chromium/media/gpu/h264_rate_controller.h

// Copyright 2023 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef MEDIA_GPU_H264_RATE_CONTROLLER_H_
#define MEDIA_GPU_H264_RATE_CONTROLLER_H_

#include <vector>

#include "base/moving_window.h"
#include "media/gpu/frame_size_estimator.h"
#include "media/gpu/hrd_buffer.h"
#include "media/gpu/media_gpu_export.h"
#include "media/video/video_encode_accelerator.h"

namespace media {

struct MEDIA_GPU_EXPORT H264RateControllerLayerSettings { … };

struct MEDIA_GPU_EXPORT H264RateControllerSettings { … };

// H264RateController class implements a rate control algorithm for H.264 video
// encoder. The algorithm adjusts the QP for each frame, aiming to keep the
// video stream bitrate close to the target bitrate. The controller supports
// up to two temporal layers, each with its own HRD buffer. The HRD buffer
// stores the encoded frames from the current layer and all the lower layers
// that it depens on.
//
// The prediction of the QP parameter for intra encoded frames is based on the
// R-D model, using the expected size of the encoded frame as an input.
// For inter encoded frames, the QP is calculated based on the long-term and
// short-term statistics of the estamated QP and frame size, the prediction
// error of the frame size prediction for the previously encoded frames,
// and the HRD buffer fullness.
//
// The QP values used for encoding the inter predicted frames (P frames) are
// estimated from the statistics of the previous frames and the expected frame
// size. The estimation engine holds the short-term and long-term statistics for
// each temporal layer. The QP is further modified according to the HRD buffer
// fullness and the limits of the QP range. If rate controller is configured for
// the fixed delta QP between layers (Fixed Delta QP mode), the QP for the
// current layer is calculated by adding a constant value to the previous
// layer's QP.
class MEDIA_GPU_EXPORT H264RateController { … };

}  // namespace media

#endif  // MEDIA_GPU_H264_RATE_CONTROLLER_H_