From b55038bbf2f7512cae0a5688a0eba561a33137e3 Mon Sep 17 00:00:00 2001
From: Nicolas Silva <nsilva@mozilla.com>
Date: Fri, 28 Sep 2012 13:34:03 -0400
Subject: [PATCH] Bug 794747 - add a pref for the default size of the
 VideoQueue. r=kinetik

---
 .../media/nsBuiltinDecoderStateMachine.cpp    | 33 ++++++++++---------
 content/media/nsBuiltinDecoderStateMachine.h  |  4 +++
 modules/libpref/src/init/all.js               |  4 +++
 3 files changed, 26 insertions(+), 15 deletions(-)

diff --git a/content/media/nsBuiltinDecoderStateMachine.cpp b/content/media/nsBuiltinDecoderStateMachine.cpp
index 100423bf1c7..6cae9596032 100644
--- a/content/media/nsBuiltinDecoderStateMachine.cpp
+++ b/content/media/nsBuiltinDecoderStateMachine.cpp
@@ -60,19 +60,6 @@ const uint32_t SILENCE_BYTES_CHUNK = 32 * 1024;
 // which is at or after the current playback position.
 static const uint32_t LOW_VIDEO_FRAMES = 1;
 
-// If we've got more than AMPLE_VIDEO_FRAMES decoded video frames waiting in
-// the video queue, we will not decode any more video frames until some have
-// been consumed by the play state machine thread.
-#ifdef MOZ_WIDGET_GONK
-// On B2G this is decided by a similar value which varies for each OMX decoder
-// |OMX_PARAM_PORTDEFINITIONTYPE::nBufferCountMin|. This number must be less
-// than the OMX equivalent or gecko will think it is chronically starved of
-// video frames. All decoders seen so far have a value of at least 4.
-static const uint32_t AMPLE_VIDEO_FRAMES = 3;
-#else
-static const uint32_t AMPLE_VIDEO_FRAMES = 10;
-#endif
-
 // Arbitrary "frame duration" when playing only audio.
 static const int AUDIO_DURATION_USECS = 40000;
 
@@ -430,6 +417,22 @@ nsBuiltinDecoderStateMachine::nsBuiltinDecoderStateMachine(nsBuiltinDecoder* aDe
 
   mBufferingWait = mRealTime ? 0 : BUFFERING_WAIT_S;
   mLowDataThresholdUsecs = mRealTime ? 0 : LOW_DATA_THRESHOLD_USECS;
+
+  // If we've got more than mAmpleVideoFrames decoded video frames waiting in
+  // the video queue, we will not decode any more video frames until some have
+  // been consumed by the play state machine thread.
+#ifdef MOZ_WIDGET_GONK
+  // On B2G this is decided by a similar value which varies for each OMX decoder
+  // |OMX_PARAM_PORTDEFINITIONTYPE::nBufferCountMin|. This number must be less
+  // than the OMX equivalent or gecko will think it is chronically starved of
+  // video frames. All decoders seen so far have a value of at least 4.
+  mAmpleVideoFrames = Preferences::GetUint("media.video-queue.default-size", 3);
+#else
+  mAmpleVideoFrames = Preferences::GetUint("media.video-queue.default-size", 10);
+#endif
+  if (mAmpleVideoFrames < 2) {
+    mAmpleVideoFrames = 2;
+  }
 }
 
 nsBuiltinDecoderStateMachine::~nsBuiltinDecoderStateMachine()
@@ -750,7 +753,7 @@ bool nsBuiltinDecoderStateMachine::HaveEnoughDecodedVideo()
 {
   mDecoder->GetReentrantMonitor().AssertCurrentThreadIn();
 
-  if (static_cast<uint32_t>(mReader->VideoQueue().GetSize()) < AMPLE_VIDEO_FRAMES) {
+  if (static_cast<uint32_t>(mReader->VideoQueue().GetSize()) < mAmpleVideoFrames) {
     return false;
   }
 
@@ -786,7 +789,7 @@ void nsBuiltinDecoderStateMachine::DecodeLoop()
 
   // Once we've decoded more than videoPumpThreshold video frames, we'll
   // no longer be considered to be "pumping video".
-  const unsigned videoPumpThreshold = mRealTime ? 0 : AMPLE_VIDEO_FRAMES / 2;
+  const unsigned videoPumpThreshold = mRealTime ? 0 : mAmpleVideoFrames / 2;
 
   // After the audio decode fills with more than audioPumpThreshold usecs
   // of decoded audio, we'll start to check whether the audio or video decode
diff --git a/content/media/nsBuiltinDecoderStateMachine.h b/content/media/nsBuiltinDecoderStateMachine.h
index 59007404f02..255b59b7a04 100644
--- a/content/media/nsBuiltinDecoderStateMachine.h
+++ b/content/media/nsBuiltinDecoderStateMachine.h
@@ -605,6 +605,10 @@ protected:
   uint32_t mBufferingWait;
   int64_t  mLowDataThresholdUsecs;
 
+  // If we've got more than mAmpleVideoFrames decoded video frames waiting in
+  // the video queue, we will not decode any more video frames until some have
+  // been consumed by the play state machine thread.
+  uint32_t mAmpleVideoFrames;
   // True if we shouldn't play our audio (but still write it to any capturing
   // streams).
   bool mAudioCaptured;
diff --git a/modules/libpref/src/init/all.js b/modules/libpref/src/init/all.js
index 112ba928b3a..7edf9180188 100644
--- a/modules/libpref/src/init/all.js
+++ b/modules/libpref/src/init/all.js
@@ -182,6 +182,10 @@ pref("media.webaudio.enabled", false);
 // Whether to autostart a media element with an |autoplay| attribute
 pref("media.autoplay.enabled", true);
 
+// The default number of decoded video frames that are enqueued in
+// nsBuiltinDecoderReader's mVideoQueue.
+pref("media.video-queue.default-size", 10);
+
 // 0 = Off, 1 = Full, 2 = Tagged Images Only. 
 // See eCMSMode in gfx/thebes/gfxPlatform.h
 pref("gfx.color_management.mode", 2);