -316,6 +311,21 @@ class MEDIA_EXPORT Pipeline : public DemuxerHost {
 
   void OnAudioUnderflow();
 
+  // Collection of callback methods and helpers for tracking changes in
+  // buffering state and transition from paused/underflow states and playing
+  // states.
+  //
+  // While in the kPlaying state:
+  //   - A waiting to non-waiting transition indicates preroll has completed
+  //     and StartPlayback() should be called
+  //   - A non-waiting to waiting transition indicates underflow has occurred
+  //     and StartWaitingForEnoughData() should be called
+  void BufferingStateChanged(BufferingState* buffering_state,
+                             BufferingState new_buffering_state);
+  bool WaitingForEnoughData() const;
+  void StartWaitingForEnoughData();
+  void StartPlayback();
+
   void StartClockIfWaitingForTimeUpdate_Locked();
 
   // Task runner used to execute pipeline tasks.
@@ -377,6 +387,9 @@ class MEDIA_EXPORT Pipeline : public DemuxerHost {
   bool video_ended_;
   bool text_ended_;
 
+  BufferingState audio_buffering_state_;
+  BufferingState video_buffering_state_;
+
   // Temporary callback used for Start() and Seek().
   PipelineStatusCB seek_cb_;
 
diff --git a/media/base/pipeline_unittest.cc b/media/base/pipeline_unittest.cc
index d2a7a8f..81575e3 100644
--- a/media/base/pipeline_unittest.cc
+++ b/media/base/pipeline_unittest.cc
@@ -860,7 +860,6 @@ class PipelineTeardownTest : public PipelineTest {
     kFlushing,
     kSeeking,
     kPrerolling,
-    kStarting,
     kPlaying,
   };
 
@@ -885,7 +884,6 @@ class PipelineTeardownTest : public PipelineTest {
       case kFlushing:
       case kSeeking:
       case kPrerolling:
-      case kStarting:
         DoInitialize(state, stop_or_error);
         DoSeek(state, stop_or_error);
         break;
@@ -1107,18 +1105,6 @@ class PipelineTeardownTest : public PipelineTest {
     EXPECT_CALL(*video_renderer_, SetPlaybackRate(0.0f));
     EXPECT_CALL(*audio_renderer_, SetVolume(1.0f));
 
-    if (state == kStarting) {
-      if (stop_or_error == kStop) {
-        EXPECT_CALL(*audio_renderer_, Play())
-            .WillOnce(Stop(pipeline_.get(), stop_cb));
-      } else {
-        status = PIPELINE_ERROR_READ;
-        EXPECT_CALL(*audio_renderer_, Play())
-            .WillOnce(SetError(pipeline_.get(), status));
-      }
-      return status;
-    }
-
     NOTREACHED() << "State not supported: " << state;
     return status;
   }
@@ -1168,7 +1154,6 @@ INSTANTIATE_TEARDOWN_TEST(Stop, Pausing);
 INSTANTIATE_TEARDOWN_TEST(Stop, Flushing);
 INSTANTIATE_TEARDOWN_TEST(Stop, Seeking);
 INSTANTIATE_TEARDOWN_TEST(Stop, Prerolling);
-INSTANTIATE_TEARDOWN_TEST(Stop, Starting);
 INSTANTIATE_TEARDOWN_TEST(Stop, Playing);
 
 INSTANTIATE_TEARDOWN_TEST(Error, InitDemuxer);
@@ -1178,7 +1163,6 @@ INSTANTIATE_TEARDOWN_TEST(Error, Pausing);
 INSTANTIATE_TEARDOWN_TEST(Error, Flushing);
 INSTANTIATE_TEARDOWN_TEST(Error, Seeking);
 INSTANTIATE_TEARDOWN_TEST(Error, Prerolling);
-INSTANTIATE_TEARDOWN_TEST(Error, Starting);
 INSTANTIATE_TEARDOWN_TEST(Error, Playing);
 
 INSTANTIATE_TEARDOWN_TEST(ErrorAndStop, Playing);
diff --git a/media/media.gyp b/media/media.gyp
index 5a974aa..c42d270 100644
--- a/media/media.gyp
+++ b/media/media.gyp
@@ -248,6 +248,7 @@
         'base/bit_reader_core.cc',
         'base/bit_reader_core.h',
         'base/bitstream_buffer.h',
+        'base/buffering_state.h',
         'base/buffers.h',
         'base/byte_queue.cc',
         'base/byte_queue.h',