Disallow setting the rate to values that would cause busy loops (< 1/16x) or rendering issues (> 16x)

BUG=18362
TEST=none
Review URL: http://codereview.chromium.org/164032

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@23037 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 32 insertions, 0 deletions

diff --git a/webkit/glue/webmediaplayer_impl.cc b/webkit/glue/webmediaplayer_impl.cc
index 0d96865..04f5dc8 100644
--- a/webkit/glue/webmediaplayer_impl.cc
+++ b/webkit/glue/webmediaplayer_impl.cc
@@ -27,6 +27,25 @@ namespace {
 // queue but gives up a pretty good latency on repaint.
 const int kMaxOutstandingRepaints = 50;
 
+// Limits the range of playback rate.
+//
+// TODO(kylep): Revisit these.
+//
+// Vista has substantially lower performance than XP or Windows7.  If you speed
+// up a video too much, it can't keep up, and rendering stops updating except on
+// the time bar. For really high speeds, audio becomes a bottleneck and we just
+// use up the data we have, which may not achieve the speed requested, but will
+// not crash the tab.
+//
+// A very slow speed, ie 0.00000001x, causes the machine to lock up. (It seems
+// like a busy loop). It gets unresponsive, although its not completely dead.
+//
+// Also our timers are not very accurate (especially for ogg), which becomes
+// evident at low speeds and on Vista. Since other speeds are risky and outside
+// the norms, we think 1/16x to 16x is a safe and useful range for now.
+const float kMinRate = 0.0625f;
+const float kMaxRate = 16.0f;
+
 }  // namespace
 
 namespace webkit_glue {
@@ -248,6 +267,19 @@ void WebMediaPlayerImpl::setEndTime(float seconds) {
 void WebMediaPlayerImpl::setRate(float rate) {
   DCHECK(MessageLoop::current() == main_loop_);
 
+  // TODO(kylep): Remove when support for negatives is added. Also, modify the
+  // following checks so rewind uses reasonable values also.
+  if (rate < 0.0f)
+    return;
+
+  // Limit rates to reasonable values by clamping.
+  if (rate != 0.0f) {
+    if (rate < kMinRate)
+      rate = kMinRate;
+    else if (rate > kMaxRate)
+      rate = kMaxRate;
+  }
+
   playback_rate_ = rate;
   if (!paused_) {
     pipeline_->SetPlaybackRate(rate);