1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
media / gpu / frame_size_estimator.h [blame]
// 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_FRAME_SIZE_ESTIMATOR_H_
#define MEDIA_GPU_FRAME_SIZE_ESTIMATOR_H_
#include "base/time/time.h"
#include "media/gpu/exponential_moving_average.h"
#include "media/gpu/media_gpu_export.h"
namespace media {
// An encoded frame size estimator.
// The estimator maintains the history of intermediate values (qp_size_value)
// that are proportional to encoded frame size and QP, and inversely
// proportional to the QP ratio of the previous and the current frame
// (delta_q_step_factor). The QP is converted to Q step value that has linear
// dependency to the encoded frame size.
//
// q_step = 5 / 8 * 2^(qp / 6)
//
// delta_q_step_factor = q_step_prev / q_step
//
// qp_size_value = q_step * frame_bytes / delta_q_step_factor
//
// The prediction of the encoded frame size is based on average values of
// qp_size_value and qp_size_correction. The qp_size_correction is the
// difference between actual encoded bytes and the predicted value.
//
// qp_size_correction = frame_bytes -
// qp_size_value * delta_q_step_factor / q_step
//
// pred_frame_bytes =
// qp_size_value * delta_q_step_factor / q_step + qp_size_correction
//
// In the inverse estimation process, the QP value is estimated for the given
// encoded frame size and the QP of the previous frame.
//
// q_step =
// sqrt(qp_size_value * q_step_prev / (frame_bytes + qp_size_correction))
//
// qp = 6 * log2(q_step / (5 / 8))
class MEDIA_GPU_EXPORT FrameSizeEstimator {
public:
FrameSizeEstimator(base::TimeDelta max_window_size,
float initial_qp_size,
float initial_size_correction);
~FrameSizeEstimator();
FrameSizeEstimator(const FrameSizeEstimator& other) = delete;
FrameSizeEstimator& operator=(const FrameSizeEstimator& other) = delete;
float qp_size_mean() const { return qp_size_stats_.mean(); }
float size_correction_mean() const { return size_correction_stats_.mean(); }
// Estimates encoded frame size for the given `qp` and `qp_prev`, based on the
// stats of the previous frames. In usual encoding scenario, the current
// QP is unknown at this point, but the estimate of the QP parameter is used
// instead.
size_t Estimate(uint32_t qp, uint32_t qp_prev) const;
// The Inverse Estimate is a reverse operation in frame size estimation where
// the QP value of the current frame is evaluated from the stats of the
// previously encoded frames and the encoded frame size.
uint32_t InverseEstimate(size_t target_frame_bytes, uint32_t qp_prev) const;
// Updates the frame size estimator state with the real encoded frame size and
// with the parameters used for video frame encoding.
void Update(size_t frame_bytes,
uint32_t qp,
uint32_t qp_prev,
base::TimeDelta elapsed_time);
void UpdateMaxWindowSize(base::TimeDelta max_window_size);
private:
ExponentialMovingAverage qp_size_stats_;
ExponentialMovingAverage size_correction_stats_;
};
} // namespace media
#endif // MEDIA_GPU_FRAME_SIZE_ESTIMATOR_H_