Implement core of compliant MediaSource coded frame processing

media/filters/frame_processor.cc

+// Copyright 2014 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/frame_processor.h"
+
+#include "base/stl_util.h"
+#include "media/base/buffers.h"
+#include "media/base/stream_parser_buffer.h"
+
+namespace media {
+
+FrameProcessor::FrameProcessor(const UpdateDurationCB& update_duration_cb)
+    : group_start_timestamp_(kNoTimestamp()),
+      update_duration_cb_(update_duration_cb) {
+  DVLOG(2) << __FUNCTION__ << "()";
+  DCHECK(!update_duration_cb.is_null());
+}
+
+FrameProcessor::~FrameProcessor() {
+  DVLOG(2) << __FUNCTION__;
+}
+
+void FrameProcessor::SetSequenceMode(bool sequence_mode) {
+  DVLOG(2) << __FUNCTION__ << "(" << sequence_mode << ")";
+
+  // Per April 1, 2014 MSE spec editor's draft:
+  // https://dvcs.w3.org/hg/html-media/raw-file/d471a4412040/media-source/media-source.html#widl-SourceBuffer-mode
+  // Step 7: If the new mode equals "sequence", then set the group start
+  // timestamp to the group end timestamp.
+  if (sequence_mode) {
+    DCHECK(kNoTimestamp() != group_end_timestamp_);
+    group_start_timestamp_ = group_end_timestamp_;
+  }
+
+  // Step 8: Update the attribute to new mode.
+  sequence_mode_ = sequence_mode;
+}
+
+void FrameProcessor::SetGroupStartTimestampIfInSequenceMode(
+    base::TimeDelta timestamp_offset) {
+  DVLOG(2) << __FUNCTION__ << "(" << timestamp_offset.InSecondsF() << ")";
+  DCHECK(kNoTimestamp() != timestamp_offset);
+  if (sequence_mode_)
+    group_start_timestamp_ = timestamp_offset;
+}
+
+bool FrameProcessor::ProcessFrames(
+    const StreamParser::BufferQueue& audio_buffers,
+    const StreamParser::BufferQueue& video_buffers,
+    const StreamParser::TextBufferQueueMap& text_map,
+    base::TimeDelta append_window_start,
+    base::TimeDelta append_window_end,
+    bool* new_media_segment,
+    base::TimeDelta* timestamp_offset) {
+  StreamParser::BufferQueue frames;
+  if (!MergeBufferQueues(audio_buffers, video_buffers, text_map, &frames)) {
+    DVLOG(2) << "Parse error discovered while merging parser's buffers";
+    return false;
+  }
+
+  DCHECK(!frames.empty());
+
+  // Implements the coded frame processing algorithm's outer loop for step 1.
+  // Note that ProcessFrame() implements an inner loop for a single frame that
+  // handles "jump to the Loop Top step to restart processing of the current
+  // coded frame" per April 1, 2014 MSE spec editor's draft:
+  // https://dvcs.w3.org/hg/html-media/raw-file/d471a4412040/media-source/media-source.html#sourcebuffer-coded-frame-processing
+  // 1. For each coded frame in the media segment run the following steps:
+  for (StreamParser::BufferQueue::const_iterator frames_itr = frames.begin();
+       frames_itr != frames.end(); ++frames_itr) {
+    if (!ProcessFrame(*frames_itr, append_window_start, append_window_end,
+                      timestamp_offset, new_media_segment)) {
+      return false;
+    }
+  }
+
+  // 2. - 4. Are handled by the WebMediaPlayer / Pipeline / Media Element.
+
+  // Step 5:
+  update_duration_cb_.Run(group_end_timestamp_);
+
+  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) {
+  // 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:

[acolwell GONE FROM CHROMIUM, 2014/05/08 17:32:22]

Please make sure you have a bug filed to track updating the algorithm to contain
the changes made in the April 29th version.

[wolenetz, 2014/05/08 19:59:02]

Good point. I filed bug 371499 and referenced it now from the
auto_update_timestamp_offset_ definition in SourceState.

