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
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
|
/*
* Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "common_video/h264/h264_common.h"
#include <cstdint>
namespace webrtc {
namespace H264 {
const uint8_t kNaluTypeMask = 0x1F;
std::vector<NaluIndex> FindNaluIndices(const uint8_t* buffer,
size_t buffer_size) {
// This is sorta like Boyer-Moore, but with only the first optimization step:
// given a 3-byte sequence we're looking at, if the 3rd byte isn't 1 or 0,
// skip ahead to the next 3-byte sequence. 0s and 1s are relatively rare, so
// this will skip the majority of reads/checks.
std::vector<NaluIndex> sequences;
if (buffer_size < kNaluShortStartSequenceSize)
return sequences;
static_assert(kNaluShortStartSequenceSize >= 2,
"kNaluShortStartSequenceSize must be larger or equals to 2");
const size_t end = buffer_size - kNaluShortStartSequenceSize;
for (size_t i = 0; i < end;) {
if (buffer[i + 2] > 1) {
i += 3;
} else if (buffer[i + 2] == 1) {
if (buffer[i + 1] == 0 && buffer[i] == 0) {
// We found a start sequence, now check if it was a 3 of 4 byte one.
NaluIndex index = {i, i + 3, 0};
if (index.start_offset > 0 && buffer[index.start_offset - 1] == 0)
--index.start_offset;
// Update length of previous entry.
auto it = sequences.rbegin();
if (it != sequences.rend())
it->payload_size = index.start_offset - it->payload_start_offset;
sequences.push_back(index);
}
i += 3;
} else {
++i;
}
}
// Update length of last entry, if any.
auto it = sequences.rbegin();
if (it != sequences.rend())
it->payload_size = buffer_size - it->payload_start_offset;
return sequences;
}
NaluType ParseNaluType(uint8_t data) {
return static_cast<NaluType>(data & kNaluTypeMask);
}
std::vector<uint8_t> ParseRbsp(const uint8_t* data, size_t length) {
std::vector<uint8_t> out;
out.reserve(length);
for (size_t i = 0; i < length;) {
// Be careful about over/underflow here. byte_length_ - 3 can underflow, and
// i + 3 can overflow, but byte_length_ - i can't, because i < byte_length_
// above, and that expression will produce the number of bytes left in
// the stream including the byte at i.
if (length - i >= 3 && !data[i] && !data[i + 1] && data[i + 2] == 3) {
// Two rbsp bytes.
out.push_back(data[i++]);
out.push_back(data[i++]);
// Skip the emulation byte.
i++;
} else {
// Single rbsp byte.
out.push_back(data[i++]);
}
}
return out;
}
void WriteRbsp(const uint8_t* bytes, size_t length, rtc::Buffer* destination) {
static const uint8_t kZerosInStartSequence = 2;
static const uint8_t kEmulationByte = 0x03u;
size_t num_consecutive_zeros = 0;
destination->EnsureCapacity(destination->size() + length);
for (size_t i = 0; i < length; ++i) {
uint8_t byte = bytes[i];
if (byte <= kEmulationByte &&
num_consecutive_zeros >= kZerosInStartSequence) {
// Need to escape.
destination->AppendData(kEmulationByte);
num_consecutive_zeros = 0;
}
destination->AppendData(byte);
if (byte == 0) {
++num_consecutive_zeros;
} else {
num_consecutive_zeros = 0;
}
}
}
} // namespace H264
} // namespace webrtc
|
