[MSE] Fix GC with media_time past the last appended buffer timestamp

media/filters/source_buffer_stream.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // SourceBufferStream is a data structure that stores media Buffers in ranges.
 // Buffers can be appended out of presentation order. Buffers are retrieved by
 // seeking to the desired start point and calling GetNextBuffer(). Buffers are
 // returned in sequential presentation order.
 
 #ifndef MEDIA_FILTERS_SOURCE_BUFFER_STREAM_H_
@@ skipping 388 matching lines @@
   DecodeTimestamp media_segment_start_time_;
 
   // Points to the range containing the current media segment being appended.
   RangeList::iterator range_for_next_append_;
 
   // True when the next call to Append() begins a new media segment.
   bool new_media_segment_ = false;
 
   // The timestamp of the last buffer appended to the media segment, set to
   // kNoDecodeTimestamp() if the beginning of the segment.
-  DecodeTimestamp last_appended_buffer_timestamp_;
+  DecodeTimestamp last_appended_buffer_timestamp_ = kNoDecodeTimestamp();

[wolenetz, 2015/12/02 23:32:50]

Note that this is a DTS, not a PTS (pre-existing problem: see crbugs with
label:MSEptsdtsCleanup for this known issue). media_time is correctly PTS.
Buffered ranges and last_appendeded incorrectly are based on DTS.

Perhaps adjust the CL description to not mention PTS, so that it doesn't confuse
readers.

Note that DTS usually is < PTS, so the clamping CL follow-up is motivated not
just for Chromium pipeline allowing audio clock to go slightly past end of
buffered video, it's also motivated for clamping a slightly higher PTS into the
(incorrectly DTS-based-currently) buffered ranges for sane GC in out-of-order
decode streams like AVC.

+  base::TimeDelta last_appended_buffer_duration_ = kNoTimestamp();
   bool last_appended_buffer_is_keyframe_ = false;
 
   // The decode timestamp on the last buffer returned by the most recent
   // GetNextBuffer() call. Set to kNoDecodeTimestamp() if GetNextBuffer() hasn't
   // been called yet or a seek has happened since the last GetNextBuffer() call.
   DecodeTimestamp last_output_buffer_timestamp_;
 
   // Stores the largest distance between two adjacent buffers in this stream.
   base::TimeDelta max_interbuffer_distance_;
 
@@ skipping 26 matching lines @@
   int num_splice_generation_success_logs_ = 0;
   int num_track_buffer_gap_warning_logs_ = 0;
   int num_garbage_collect_algorithm_logs_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(SourceBufferStream);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_FILTERS_SOURCE_BUFFER_STREAM_H_