Implement opus seek preroll for MediaSourceExtensions.

media/filters/source_buffer_stream.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/source_buffer_stream.h"
 
 #include <algorithm>
 #include <map>
 #include <sstream>
 
@@ skipping 1087 matching lines @@
 
   RangeList::iterator itr = ranges_.end();
   for (itr = ranges_.begin(); itr != ranges_.end(); ++itr) {
     if ((*itr)->CanSeekTo(seek_dts))
       break;
   }
 
   if (itr == ranges_.end())
     return;
 
+  if (!audio_configs_.empty()) {
+    const auto& config = audio_configs_[(*itr)->GetConfigIdAtTime(seek_dts)];
+    if (config.codec() == kCodecOpus) {
+      DecodeTimestamp preroll_dts = std::max(seek_dts - config.seek_preroll(),
+                                             (*itr)->GetStartTimestamp());
+      if ((*itr)->CanSeekTo(preroll_dts) &&

[chcunningham, 2016/07/22 01:50:28]

FYI: I've taken a conservative approach here. If we cant seek back far enough to
do the proll, or if the configs don't match, we don't preroll (same as today).

[wolenetz, 2016/12/02 00:18:49]

Acknowledged.

+          (*itr)->SameConfigThruRange(preroll_dts, seek_dts)) {
+        seek_dts = preroll_dts;
+      }
+    }
+  }
+
   SeekAndSetSelectedRange(*itr, seek_dts);
   seek_pending_ = false;
 }
 
 bool SourceBufferStream::IsSeekPending() const {
   return seek_pending_ && !IsEndOfStreamReached();
 }
 
 void SourceBufferStream::OnSetDuration(base::TimeDelta duration) {
   DecodeTimestamp duration_dts =
@@ skipping 695 matching lines @@
     return false;
 
   DCHECK_NE(have_splice_buffers, have_preroll_buffer);
   splice_buffers_index_ = 0;
   pending_buffer_.swap(*out_buffer);
   pending_buffers_complete_ = false;
   return true;
 }
 
 }  // namespace media