media/cast/sender/vp8_encoder.h

// 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.

#ifndef MEDIA_CAST_SENDER_CODECS_VP8_VP8_ENCODER_H_
#define MEDIA_CAST_SENDER_CODECS_VP8_VP8_ENCODER_H_

#include "base/basictypes.h"
#include "base/memory/scoped_ptr.h"
#include "base/threading/thread_checker.h"
#include "media/cast/cast_config.h"
#include "media/cast/sender/software_video_encoder.h"
#include "third_party/libvpx/source/libvpx/vpx/vpx_encoder.h"
#include "ui/gfx/geometry/size.h"

namespace media {
class VideoFrame;
}

namespace media {
namespace cast {

class Vp8Encoder : public SoftwareVideoEncoder {
 public:
  explicit Vp8Encoder(const VideoSenderConfig& video_config);

  ~Vp8Encoder() override;

  // SoftwareVideoEncoder implementations.
  void Initialize() override;
  void Encode(const scoped_refptr<media::VideoFrame>& video_frame,
              const base::TimeTicks& reference_time,
              EncodedFrame* encoded_frame) override;
  void UpdateRates(uint32 new_bitrate) override;
  void GenerateKeyFrame() override;
  void LatestFrameIdToReference(uint32 frame_id) override;

 private:
  enum { kNumberOfVp8VideoBuffers = 3 };

  enum Vp8Buffers {
    kAltRefBuffer = 0,
    kGoldenBuffer = 1,
    kLastBuffer = 2,
    kNoBuffer = 3  // Note: must be last.
  };

  enum Vp8BufferState {
    kBufferStartState,
    kBufferSent,
    kBufferAcked
  };

  struct BufferState {
    uint32 frame_id;
    Vp8BufferState state;
  };

  bool is_initialized() const {
    // ConfigureForNewFrameSize() sets the timebase denominator value to
    // non-zero if the encoder is successfully initialized, and it is zero
    // otherwise.
    return config_.g_timebase.den != 0;
  }

  // If the |encoder_| is live, attempt reconfiguration to allow it to encode
  // frames at a new |frame_size|.  Otherwise, tear it down and re-create a new
  // |encoder_| instance.
  void ConfigureForNewFrameSize(const gfx::Size& frame_size);

  // Calculate which next Vp8 buffers to update with the next frame.
  Vp8Buffers GetNextBufferToUpdate();

  // Get encoder flags for our referenced encoder buffers.
  // Return which previous frame to reference.
  uint32 GetCodecReferenceFlags(vpx_codec_flags_t* flags);

  // Get encoder flags for our encoder buffers to update with next frame.
  void GetCodecUpdateFlags(Vp8Buffers buffer_to_update,
                           vpx_codec_flags_t* flags);

  const VideoSenderConfig cast_config_;
  const bool use_multiple_video_buffers_;

  // VP8 internal objects.  These are valid for use only while is_initialized()
  // returns true.
  vpx_codec_enc_cfg_t config_;
  vpx_codec_ctx_t encoder_;

  // Set to true to request the next frame emitted by Vp8Encoder be a key frame.
  bool key_frame_requested_;

  // Saves the current bitrate setting, for when the |encoder_| is reconfigured
  // for different frame sizes.
  int bitrate_kbit_;

  // The |VideoFrame::timestamp()| of the last encoded frame.  This is used to
  // predict the duration of the next frame.
  base::TimeDelta last_frame_timestamp_;

  // The last encoded frame's ID.
  uint32 last_encoded_frame_id_;

  // Used to track which buffers are old enough to be re-used.
  uint32 last_acked_frame_id_;

  // Used by GetNextBufferToUpdate() to track how many consecutive times the
  // newest buffer had to be overwritten.
  int undroppable_frames_;

  // Tracks the lifecycle and dependency state of each of the three buffers.
  BufferState buffer_state_[kNumberOfVp8VideoBuffers];

  // This is bound to the thread where Initialize() is called.
  base::ThreadChecker thread_checker_;

  DISALLOW_COPY_AND_ASSIGN(Vp8Encoder);
};

}  // namespace cast
}  // namespace media

#endif  // MEDIA_CAST_SENDER_CODECS_VP8_VP8_ENCODER_H_