+  // https://dvcs.w3.org/hg/html-media/raw-file/d471a4412040/media-source/media-source.html#sourcebuffer-coded-frame-processing
+
+  while (true) {
+    // 1. Loop Top: Let presentation timestamp be a double precision floating
+    //    point representation of the coded frame's presentation timestamp in
+    //    seconds.
+    // 2. Let decode timestamp be a double precision floating point
+    //    representation of the coded frame's decode timestamp in seconds.
+    // 3. Let frame duration be a double precision floating point representation
+    //    of the coded frame's duration in seconds.
+    // We use base::TimeDelta instead of double.
+    base::TimeDelta presentation_timestamp = frame->timestamp();
+    base::TimeDelta decode_timestamp = frame->GetDecodeTimestamp();
+    base::TimeDelta frame_duration = frame->duration();
+
+    DVLOG(3) << __FUNCTION__ << ": Processing frame "
+             << "Type=" << frame->type()
+             << ", TrackID=" << frame->track_id()
+             << ", PTS=" << presentation_timestamp.InSecondsF()
+             << ", DTS=" << decode_timestamp.InSecondsF()
+             << ", DUR=" << frame_duration.InSecondsF();
+
+    // Sanity check the timestamps.
+    if (presentation_timestamp < base::TimeDelta()) {
+      DVLOG(2) << __FUNCTION__ << ": Negative or unknown frame PTS: "
+               << presentation_timestamp.InSecondsF();
+      return false;
+    }
+    if (decode_timestamp < base::TimeDelta()) {
+      DVLOG(2) << __FUNCTION__ << ": Negative or unknown frame DTS: "
+               << decode_timestamp.InSecondsF();
+      return false;
+    }
+    if (decode_timestamp > presentation_timestamp) {
+      // TODO(wolenetz): Determine whether DTS>PTS should really be allowed. See
+      // http://crbug.com/354518.
+      DVLOG(2) << __FUNCTION__ << ": WARNING: Frame DTS("
+               << decode_timestamp.InSecondsF() << ") > PTS("
+               << presentation_timestamp.InSecondsF() << ")";
+    }
+
+    // TODO(acolwell/wolenetz): All stream parsers must emit valid (positive)
+    // frame durations. For now, we allow non-negative frame duration.
+    // See http://crbug.com/351166.
+    if (frame_duration == kNoTimestamp()) {
+      DVLOG(2) << __FUNCTION__ << ": Frame missing duration (kNoTimestamp())";
+      return false;
+    }
+    if (frame_duration <  base::TimeDelta()) {
+      DVLOG(2) << __FUNCTION__ << ": Frame duration negative: "
+               << frame_duration.InSecondsF();
+      return false;
+    }
+
+    // 4. If mode equals "sequence" and group start timestamp is set, then run
+    //    the following steps:
+    if (sequence_mode_ && group_start_timestamp_ != kNoTimestamp()) {
+      // 4.1. Set timestampOffset equal to group start timestamp -
+      //      presentation timestamp.
+      *timestamp_offset = group_start_timestamp_ - presentation_timestamp;
+
+      DVLOG(3) << __FUNCTION__ << ": updated timestampOffset is now "
+               << timestamp_offset->InSecondsF();
+
+      // 4.2. Set group end timestamp equal to group start timestamp.
+      group_end_timestamp_ = group_start_timestamp_;
+
+      // 4.3. Set the need random access point flag on all track buffers to
+      //      true.
+      SetAllTrackBuffersNeedRandomAccessPoint();
+
+      // 4.4. Unset group start timestamp.
+      group_start_timestamp_ = kNoTimestamp();
+    }
+
+    // 5. If timestampOffset is not 0, then run the following steps:
+    if (*timestamp_offset != base::TimeDelta()) {
+      // 5.1. Add timestampOffset to the presentation timestamp.
+      // Note: |frame| PTS is only updated if it survives processing.
+      presentation_timestamp += *timestamp_offset;
+
+      // 5.2. Add timestampOffset to the decode timestamp.
+      // Frame DTS is only updated if it survives processing.
+      decode_timestamp += *timestamp_offset;
+    }
+
+    // 6. Let track buffer equal the track buffer that the coded frame will be
+    //    added to.
+
+    // Remap audio and video track types to their special singleton identifiers.
+    StreamParser::TrackId track_id = kAudioTrackId;
+    switch (frame->type()) {
+      case DemuxerStream::AUDIO:
+        break;
+      case DemuxerStream::VIDEO:
+        track_id = kVideoTrackId;
+        break;
+      case DemuxerStream::TEXT:
+        track_id = frame->track_id();
+        break;
+      case DemuxerStream::UNKNOWN:
+      case DemuxerStream::NUM_TYPES:
+        DCHECK(false) << ": Invalid frame type " << frame->type();
+        return false;
+    }
+
+    MseTrackBuffer* track_buffer = FindTrack(track_id);
+    if (!track_buffer) {
+      DVLOG(2) << __FUNCTION__ << ": Unknown track: type=" << frame->type()
+               << ", frame processor track id=" << track_id
+               << ", parser track id=" << frame->track_id();
+      return false;
+    }
+
+    // 7. If last decode timestamp for track buffer is set and decode timestamp
+    //    is less than last decode timestamp
+    //    OR
+    //    If last decode timestamp for track buffer is set and the difference
+    //    between decode timestamp and last decode timestamp is greater than 2
+    //    times last frame duration:
+    base::TimeDelta last_decode_timestamp =
+        track_buffer->last_decode_timestamp();
+    if (last_decode_timestamp != kNoTimestamp()) {
+      base::TimeDelta dts_delta = decode_timestamp - last_decode_timestamp;
+      if (dts_delta < base::TimeDelta() ||
+          dts_delta > 2 * track_buffer->last_frame_duration()) {
+        // 7.1. If mode equals "segments": Set group end timestamp to
+        //      presentation timestamp.
+        //      If mode equals "sequence": Set group start timestamp equal to
+        //      the group end timestamp.
+        if (!sequence_mode_) {
+          group_end_timestamp_ = presentation_timestamp;
+        } else {
+          DCHECK(kNoTimestamp() != group_end_timestamp_);
+          group_start_timestamp_ = group_end_timestamp_;
+        }
+
+        // 7.2. - 7.5.:
+        Reset();
+
+        // This 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;
+
+        // 7.6. Jump to the Loop Top step above to restart processing of the
+        //      current coded frame.
+        DVLOG(3) << __FUNCTION__ << ": Discontinuity: reprocessing frame";
+        continue;
+      }
+    }
+
+    // 8. If the presentation timestamp or decode timestamp is less than the
+    // presentation start time, then run the end of stream algorithm with the
+    // error parameter set to "decode", and abort these steps.
+    if (presentation_timestamp < base::TimeDelta() ||
+        decode_timestamp < base::TimeDelta()) {
+      DVLOG(2) << __FUNCTION__
+               << ": frame PTS=" << presentation_timestamp.InSecondsF()
+               << " or DTS=" << decode_timestamp.InSecondsF()
+               << " negative after applying timestampOffset and handling any "
+               << " discontinuity";
+      return false;
+    }
+
+    // 9. Let frame end timestamp equal the sum of presentation timestamp and
+    //    frame duration.
+    base::TimeDelta frame_end_timestamp = presentation_timestamp +
+        frame_duration;
+
+    // 10.  If presentation timestamp is less than appendWindowStart, 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.
+    // Note: We keep the result of partial discard of a buffer that overlaps
+    //      |append_window_start| and does not end after |append_window_end|.
+    // 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.";
+
+        // 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,
+    //     then run the following steps:
+    if (track_buffer->needs_random_access_point()) {
+      // 12.1. If the coded frame is not a random access point, then drop the
+      //       coded frame and jump to the top of the loop to start processing
+      //       the next coded frame.
+      if (!frame->IsKeyframe()) {
+        DVLOG(3) << __FUNCTION__
+                 << ": Dropping frame that is not a random access point";
+        return true;
+      }
+
+      // 12.2. Set the need random access point flag on track buffer to false.
+      track_buffer->set_needs_random_access_point(false);
+    }
+
+    // We now have a processed buffer to append to the track buffer's stream.
+    // If it is the first in a new media segment or following a discontinuity,
+    // notify all the track buffers' streams that a new segment is beginning.
+    if (*new_media_segment) {
+      *new_media_segment = false;
+      NotifyNewMediaSegmentStarting(decode_timestamp);
+    }
+
+    DVLOG(3) << __FUNCTION__ << ": Sending processed frame to stream, "
+             << "PTS=" << presentation_timestamp.InSecondsF()
+             << ", DTS=" << decode_timestamp.InSecondsF();
+    frame->set_timestamp(presentation_timestamp);
+    frame->SetDecodeTimestamp(decode_timestamp);
+
+    // Steps 13-18:
+    // TODO(wolenetz): Collect and emit more than one buffer at a time, if
+    // possible. See http://crbug.com/371197.

