Implement opus seek preroll for MediaSourceExtensions.

media/filters/source_buffer_range.cc

Index: media/filters/source_buffer_range.cc
diff --git a/media/filters/source_buffer_range.cc b/media/filters/source_buffer_range.cc
index dcade63f9221f1ad530057efc4b6c6c9cf6ab9e9..f07cae6c5e0fe19f7b28f7e3bc7e8d9990f4724d 100644
--- a/media/filters/source_buffer_range.cc
+++ b/media/filters/source_buffer_range.cc
@@ -106,6 +106,45 @@ void SourceBufferRange::Seek(DecodeTimestamp timestamp) {
       << next_buffer_index_ << ", size = " << buffers_.size();
 }
 
+int SourceBufferRange::GetConfigIdAtTime(DecodeTimestamp timestamp) {
+  DCHECK(CanSeekTo(timestamp));
+  DCHECK(!keyframe_map_.empty());
+
+  KeyframeMap::iterator result = GetFirstKeyframeAtOrBefore(timestamp);
+  size_t buffer_index = result->second - keyframe_map_index_base_;
+  CHECK_LT(buffer_index, buffers_.size()) << buffer_index
+                                          << ", size = " << buffers_.size();
+
+  return buffers_[buffer_index]->GetSpliceBufferConfigId(0);
+}
+
+bool SourceBufferRange::SameConfigThruRange(DecodeTimestamp start,
+                                            DecodeTimestamp end) {
+  DCHECK(CanSeekTo(start));
+  DCHECK(CanSeekTo(end));
+  DCHECK(start <= end);
+  DCHECK(!keyframe_map_.empty());
+
+  if (start == end)
+    return true;

[wolenetz, 2016/07/25 21:49:02]

What if the buffer at this time contains splice buffers with differing config
IDs? Also note that the splice buffers' decode comes before this time, in
reality, in part to support preroll of cross-fade IIUC. Please document intent
for these methods -- would really help review.

[chcunningham, 2016/12/01 17:07:16]

Splicing is gone. Now just checking the config ID on the buffer itself.

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

Acknowledged.

+
+  KeyframeMap::const_iterator result = GetFirstKeyframeAtOrBefore(start);
+  size_t buffer_index = result->second - keyframe_map_index_base_;
+  CHECK_LT(buffer_index, buffers_.size()) << buffer_index
+                                          << ", size = " << buffers_.size();
+
+  int start_config = buffers_[buffer_index]->GetSpliceBufferConfigId(0);
+  buffer_index++;
+  while (buffer_index < buffers_.size() &&
+         buffers_[buffer_index]->GetDecodeTimestamp() <= end) {
+    if (buffers_[buffer_index]->GetSpliceBufferConfigId(0) != start_config)

[wolenetz, 2016/07/25 21:49:02]

Ditto: if there is a splice buffer, it/they could have different config ID than
the buffer at buffers_[buffer_index]

[chcunningham, 2016/12/01 17:07:16]

Ditto.

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

Acknowledged.

+      return false;
+    buffer_index++;
+  }
+
+  return true;
+}
+
 void SourceBufferRange::SeekAheadTo(DecodeTimestamp timestamp) {
   SeekAhead(timestamp, false);
 }