Bug 1194624: [MSE] P3. Determine when canplaythrough can be fired. r=jwwang

We assume that if we have 30s of data buffered ahead of the current position or up to the element's duration that we can play ahead without interruption.

dom/media/MediaDecoder.h

@@ -577,7 +577,7 @@ private:
 
   // Returns true if we can play the entire media through without stopping
   // to buffer, given the current download and playback rates.
-  bool CanPlayThrough();
+  virtual bool CanPlayThrough();
 
   void SetAudioChannel(dom::AudioChannel aChannel) { mAudioChannel = aChannel; }
   dom::AudioChannel GetAudioChannel() { return mAudioChannel; }

dom/media/mediasource/MediaSourceDecoder.cpp

@@ -16,6 +16,7 @@
 #include "MediaFormatReader.h"
 #include "MediaSourceDemuxer.h"
 #include "SourceBufferList.h"
+#include <algorithm>
 
 extern mozilla::LogModule* GetMediaSourceLog();
 
@@ -265,6 +266,32 @@ MediaSourceDecoder::NextFrameBufferedStatus()
     : MediaDecoderOwner::NEXT_FRAME_UNAVAILABLE;
 }
 
+bool
+MediaSourceDecoder::CanPlayThrough()
+{
+  MOZ_ASSERT(NS_IsMainThread());
+  if (IsNaN(mMediaSource->Duration())) {
+    // Don't have any data yet.
+    return false;
+  }
+  TimeUnit duration = TimeUnit::FromSeconds(mMediaSource->Duration());
+  TimeUnit currentPosition = TimeUnit::FromMicroseconds(CurrentPosition());
+  if (duration.IsInfinite()) {
+    // We can't make an informed decision and just assume that it's a live stream
+    return true;
+  } else if (duration <= currentPosition) {
+    return true;
+  }
+  // If we have data up to the mediasource's duration or 30s ahead, we can
+  // assume that we can play without interruption.
+  TimeUnit timeAhead =
+    std::min(duration, currentPosition + TimeUnit::FromSeconds(30));
+  TimeInterval interval(currentPosition,
+                        timeAhead,
+                        MediaSourceDemuxer::EOS_FUZZ);
+  return GetBuffered().Contains(interval);
+}
+
 #undef MSE_DEBUG
 #undef MSE_DEBUGV
 

dom/media/mediasource/MediaSourceDecoder.h

@@ -78,6 +78,7 @@ public:
   void AddSizeOfResources(ResourceSizes* aSizes) override;
 
   MediaDecoderOwner::NextFrameStatus NextFrameBufferedStatus() override;
+  bool CanPlayThrough() override;
 
 private:
   void DoSetMediaSourceDuration(double aDuration);