Bug 1500713: P3 - Prevent duration in GetBuffered from being overestimated. r=kinetik,jya

Depends on D19097

Differential Revision: https://phabricator.services.mozilla.com/D22048

--HG--
extra : moz-landing-system : lando

dom/media/mp3/MP3Demuxer.cpp

@@ -322,6 +322,13 @@ TimeIntervals MP3TrackDemuxer::GetBuffered() {
     buffered += TimeInterval(start, end);
   }
 
+  // If the number of frames reported by the header is valid,
+  // the duration calculated from it is the maximal duration.
+  if (ValidNumAudioFrames() && Duration() > TimeUnit()) {
+    TimeInterval duration = TimeInterval(TimeUnit(), Duration());
+    return buffered.Intersection(duration);
+  }
+
   return buffered;
 }
 
@@ -333,8 +340,8 @@ TimeUnit MP3TrackDemuxer::Duration() const {
   }
 
   int64_t numFrames = 0;
-  const auto numAudioFrames = mParser.VBRInfo().NumAudioFrames();
-  if (mParser.VBRInfo().IsValid() && numAudioFrames.valueOr(0) + 1 > 1) {
+  const auto numAudioFrames = ValidNumAudioFrames();
+  if (numAudioFrames) {
     // VBR headers don't include the VBR header frame.
     numFrames = numAudioFrames.value() + 1;
     return Duration(numFrames);
@@ -728,6 +735,13 @@ double MP3TrackDemuxer::AverageFrameLength() const {
   return 0.0;
 }
 
+Maybe<uint32_t> MP3TrackDemuxer::ValidNumAudioFrames() const {
+  return mParser.VBRInfo().IsValid() &&
+                 mParser.VBRInfo().NumAudioFrames().valueOr(0) + 1 > 1
+             ? mParser.VBRInfo().NumAudioFrames()
+             : Nothing();
+}
+
 }  // namespace mozilla
 
 #undef MP3LOG

dom/media/mp3/MP3Demuxer.h

@@ -122,6 +122,10 @@ class MP3TrackDemuxer : public MediaTrackDemuxer,
   // Returns the average frame length derived from the previously parsed frames.
   double AverageFrameLength() const;
 
+  // Returns the number of frames reported by the header if it's valid. Nothing
+  // otherwise.
+  Maybe<uint32_t> ValidNumAudioFrames() const;
+
   // The (hopefully) MPEG resource.
   MediaResourceIndex mSource;