Support start trimming post-decoding. Use it with FFmpegDemuxer.

media/formats/webm/webm_cluster_parser.cc

 // Copyright 2014 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.
 
 #include "media/formats/webm/webm_cluster_parser.h"
 
 #include <vector>
 
 #include "base/logging.h"
 #include "base/sys_byteorder.h"
@@ skipping 398 matching lines @@
 
   if (block_duration >= 0) {
     buffer->set_duration(base::TimeDelta::FromMicroseconds(
         block_duration * timecode_multiplier_));
   } else {
     DCHECK_NE(buffer_type, DemuxerStream::TEXT);
     buffer->set_duration(track->default_duration());
   }
 
   if (discard_padding != 0) {
-    buffer->set_discard_padding(base::TimeDelta::FromMicroseconds(
-                                    discard_padding / 1000));
+    buffer->set_discard_padding(std::make_pair(
+        base::TimeDelta(),
+        base::TimeDelta::FromMicroseconds(discard_padding / 1000)));

[wolenetz, 2014/05/05 19:01:23]

Matroska allows for negative DiscardPadding to indicate start discard, and
positive for end discard.

Do any of our WebM-parsed formats possibly include negative DiscardPadding
(start discard)? If so, account for it here. If not, add DLOG(ERROR... or
CHECK(... ?

[DaleCurtis, 2014/05/05 20:16:03]

I didn't know that.  If WebM supports that, probably this code should be setting
start padding to -discard_padding then.  There'a a DCHECK in the
AudioDiscardHelper against negative values.

acolwell: WDYT?

   }
 
   return track->AddBuffer(buffer);
 }
 
 WebMClusterParser::Track::Track(int track_num,
                                 bool is_video,
                                 base::TimeDelta default_duration,
                                 const LogCB& log_cb)
     : track_num_(track_num),
@@ skipping 245 matching lines @@
 WebMClusterParser::FindTextTrack(int track_num) {
   const TextTrackMap::iterator it = text_track_map_.find(track_num);
 
   if (it == text_track_map_.end())
     return NULL;
 
   return &it->second;
 }
 
 }  // namespace media