Move 'mdat' advancement logic to make more sense.

media/mp4/mp4_stream_parser.cc

Index: media/mp4/mp4_stream_parser.cc
diff --git a/media/mp4/mp4_stream_parser.cc b/media/mp4/mp4_stream_parser.cc
index 9d51959a3a32bbc8d45c0c4db8370c80e1093737..2b5eea3fd91c0ec809fe3082d442911b26ecacab 100644
--- a/media/mp4/mp4_stream_parser.cc
+++ b/media/mp4/mp4_stream_parser.cc
@@ -80,11 +80,7 @@ bool MP4StreamParser::Parse(const uint8* buf, int size) {
 
   do {
     if (state_ == kParsingBoxes) {
-      if (mdat_tail_ > queue_.head()) {
-        result = queue_.Trim(mdat_tail_);
-      } else {
-        result = ParseBox(&err);
-      }
+      result = ParseBox(&err);
     } else {
       DCHECK_EQ(kEmittingSamples, state_);
       result = EnqueueSample(&audio_buffers, &video_buffers, &err);
@@ -322,6 +318,11 @@ bool MP4StreamParser::EnqueueSample(BufferQueue* audio_buffers,
     if (*err)
       return false;
 
+    // Remain in kEnqueueingSamples state, discarding data, until the end of
+    // the current 'mdat' box has been appended to the queue.
+    if (!queue_.Trim(mdat_tail_))
+      return false;
+
     ChangeState(kParsingBoxes);
     end_of_segment_cb_.Run();
     return true;