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

media/filters/opus_audio_decoder.cc

 // 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.
 
 #include "media/filters/opus_audio_decoder.h"
 
 #include <cmath>
 
 #include "base/single_thread_task_runner.h"
 #include "base/sys_byteorder.h"
@@ skipping 400 matching lines @@
   }
 
   status = opus_multistream_decoder_ctl(
       opus_decoder_, OPUS_SET_GAIN(opus_extra_data.gain_db));
   if (status != OPUS_OK) {
     DLOG(ERROR) << "Failed to set OPUS header gain; status="
                 << opus_strerror(status);
     return false;
   }
 
-  discard_helper_.reset(new AudioDiscardHelper(config_.samples_per_second()));
+  discard_helper_.reset(
+      new AudioDiscardHelper(config_.samples_per_second(), 0));
   start_input_timestamp_ = kNoTimestamp();
   return true;
 }
 
 void OpusAudioDecoder::CloseDecoder() {
   if (opus_decoder_) {
     opus_multistream_decoder_destroy(opus_decoder_);
     opus_decoder_ = NULL;
   }
 }
@@ skipping 43 matching lines @@
     output_buffer->get()->TrimEnd(trim_frames);
 
   // Handles discards and timestamping.  Discard the buffer if more data needed.
   if (!discard_helper_->ProcessBuffers(input, *output_buffer))
     *output_buffer = NULL;
 
   return true;
 }
 
 }  // namespace media