Bug 1466606 - P2. Re-use code to determine NextGetSample index. r=bryce

Previous commit added SetNextGetSampleIndexIfNeeded, let's re-use it for GetSample.
We continue to have an exception code as it caters for the most common code path, which is we retrieve one sample after the other.

MozReview-Commit-ID: HOQ53qwZj7w

--HG--
extra : rebase_source : cc9bc0b41a7085d28554f7ed764a18decfea327d

dom/media/mediasource/TrackBuffersManager.cpp

@@ -2336,17 +2336,6 @@ TrackBuffersManager::GetSample(TrackInfo::TrackType aTrack,
 
   aResult = NS_ERROR_DOM_MEDIA_WAITING_FOR_DATA;
 
-  if (!track.Length()) {
-    aResult = NS_ERROR_DOM_MEDIA_END_OF_STREAM;
-    return nullptr;
-  }
-
-  if (trackData.mNextGetSampleIndex.isNothing() &&
-      trackData.mNextSampleTimecode == TimeUnit()) {
-    // First demux, get first sample.
-    trackData.mNextGetSampleIndex = Some(0u);
-  }
-
   if (trackData.mNextGetSampleIndex.isSome()) {
     if (trackData.mNextGetSampleIndex.ref() >= track.Length()) {
       aResult = NS_ERROR_DOM_MEDIA_END_OF_STREAM;
@@ -2393,24 +2382,16 @@ TrackBuffersManager::GetSample(TrackInfo::TrackType aTrack,
     return p.forget();
   }
 
-  if (trackData.mNextSampleTimecode >
-      track.LastElement()->mTimecode + track.LastElement()->mDuration) {
-    // The next element is past our last sample. We're done.
-    trackData.mNextGetSampleIndex = Some(uint32_t(track.Length()));
-    aResult = NS_ERROR_DOM_MEDIA_END_OF_STREAM;
-    return nullptr;
-  }
+  aResult = SetNextGetSampleIndexIfNeeded(aTrack, aFuzz);
 
-  // Our previous index has been overwritten, attempt to find the new one.
-  int32_t pos = FindCurrentPosition(aTrack, aFuzz);
-  if (pos < 0) {
-    MSE_DEBUG("Couldn't find sample (pts:%" PRId64 " dts:%" PRId64 ")",
-              trackData.mNextSampleTime.ToMicroseconds(),
-              trackData.mNextSampleTimecode.ToMicroseconds());
+  if (NS_FAILED(aResult)) {
     return nullptr;
   }
 
-  const RefPtr<MediaRawData>& sample = track[pos];
+  MOZ_RELEASE_ASSERT(trackData.mNextGetSampleIndex.isSome() &&
+                     trackData.mNextGetSampleIndex.ref() < track.Length());
+  const RefPtr<MediaRawData>& sample =
+    track[trackData.mNextGetSampleIndex.ref()];
   RefPtr<MediaRawData> p = sample->Clone();
   if (!p) {
     // OOM
@@ -2419,15 +2400,14 @@ TrackBuffersManager::GetSample(TrackInfo::TrackType aTrack,
   }
 
   // Find the previous keyframe to calculate the evictable amount.
-  int32_t i = pos;
+  uint32_t i = trackData.mNextGetSampleIndex.ref();
   for (; !track[i]->mKeyframe; i--) {
   }
   UpdateEvictionIndex(trackData, i);
 
-  trackData.mNextGetSampleIndex = Some(uint32_t(pos)+1);
+  trackData.mNextGetSampleIndex.ref()++;
   trackData.mNextSampleTimecode = sample->mTimecode + sample->mDuration;
   trackData.mNextSampleTime = sample->GetEndTime();
-  aResult = NS_OK;
   return p.forget();
 }
 
@@ -2564,6 +2544,9 @@ TrackBuffersManager::SetNextGetSampleIndexIfNeeded(TrackInfo::TrackType aTrack,
   int32_t pos = FindCurrentPosition(aTrack, aFuzz);
   if (pos < 0) {
     // Not found, must wait for more data.
+    MSE_DEBUG("Couldn't find sample (pts:%" PRId64 " dts:%" PRId64 ")",
+              trackData.mNextSampleTime.ToMicroseconds(),
+              trackData.mNextSampleTimecode.ToMicroseconds());
     return NS_ERROR_DOM_MEDIA_WAITING_FOR_DATA;
   }
   trackData.mNextGetSampleIndex = Some(uint32_t(pos));