Bug 1207946: [MSE] P3. Reset cached demuxing index when new data overwrite the end. r=gerald

This will force an iterative search upon the next demux request.

dom/media/mediasource/TrackBuffersManager.cpp

@@ -1660,11 +1660,14 @@ TrackBuffersManager::InsertFrames(TrackBuffer& aSamples,
   }
 
   // Adjust our demuxing index if necessary.
-  if (trackBuffer.mNextGetSampleIndex.isSome() &&
-      (trackBuffer.mNextInsertionIndex.ref() < trackBuffer.mNextGetSampleIndex.ref() ||
-       (trackBuffer.mNextInsertionIndex.ref() == trackBuffer.mNextGetSampleIndex.ref() &&
-        aIntervals.GetEnd() < trackBuffer.mNextSampleTime))) {
-    trackBuffer.mNextGetSampleIndex.ref() += aSamples.Length();
+  if (trackBuffer.mNextGetSampleIndex.isSome()) {
+    if (trackBuffer.mNextInsertionIndex.ref() == trackBuffer.mNextGetSampleIndex.ref() &&
+        aIntervals.GetEnd() >= trackBuffer.mNextSampleTime) {
+      MSE_DEBUG("Next sample to be played got overwritten");
+      trackBuffer.mNextGetSampleIndex.reset();
+    } else if (trackBuffer.mNextInsertionIndex.ref() <= trackBuffer.mNextGetSampleIndex.ref()) {
+      trackBuffer.mNextGetSampleIndex.ref() += aSamples.Length();
+    }
   }
 
   TrackBuffer& data = trackBuffer.mBuffers.LastElement();

dom/media/mediasource/TrackBuffersManager.h

@@ -263,6 +263,8 @@ private:
     nsRefPtr<SharedTrackInfo> mLastInfo;
 
     // If set, position of the next sample to be retrieved by GetSample().
+    // If the position is equal to the TrackBuffer's length, it indicates that
+    // we've reached EOS.
     Maybe<uint32_t> mNextGetSampleIndex;
     // Approximation of the next sample's decode timestamp.
     media::TimeUnit mNextSampleTimecode;