[acolwell GONE FROM CHROMIUM, 2014/05/08 17:32:22]

Another part of this may entail refactoring SourceBufferStream to closer reflect
what is written in the spec and defer things like GC to run at a different time
like the spec indicates.

[wolenetz, 2014/05/08 19:59:02]

Good point. I've added your comment to crbug.com/371197 and updated this source
comment. That bug may eventually become split into more pieces (or get some
dependents) to track these potentially multiple concerns.

+    StreamParser::BufferQueue buffer_to_append;
+    buffer_to_append.push_back(frame);
+    track_buffer->stream()->Append(buffer_to_append);
+
+    // 19. Set last decode timestamp for track buffer to decode timestamp.
+    track_buffer->set_last_decode_timestamp(decode_timestamp);
+
+    // 20. Set last frame duration for track buffer to frame duration.
+    track_buffer->set_last_frame_duration(frame_duration);
+
+    // 21. If highest presentation timestamp for track buffer is unset or frame
+    //     end timestamp is greater than highest presentation timestamp, then
+    //     set highest presentation timestamp for track buffer to frame end
+    //     timestamp.
+    track_buffer->SetHighestPresentationTimestampIfIncreased(
+        frame_end_timestamp);
+
+    // 22. If frame end timestamp is greater than group end timestamp, then set
+    //     group end timestamp equal to frame end timestamp.
+    DCHECK(group_end_timestamp_ >= base::TimeDelta());
+    if (frame_end_timestamp > group_end_timestamp_)
+      group_end_timestamp_ = frame_end_timestamp;
+
+    return true;
+  }
+
+  NOTREACHED();
+  return false;
+}
+
+void FrameProcessor::SetAllTrackBuffersNeedRandomAccessPoint() {
+  for (TrackBufferMap::iterator itr = track_buffers_.begin();
+       itr != track_buffers_.end(); ++itr) {
+    itr->second->set_needs_random_access_point(true);
+  }
+}
+
+}  // namespace media