[cros] Implement WebM encoder/muxer for animated avatar capture.

chrome/browser/chromeos/webm_encoder.h

+// Copyright (c) 2012 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 CHROME_BROWSER_CHROMEOS_WEBM_ENCODER_H_
+#define CHROME_BROWSER_CHROMEOS_WEBM_ENCODER_H_
+
+#include <stack>
+#include <stdio.h>
+
+#include "base/file_path.h"
+#include "base/memory/scoped_ptr.h"
+#include "chrome/browser/chromeos/ebml_writer.h"
+
+extern "C" {
+#define VPX_CODEC_DISABLE_COMPAT 1
+#include "third_party/libvpx/libvpx.h"
+}
+
+class FilePath;
+class SkBitmap;
+
+namespace chromeos {
+
+// WebM encoder using libvpx. Currently only supports one-pass, constant bitrate
+// encoding of short files consisting of a single video track. Seek info and
+// cues are not supported, so generated .webm file does not strictly adhere to
+// WebM standard (http://www.webmproject.org/code/specs/container/).
+class WebmEncoder {
+ public:
+  // Create new instance for writing to |output_path|. If |realtime| is |true|,
+  // uses realtime deadline, otherwise - "good quality" deadline.
+  WebmEncoder(const FilePath& output_path, unsigned bitrate, bool realtime);
+
+  // Encodes video from a Nx(N*M) sprite, having M frames of size NxN with FPS
+  // |fps_n/fps_d|. Must be called on a thread that allows IO.

[Nikita (slow), 2012/07/18 16:23:05]

nit: allows disk IO

[Ivan Korotkov, 2012/07/20 09:09:29]

Done.

+  void EncodeFromSprite(const SkBitmap& sprite, int fps_n, int fps_d);
+
+ private:
+  // Write global WebM header and starts a single video track.

[Nikita (slow), 2012/07/18 16:23:05]

nit: Writes

[Ivan Korotkov, 2012/07/20 09:09:29]

Done.

+  void WriteWebmHeader();
+  // Writes VPX packet to output file.

[Nikita (slow), 2012/07/18 16:23:05]

nit: insert empty line

[Ivan Korotkov, 2012/07/20 09:09:29]

Done.

+  void WriteWebmBlock(const vpx_codec_cx_pkt_t* packet);
+  // Finished video track and closes output file.

[Nikita (slow), 2012/07/18 16:23:05]

nit: insert empty line
nit: Finishes

[Ivan Korotkov, 2012/07/20 09:09:29]

Done.

+  void WriteWebmFooter();
+
+  // Starts a new WebM sub-element of given type. Those can be nested.
+  void StartSubElement(unsigned long class_id);
+  // Closes current top-level sub-element.

[Nikita (slow), 2012/07/18 16:23:05]

nit: insert empty line

[Ivan Korotkov, 2012/07/20 09:09:29]

Done.

+  void EndSubElement();
+
+  // libmkv callbacks.
+  void EbmlWrite(const void* buffer, unsigned long len);
+  void EbmlSerialize(const void* buffer, int buffer_size, unsigned long len);
+
+  template <typename T>
+  void EbmlSerializeHelper(const T* buffer, unsigned long len);
+
+  // Video dimensions and FPS.
+  size_t width_;
+  size_t height_;
+  vpx_rational_t fps_;
+
+  // Single I420 frame data.
+  scoped_array<uint8> yuv_frame_;
+
+  // VPX config in use.
+  vpx_codec_enc_cfg_t config_;
+
+  // VPX parameters.
+  unsigned bitrate_;
+  unsigned long deadline_;
+
+  // EbmlWriter context.
+  EbmlGlobal ebml_writer_;
+
+  // Stack with start offsets of currently open sub-elements.
+  std::stack<long int> ebml_sub_elements_;
+
+  FilePath output_path_;
+  FILE* output_;
+};
+
+}  // namespace chromeos
+
+#endif  // CHROME_BROWSER_CHROMEOS_WEBM_ENCODER_H_