Line data    Source code

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