media/capture: Adding WebmMuxer class and unittests

media/filters/webm_muxer.cc

+// Copyright 2015 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/webm_muxer.h"
+
+#include "base/time/time.h"
+
+namespace media {
+
+WebmMuxer::WebmMuxer(const WriteDataCB& write_data_callback)
+    : write_data_callback_(write_data_callback),
+      time_start_(base::TimeTicks::Now()),
+      position_(0),
+      segment_(new mkvmuxer::Segment()) {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
+  segment_->Init(this);
+  segment_->set_mode(mkvmuxer::Segment::kLive);
+  segment_->OutputCues(false);
+
+  mkvmuxer::SegmentInfo* const info = segment_->GetSegmentInfo();
+  info->set_writing_app("Chrome");
+  info->set_muxing_app("Chrome");
+  // SegmentInfo::set_date_utc() is nanoseconds from 0:00 on January 1st, 2001.
+  base::Time utc_epoch;
+  base::Time::FromUTCString("1 Jan 2001 00:00:00.000", &utc_epoch);

[miu, 2015/07/16 01:46:25]

BTW--The media/PRESUBMIT.py script may cause commit problems if you use
base::Time.  An alternative would be:

  const base::TimeDelta webm_epoch = base::TimeTicks::UnixEpoch() +
base::TimeDelta::FromSeconds(978307200);
  ...
  info->set_date_utc(base::TimeTicks::Now() - webm_epoch).InMicroseconds() *
nanos_per_micro);

[mcasas, 2015/07/17 17:45:07]

Done.

+  DCHECK(!utc_epoch.is_null());
+  info->set_date_utc((base::Time::Now() - utc_epoch).InMicroseconds() *
+                     base::Time::kNanosecondsPerMicrosecond);
+}
+
+WebmMuxer::~WebmMuxer() {
+  DCHECK(thread_checker_.CalledOnValidThread());
+  DVLOG(3) << __FUNCTION__;
+  segment_->Finalize();
+}
+
+void WebmMuxer::OnEncodedVideo(int track_index,
+                               const std::string& encoded_data,
+                               const base::TimeTicks& timestamp,
+                               bool keyframe,
+                               const gfx::Size& frame_size,
+                               double frame_rate) {
+  DVLOG(3) << __FUNCTION__;
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  const int index_starting_from_one = track_index + 1;
+  // Add the video track the first time we see it.
+  if (track_indexes_.find(index_starting_from_one) == track_indexes_.end()) {
+    AddVideoTrack(frame_size, frame_rate, index_starting_from_one);
+    track_indexes_.insert(index_starting_from_one);
+  }
+
+  // Depending on segment->GetSegmentInfo()->timecode_scale(), timestamps are in
+  // milliseconds or microseconds. By default in milliseconds.
+  segment_->AddFrame(reinterpret_cast<const uint8_t*>(encoded_data.data()),
+                     encoded_data.size(),
+                     index_starting_from_one,
+                     (timestamp - time_start_).InMilliseconds(),

[miu, 2015/07/16 01:46:25]

InMicroseconds() please.  See comment below.

[mcasas, 2015/07/17 17:45:07]

Done.

+                     keyframe);
+}
+
+bool WebmMuxer::AddVideoTrack(const gfx::Size& frame_size,
+                              double frame_rate,
+                              int track_index_starting_from_one) {
+  DVLOG(3) << "AddVideoTrack: " << frame_size.ToString() << "@"
+           << frame_rate << "fps, index: " << track_index_starting_from_one;
+  DCHECK(thread_checker_.CalledOnValidThread());
+
+  segment_->AddVideoTrack(frame_size.width(), frame_size.height(),
+                          track_index_starting_from_one);
+  mkvmuxer::VideoTrack* const video_track =
+      reinterpret_cast<mkvmuxer::VideoTrack*>(
+          segment_->GetTrackByNumber(track_index_starting_from_one));
+  DCHECK(video_track);
+  video_track->set_codec_id(mkvmuxer::Tracks::kVp8CodecId);
+  DCHECK_EQ(video_track->crop_right(), 0ull);
+  DCHECK_EQ(video_track->crop_left(), 0ull);
+  DCHECK_EQ(video_track->crop_top(), 0ull);
+  DCHECK_EQ(video_track->crop_bottom(), 0ull);
+
+  video_track->set_frame_rate(frame_rate);
+  // Depending on segment->GetSegmentInfo()->timecode_scale(), timestamps are
+  // interpreted as milliseconds, microseconds, etc.
+  // By default it's is milliseconds, but DCHECK that.

[miu, 2015/07/16 01:46:25]

BTW--One of my pet peeves is truncating media timestamps to milliseconds.  Can
we set a microsecond timebase here?

[mcasas, 2015/07/17 17:45:07]

Done.

+  DCHECK_EQ(segment_->GetSegmentInfo()->timecode_scale(), 1000000ull);
+  video_track->set_default_duration(base::Time::kMillisecondsPerSecond /
+                                    frame_rate);
+
+  return true;
+}
+
+mkvmuxer::int32 WebmMuxer::Write(const void* buf, mkvmuxer::uint32 len) {
+  DVLOG(3) << __FUNCTION__ << " length=" << len;
+  DCHECK(thread_checker_.CalledOnValidThread());
+  write_data_callback_.Run(static_cast<const char*>(buf), len);

[miu, 2015/07/16 01:46:25]

Potential bug: If |len| is greater than 2^31-1, this will translate into a
negative number.

[mcasas, 2015/07/17 17:45:07]

Made them size_t in WriteDataCB etc.

+  position_ += len;
+  return 0;
+}
+
+mkvmuxer::int64 WebmMuxer::Position() const {
+  return position_.ValueOrDefault(0);

[miu, 2015/07/16 01:46:25]

Shouldn't this be ValueOrDie()?  Also, there's an implicit unsigned-to-signed
conversion here, so |position_| should probably be a CheckedNumeric<int64>.

[mcasas, 2015/07/17 17:45:07]

Done.

+}
+
+mkvmuxer::int32 WebmMuxer::Position(mkvmuxer::int64 position) {
+  // The stream is not Seekable() so indicate we cannot set the position.
+  return -1;
+}
+
+bool WebmMuxer::Seekable() const {
+  return false;
+}
+
+void WebmMuxer::ElementStartNotify(mkvmuxer::uint64 element_id,
+                                   mkvmuxer::int64 position) {
+  // This method gets pinged before items are sent to |write_data_callback_|.
+  DCHECK_GE(static_cast<uint64_t>(position), position_.ValueOrDefault(0))
+      << "Can't go back in a Live Mkv stream.";
+}
+
+}  // namespace media