Add gapless playback support for AAC playback.

media/filters/frame_processor_base.cc

Index: media/filters/frame_processor_base.cc
diff --git a/media/filters/frame_processor_base.cc b/media/filters/frame_processor_base.cc
index 09b1b86c3b39011ce2d0a6cc406ebc80af98ef15..8e888922760b5a70c598f7dda918628d31daf634 100644
--- a/media/filters/frame_processor_base.cc
+++ b/media/filters/frame_processor_base.cc
@@ -97,4 +97,65 @@ void FrameProcessorBase::NotifyNewMediaSegmentStarting(
   }
 }
 
+bool FrameProcessorBase::HandlePartialAppendWindowTrimming(
+    base::TimeDelta append_window_start,
+    base::TimeDelta append_window_end,
+    base::TimeDelta frame_start_timestamp,
+    base::TimeDelta frame_end_timestamp,
+    const scoped_refptr<StreamParserBuffer>& buffer) {
+  // Ignore any buffers which start after |append_window_start| or end after

[acolwell GONE FROM CHROMIUM, 2014/05/23 17:27:30]

DCHECK(DemuxerStream::AUDIO, buffer->type()) since all this code is assuming
audio right now.

[DaleCurtis, 2014/05/23 21:46:26]

Done.

+  // |append_window_end|.  For simplicity, even those that start before
+  // |append_window_start|.
+  if (frame_start_timestamp > append_window_start ||
+      frame_end_timestamp > append_window_end) {
+    // TODO(dalecurtis): Partial append window trimming could also be done
+    // around |append_window_end|, but is not necessary since splice frames
+    // cover overlaps there.
+    return false;
+  }
+
+  // If the buffer is entirely before |append_window_start|, save it as preroll
+  // for the first buffer which overlaps |append_window_start|.
+  if (frame_start_timestamp < append_window_start &&
+      frame_end_timestamp <= append_window_start) {
+    audio_preroll_buffer_ = buffer;
+    audio_preroll_buffer_->set_timestamp(frame_start_timestamp);

[wolenetz, 2014/05/23 19:59:45]

also SetDecodeTimestamp()?

[DaleCurtis, 2014/05/23 21:46:26]

I don't think it's necessary.

+    audio_preroll_buffer_->set_duration(frame_end_timestamp -
+                                        frame_start_timestamp);
+    return false;
+  }
+
+  // See if a partial discard can be done around |append_window_start|.
+  DCHECK(frame_start_timestamp <= append_window_start);
+  DCHECK(buffer->IsKeyframe());
+  DVLOG(1) << "Truncating buffer which overlaps append window start."
+           << " presentation_timestamp " << frame_start_timestamp.InSecondsF()
+           << " append_window_start " << append_window_start.InSecondsF();
+
+  // If this isn't the first buffer discarded by the append window, try to use
+  // the last buffer discarded for preroll.  This ensures that the partially
+  // trimmed buffer can be correctly decoded.
+  if (audio_preroll_buffer_) {
+    if (audio_preroll_buffer_->timestamp() +
+            audio_preroll_buffer_->duration() ==
+        frame_start_timestamp) {
+      buffer->SetPrerollBuffer(audio_preroll_buffer_);
+    }

[wolenetz, 2014/05/23 19:59:45]

nit: MEDIA_LOG when an audio_preroll_buffer exists but does *not* abut the next
buffer?

[DaleCurtis, 2014/05/23 21:46:26]

For another CL, MEDIA_LOG isn't available here.

+    audio_preroll_buffer_ = NULL;
+  }
+
+  // Adjust the timestamp of this buffer forward to |append_window_start|.
+  buffer->set_timestamp(append_window_start);

[acolwell GONE FROM CHROMIUM, 2014/05/23 17:27:30]

Shouldn't these 2 calls also only need to happen if the condition below is true?
If this is just to cause the preroll buffer timestamps to get changed, should
that occur in the block above instead so it is more explicit?

[DaleCurtis, 2014/05/23 21:46:26]

Correct. Seems unnecessary to duplicate these sets, but if you feel strongly I
can do so.  I've added a clarifying comment at least.

+  buffer->SetDecodeTimestamp(append_window_start);
+
+  // Decrease the duration appropriately.  We only need to shorten the buffer if
+  // it overlaps |append_window_start|.
+  if (frame_start_timestamp < append_window_start) {
+    buffer->set_discard_padding(std::make_pair(
+        append_window_start - frame_start_timestamp, base::TimeDelta()));
+    buffer->set_duration(frame_end_timestamp - append_window_start);
+  }
+  return true;
+}
+
 }  // namespace media