ts_section_pmt.cc

// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
 
#include <packager/media/formats/mp2t/ts_section_pmt.h>
 
#include <vector>
 
#include <absl/log/log.h>
 
#include <packager/media/base/bit_reader.h>
#include <packager/media/formats/mp2t/mp2t_common.h>
#include <packager/media/formats/mp2t/ts_audio_type.h>
#include <packager/media/formats/mp2t/ts_stream_type.h>
 
namespace shaka {
namespace media {
namespace mp2t {
 
namespace {
 
const int kISO639LanguageDescriptor = 0x0A;
const int kMaximumBitrateDescriptor = 0x0E;
const int kTeletextDescriptor = 0x56;
const int kSubtitlingDescriptor = 0x59;
 
}  // namespace
 
TsSectionPmt::TsSectionPmt(const RegisterPesCb& register_pes_cb)
    : register_pes_cb_(register_pes_cb) {}
 
TsSectionPmt::~TsSectionPmt() {}
 
bool TsSectionPmt::ParsePsiSection(BitReader* bit_reader) {
  // Read up to |last_section_number|.
  int table_id;
  int section_syntax_indicator;
  int dummy_zero;
  int reserved;
  int section_length;
  int program_number;
  int version_number;
  int current_next_indicator;
  int section_number;
  int last_section_number;
  RCHECK(bit_reader->ReadBits(8, &table_id));
  RCHECK(bit_reader->ReadBits(1, &section_syntax_indicator));
  RCHECK(bit_reader->ReadBits(1, &dummy_zero));
  RCHECK(bit_reader->ReadBits(2, &reserved));
  RCHECK(bit_reader->ReadBits(12, &section_length));
  int section_start_marker = static_cast<int>(bit_reader->bits_available()) / 8;
 
  RCHECK(bit_reader->ReadBits(16, &program_number));
  RCHECK(bit_reader->ReadBits(2, &reserved));
  RCHECK(bit_reader->ReadBits(5, &version_number));
  RCHECK(bit_reader->ReadBits(1, &current_next_indicator));
  RCHECK(bit_reader->ReadBits(8, &section_number));
  RCHECK(bit_reader->ReadBits(8, &last_section_number));
 
  // Perform a few verifications:
  // - table ID should be 2 for a PMT.
  // - section_syntax_indicator should be one.
  // - section length should not exceed 1021.
  RCHECK(table_id == 0x2);
  RCHECK(section_syntax_indicator);
  RCHECK(!dummy_zero);
  RCHECK(section_length <= 1021);
  RCHECK(section_number == 0);
  RCHECK(last_section_number == 0);
 
  // Read the end of the fixed length section.
  int pcr_pid;
  int program_info_length;
  RCHECK(bit_reader->ReadBits(3, &reserved));
  RCHECK(bit_reader->ReadBits(13, &pcr_pid));
  RCHECK(bit_reader->ReadBits(4, &reserved));
  RCHECK(bit_reader->ReadBits(12, &program_info_length));
  RCHECK(program_info_length < 1024);
 
  // Read the program info descriptor.
  // Defined in section 2.6 of ISO-13818.
  RCHECK(bit_reader->SkipBits(8 * program_info_length));
 
  // Read the ES description table.
  // The end of the PID map if 4 bytes away from the end of the section
  // (4 bytes = size of the CRC).
  int pid_map_end_marker = section_start_marker - section_length + 4;
  struct Info {
    int pid_es;
    TsStreamType stream_type;
    const uint8_t* descriptor;
    size_t descriptor_length;
    std::string lang;
    uint32_t max_bitrate;
    TsAudioType audio_type;
  };
  std::vector<Info> pid_info;
  while (static_cast<int>(bit_reader->bits_available()) >
         8 * pid_map_end_marker) {
    TsStreamType stream_type;
    int pid_es;
    size_t es_info_length;
    RCHECK(bit_reader->ReadBits(8, &stream_type));
    RCHECK(bit_reader->SkipBits(3));  // reserved
    RCHECK(bit_reader->ReadBits(13, &pid_es));
    RCHECK(bit_reader->ReadBits(4, &reserved));
    RCHECK(bit_reader->ReadBits(12, &es_info_length));
    const uint8_t* descriptor = bit_reader->current_byte_ptr();
 
    // Do not register the PID right away.
    // Wait for the end of the section to be fully parsed
    // to make sure there is no error.
    pid_info.push_back({pid_es, stream_type, descriptor, es_info_length, "", 0,
                        TsAudioType::kUndefined});
 
    // Read the ES info descriptors.
    // Defined in section 2.6 of ISO-13818.
    uint8_t descriptor_tag;
    uint8_t descriptor_length;
 
    while (es_info_length) {
      RCHECK(bit_reader->ReadBits(8, &descriptor_tag));
      RCHECK(bit_reader->ReadBits(8, &descriptor_length));
      es_info_length -= 2;
 
      // See ETSI EN 300 468 Section 6.1
      if (stream_type == TsStreamType::kPesPrivateData) {
        switch (descriptor_tag) {
          case kTeletextDescriptor:
            pid_info.back().stream_type = TsStreamType::kTeletextSubtitles;
            break;
          case kSubtitlingDescriptor:
            pid_info.back().stream_type = TsStreamType::kDvbSubtitles;
            break;
          default:
            break;
        }
      } else if (descriptor_tag == kISO639LanguageDescriptor &&
                 descriptor_length >= 4) {
        // See section 2.6.19 of ISO-13818
        // Descriptor can contain 0..N language defintions,
        // we process only the first one
        RCHECK(es_info_length >= 4);
 
        char lang[3];
        RCHECK(bit_reader->ReadBits(8, &lang[0]));  // ISO_639_language_code
        RCHECK(bit_reader->ReadBits(8, &lang[1]));
        RCHECK(bit_reader->ReadBits(8, &lang[2]));
        RCHECK(bit_reader->ReadBits(8, &pid_info.back().audio_type));
        pid_info.back().lang = std::string(lang, 3);
 
        es_info_length -= 4;
        descriptor_length -= 4;
      } else if (descriptor_tag == kMaximumBitrateDescriptor &&
                 descriptor_length >= 3) {
        // See section 2.6.25 of ISO-13818
        RCHECK(es_info_length >= 3);
 
        uint32_t max_bitrate;
        RCHECK(bit_reader->SkipBits(2));  // reserved
        RCHECK(bit_reader->ReadBits(22, &max_bitrate));
        // maximum bitrate is stored in units of 50 bytes per second
        pid_info.back().max_bitrate = 50 * 8 * max_bitrate;
 
        es_info_length -= 3;
        descriptor_length -= 3;
      }
 
      RCHECK(bit_reader->SkipBits(8 * descriptor_length));
      es_info_length -= descriptor_length;
    }
 
    RCHECK(bit_reader->SkipBytes(es_info_length));
  }
 
  // Read the CRC.
  int crc32;
  RCHECK(bit_reader->ReadBits(32, &crc32));
 
  // Once the PMT has been proved to be correct, register the PIDs.
  for (auto& info : pid_info) {
    register_pes_cb_(info.pid_es, info.stream_type, info.max_bitrate, info.lang,
                     info.audio_type, info.descriptor, info.descriptor_length);
  }
 
  return true;
}
 
void TsSectionPmt::ResetPsiSection() {}
 
}  // namespace mp2t
}  // namespace media
}  // namespace shaka