media/capture: Adding WebmMuxer class and unittests

media/capture/webm_muxer.h

Index: media/capture/webm_muxer.h
diff --git a/media/capture/webm_muxer.h b/media/capture/webm_muxer.h
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+// 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.
+
+#ifndef MEDIA_FILTERS_LIBWEBM_MUXER_H_
+#define MEDIA_FILTERS_LIBWEBM_MUXER_H_
+
+#include <set>
+
+#include "base/callback.h"
+#include "base/gtest_prod_util.h"
+#include "base/numerics/safe_math.h"
+#include "base/threading/thread_checker.h"
+#include "base/time/time.h"
+#include "media/base/media_export.h"
+#include "third_party/libwebm/source/mkvmuxer.hpp"
+#include "ui/gfx/geometry/size.h"
+
+namespace media {
+
+// Adapter class to manage a WebM container, a simplified version of a Matroska
+// container [1], composed of an EBML header, and a single Segment including
+// at least a Track Section and a number of SimpleBlocks each containing a
+// single encoded video frame. WebM container has no Trailer.
+// Clients will push encoded VPx video frames one by one via OnEncodedVideo()
+// with indication of the Track they belong to, and libwebm will eventually ping
+// the WriteDataCB passed on contructor with the wrapped encoded data. All
+// operations must happen in a single thread, where WebmMuxer is created and
+// destroyed.
+// [1] http://www.matroska.org/technical/specs/index.html
+// TODO(mcasas): Add support for Audio muxing.
+class MEDIA_EXPORT WebmMuxer : public mkvmuxer::IMkvWriter {
+ public:
+  // Callback to be called when WebmMuxer is ready to write a chunk of data,
+  // either any file header or a SingleBlock. The chunk is described as a byte
+  // array and a byte length.
+  typedef base::Callback<void(const char*, size_t)> WriteDataCB;
+
+  explicit WebmMuxer(const WriteDataCB& write_data_callback);
+  ~WebmMuxer() override;
+
+  // Creates and adds a new video track. Called before receiving the first
+  // frame of a given Track, adds |frame_size| and |frame_rate| to the Segment
+  // info, although individual frames passed to OnEncodedVideo() can have any
+  // frame size.
+  void AddVideoTrack(uint32_t track_number,
+                     const gfx::Size& frame_size,
+                     double frame_rate);
+
+  // Adds a frame with |encoded_data.data()| to WebM Segment. |track_number| is
+  // a caller-side identifier and must have been AddVideoTrack()ed before.
+  // |timedelta| is a delta from UTC/WebM Epoch, 2001-01-01 00:00:00.

[miu, 2015/07/18 00:29:39]

Don't burden the client with the WebM epoch calculations.  Instead, and for
consistency with all other media code, this should be the media timestamp where
frame zero has a TimeDelta = zero.  (The next frame has a timestamp = 1sec /
frame_rate, and so on.)  If, internally, the timestamp has to be converted to
some kind of relative-to-WebM-epoch timestamp, you should do that translation
inside OnEncodedVideo().

It's not clear to me what mkvmuxer needs here.  I'll leave that to you to figure
out.  I noticed you're not setting info->set_date_utc() anymore?  If the date
info is irrelevant, perhaps you can just pass the timestamps directly into the
container w/o any relative-to-date translation?

[mcasas, 2015/07/20 16:25:15]

Done.
I think mkvmuxer only needs a monotonously increasing timestamp, and
is used for audio/video/text synch, especially for Live streams.

+  void OnEncodedVideo(uint32_t track_number,
+                      const std::string& encoded_data,
+                      const base::TimeDelta& timedelta,

[miu, 2015/07/18 00:29:39]

naming: Forgot to mention last round: s/timedelta/timestamp/ or
s/timedelta/media_timestamp/

[mcasas, 2015/07/20 16:25:15]

Done.

+                      bool keyframe);
+
+ private:
+  friend class WebmMuxerTest;
+  FRIEND_TEST_ALL_PREFIXES(WebmMuxerTest, AddVideoTrack);
+  FRIEND_TEST_ALL_PREFIXES(WebmMuxerTest, Write);
+  FRIEND_TEST_ALL_PREFIXES(WebmMuxerTest, OnEncodedVideoEmptyAndNormalFrames);
+  FRIEND_TEST_ALL_PREFIXES(WebmMuxerTest, OnEncodedVideoNormalFrames);
+
+  // IMkvWriter interface.
+  mkvmuxer::int32 Write(const void* buf, mkvmuxer::uint32 len) override;
+  mkvmuxer::int64 Position() const override;
+  mkvmuxer::int32 Position(mkvmuxer::int64 position) override;
+  bool Seekable() const override;
+  void ElementStartNotify(mkvmuxer::uint64 element_id,
+                          mkvmuxer::int64 position) override;
+
+  // Used to DCHECK that we are called on the correct thread.
+  base::ThreadChecker thread_checker_;
+
+  // Callback to dump written data as being called by libwebm.
+  const WriteDataCB write_data_callback_;
+
+  // Rolling counter of the position in bytes of the written goo.
+  base::CheckedNumeric<mkvmuxer::int64> position_;
+
+  // Owned pointer to the MkvMuxer active element.
+  const scoped_ptr<mkvmuxer::Segment> segment_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebmMuxer);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_FILTERS_LIBWEBM_MUXER_H_