Add gapless playback support for AAC playback.

media/filters/frame_processor.cc

Index: media/filters/frame_processor.cc
diff --git a/media/filters/frame_processor.cc b/media/filters/frame_processor.cc
index 7f83a226b75cb9ad3165a81c115c72d1371e3510..e867df7c985ea76f7825b2d01eb069e394d610f2 100644
--- a/media/filters/frame_processor.cc
+++ b/media/filters/frame_processor.cc
@@ -75,11 +75,12 @@ bool FrameProcessor::ProcessFrames(
   return true;
 }
 
-bool FrameProcessor::ProcessFrame(scoped_refptr<StreamParserBuffer> frame,
-                                  base::TimeDelta append_window_start,
-                                  base::TimeDelta append_window_end,
-                                  base::TimeDelta* timestamp_offset,
-                                  bool* new_media_segment) {
+bool FrameProcessor::ProcessFrame(
+    const scoped_refptr<StreamParserBuffer>& frame,
+    base::TimeDelta append_window_start,
+    base::TimeDelta append_window_end,
+    base::TimeDelta* timestamp_offset,
+    bool* new_media_segment) {
   // Implements the loop within step 1 of the coded frame processing algorithm
   // for a single input frame per April 1, 2014 MSE spec editor's draft:
   // https://dvcs.w3.org/hg/html-media/raw-file/d471a4412040/media-source/
@@ -263,45 +264,29 @@ bool FrameProcessor::ProcessFrame(scoped_refptr<StreamParserBuffer> frame,
     // 11. If frame end timestamp is greater than appendWindowEnd, then set the
     //     need random access point flag to true, drop the coded frame, and jump
     //     to the top of the loop to start processing the next coded frame.
-    if (presentation_timestamp < append_window_start ||
-        frame_end_timestamp > append_window_end) {
-      // See if a partial discard can be done around |append_window_start|.
-      // TODO(wolenetz): Refactor this into a base helper across legacy and
-      // new frame processors?
-      if (track_buffer->stream()->supports_partial_append_window_trimming() &&
-          presentation_timestamp < append_window_start &&
-          frame_end_timestamp > append_window_start &&
-          frame_end_timestamp <= append_window_end) {
-        DCHECK(frame->IsKeyframe());
-        DVLOG(1) << "Truncating buffer which overlaps append window start."
-                 << " presentation_timestamp "
-                 << presentation_timestamp.InSecondsF()
-                 << " append_window_start " << append_window_start.InSecondsF();
-
-        // Adjust the timestamp of this frame forward to |append_window_start|,
-        // while decreasing the duration appropriately.
-        frame->set_discard_padding(std::make_pair(
-            append_window_start - presentation_timestamp, base::TimeDelta()));
-        presentation_timestamp = append_window_start;  // |frame| updated below.
-        decode_timestamp = append_window_start;  // |frame| updated below.
-        frame_duration = frame_end_timestamp - presentation_timestamp;
-        frame->set_duration(frame_duration);
-
-        // TODO(dalecurtis): This could also be done with |append_window_end|,
-        // but is not necessary since splice frames covert the overlap there.
-      } else {
-        track_buffer->set_needs_random_access_point(true);
-        DVLOG(3) << "Dropping frame that is outside append window.";
-
-        if (!sequence_mode_) {
-          // This also triggers a discontinuity so we need to treat the next
-          // frames appended within the append window as if they were the
-          // beginning of a new segment.
-          *new_media_segment = true;
-        }
-
-        return true;
+    if (track_buffer->stream()->supports_partial_append_window_trimming() &&
+        HandlePartialAppendWindowTrimming(append_window_start,
+                                          append_window_end,
+                                          presentation_timestamp,
+                                          frame_end_timestamp,
+                                          frame)) {
+      // |frame| has been partially trimmed or had preroll added.

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

ditto of LegacyFrameProcessor comment: do the following here, too?
track_buffer->set_needs_random_access_point(true);
if (!sequence_mode_)
  *new_media_segment = true;

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

Blew out the else from below. Should be fine now?

+      decode_timestamp = frame->GetDecodeTimestamp();
+      presentation_timestamp = frame->timestamp();
+      frame_duration = frame->duration();

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

Since presentation_timestamp & frame_duration are being updated here, does
frame_end_timestamp need to be recomputed?

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

No, since the timestamp is moved forward by a value equal to that by which the
duration is shrunk.

[acolwell GONE FROM CHROMIUM, 2014/05/24 00:58:20]

ok. A comment or DCHECK here would be nice so that this is clear.

[DaleCurtis, 2014/05/27 23:59:32]

Done.

+    } else if (presentation_timestamp < append_window_start ||

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

I wonder if we should drop the else here. ISTM that if the partial code above
does its job right, then it should not trigger the code in this block to run.
That would at least make it easier to see that the partial code can't
accidentally violate what the spec requires.

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

Good point: I think that would address my
*new_media_segment/set_needs_random_access_point comments, too.

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

Seems reasonable.  Done.

+               frame_end_timestamp > append_window_end) {
+      track_buffer->set_needs_random_access_point(true);
+      DVLOG(3) << "Dropping frame that is outside append window.";
+
+      if (!sequence_mode_) {
+        // This also triggers a discontinuity so we need to treat the next
+        // frames appended within the append window as if they were the
+        // beginning of a new segment.
+        *new_media_segment = true;
       }
+
+      return true;
     }
 
     // 12. If the need random access point flag on track buffer equals true,