1 /*
2 * Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
3 *
4 * Use of this source code is governed by a BSD-style license
5 * that can be found in the LICENSE file in the root of the source
6 * tree. An additional intellectual property rights grant can be found
7 * in the file PATENTS. All contributing project authors may
8 * be found in the AUTHORS file in the root of the source tree.
9 */
10
11 #include "common_video/h264/h264_common.h"
12
13 #include <cstdint>
14
15 namespace webrtc {
16 namespace H264 {
17
18 const uint8_t kNaluTypeMask = 0x1F;
19
FindNaluIndices(const uint8_t * buffer,size_t buffer_size)20 std::vector<NaluIndex> FindNaluIndices(const uint8_t* buffer,
21 size_t buffer_size) {
22 // This is sorta like Boyer-Moore, but with only the first optimization step:
23 // given a 3-byte sequence we're looking at, if the 3rd byte isn't 1 or 0,
24 // skip ahead to the next 3-byte sequence. 0s and 1s are relatively rare, so
25 // this will skip the majority of reads/checks.
26 std::vector<NaluIndex> sequences;
27 if (buffer_size < kNaluShortStartSequenceSize)
28 return sequences;
29
30 static_assert(kNaluShortStartSequenceSize >= 2,
31 "kNaluShortStartSequenceSize must be larger or equals to 2");
32 const size_t end = buffer_size - kNaluShortStartSequenceSize;
33 for (size_t i = 0; i < end;) {
34 if (buffer[i + 2] > 1) {
35 i += 3;
36 } else if (buffer[i + 2] == 1) {
37 if (buffer[i + 1] == 0 && buffer[i] == 0) {
38 // We found a start sequence, now check if it was a 3 of 4 byte one.
39 NaluIndex index = {i, i + 3, 0};
40 if (index.start_offset > 0 && buffer[index.start_offset - 1] == 0)
41 --index.start_offset;
42
43 // Update length of previous entry.
44 auto it = sequences.rbegin();
45 if (it != sequences.rend())
46 it->payload_size = index.start_offset - it->payload_start_offset;
47
48 sequences.push_back(index);
49 }
50
51 i += 3;
52 } else {
53 ++i;
54 }
55 }
56
57 // Update length of last entry, if any.
58 auto it = sequences.rbegin();
59 if (it != sequences.rend())
60 it->payload_size = buffer_size - it->payload_start_offset;
61
62 return sequences;
63 }
64
ParseNaluType(uint8_t data)65 NaluType ParseNaluType(uint8_t data) {
66 return static_cast<NaluType>(data & kNaluTypeMask);
67 }
68
ParseRbsp(const uint8_t * data,size_t length)69 std::vector<uint8_t> ParseRbsp(const uint8_t* data, size_t length) {
70 std::vector<uint8_t> out;
71 out.reserve(length);
72
73 for (size_t i = 0; i < length;) {
74 // Be careful about over/underflow here. byte_length_ - 3 can underflow, and
75 // i + 3 can overflow, but byte_length_ - i can't, because i < byte_length_
76 // above, and that expression will produce the number of bytes left in
77 // the stream including the byte at i.
78 if (length - i >= 3 && !data[i] && !data[i + 1] && data[i + 2] == 3) {
79 // Two rbsp bytes.
80 out.push_back(data[i++]);
81 out.push_back(data[i++]);
82 // Skip the emulation byte.
83 i++;
84 } else {
85 // Single rbsp byte.
86 out.push_back(data[i++]);
87 }
88 }
89 return out;
90 }
91
WriteRbsp(const uint8_t * bytes,size_t length,rtc::Buffer * destination)92 void WriteRbsp(const uint8_t* bytes, size_t length, rtc::Buffer* destination) {
93 static const uint8_t kZerosInStartSequence = 2;
94 static const uint8_t kEmulationByte = 0x03u;
95 size_t num_consecutive_zeros = 0;
96 destination->EnsureCapacity(destination->size() + length);
97
98 for (size_t i = 0; i < length; ++i) {
99 uint8_t byte = bytes[i];
100 if (byte <= kEmulationByte &&
101 num_consecutive_zeros >= kZerosInStartSequence) {
102 // Need to escape.
103 destination->AppendData(kEmulationByte);
104 num_consecutive_zeros = 0;
105 }
106 destination->AppendData(byte);
107 if (byte == 0) {
108 ++num_consecutive_zeros;
109 } else {
110 num_consecutive_zeros = 0;
111 }
112 }
113 }
114
115 } // namespace H264
116 } // namespace webrtc
117