media/formats/mp2t/ts_section_pat.cc

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #include "media/formats/mp2t/ts_section_pat.h"
   6
   7 #include <vector>
   8
   9 #include "base/logging.h"
  10 #include "media/base/bit_reader.h"
  11 #include "media/formats/mp2t/mp2t_common.h"
  12
  13 namespace media {
  14 namespace mp2t {
  15
  16 TsSectionPat::TsSectionPat(const RegisterPmtCb& register_pmt_cb)
  17     : register_pmt_cb_(register_pmt_cb),
  18       version_number_(-1) {
  19 }
  20
  21 TsSectionPat::~TsSectionPat() {
  22 }
  23
  24 bool TsSectionPat::ParsePsiSection(BitReader* bit_reader) {
  25   // Read the fixed section length.
  26   int table_id;
  27   int section_syntax_indicator;
  28   int dummy_zero;
  29   int reserved;
  30   int section_length;
  31   int transport_stream_id;
  32   int version_number;
  33   int current_next_indicator;
  34   int section_number;
  35   int last_section_number;
  36   RCHECK(bit_reader->ReadBits(8, &table_id));
  37   RCHECK(bit_reader->ReadBits(1, &section_syntax_indicator));
  38   RCHECK(bit_reader->ReadBits(1, &dummy_zero));
  39   RCHECK(bit_reader->ReadBits(2, &reserved));
  40   RCHECK(bit_reader->ReadBits(12, &section_length));
  41   RCHECK(section_length >= 5);
  42   RCHECK(section_length <= 1021);
  43   RCHECK(bit_reader->ReadBits(16, &transport_stream_id));
  44   RCHECK(bit_reader->ReadBits(2, &reserved));
  45   RCHECK(bit_reader->ReadBits(5, &version_number));
  46   RCHECK(bit_reader->ReadBits(1, &current_next_indicator));
  47   RCHECK(bit_reader->ReadBits(8, &section_number));
  48   RCHECK(bit_reader->ReadBits(8, &last_section_number));
  49   section_length -= 5;
  50
  51   // Perform a few verifications:
  52   // - Table ID should be 0 for a PAT.
  53   // - section_syntax_indicator should be one.
  54   // - section length should not exceed 1021
  55   RCHECK(table_id == 0x0);
  56   RCHECK(section_syntax_indicator);
  57   RCHECK(!dummy_zero);
  58
  59   // Both the program table and the CRC have a size multiple of 4.
  60   // Note for pmt_pid_count: minus 4 to account for the CRC.
  61   RCHECK((section_length % 4) == 0);
  62   int pmt_pid_count = (section_length - 4) / 4;
  63
  64   // Read the variable length section: program table & crc.
  65   std::vector<int> program_number_array(pmt_pid_count);
  66   std::vector<int> pmt_pid_array(pmt_pid_count);
  67   for (int k = 0; k < pmt_pid_count; k++) {
  68     int reserved;
  69     RCHECK(bit_reader->ReadBits(16, &program_number_array[k]));
  70     RCHECK(bit_reader->ReadBits(3, &reserved));
  71     RCHECK(bit_reader->ReadBits(13, &pmt_pid_array[k]));
  72   }
  73   int crc32;
  74   RCHECK(bit_reader->ReadBits(32, &crc32));
  75
  76   // Just ignore the PAT if not applicable yet.
  77   if (!current_next_indicator) {
  78     DVLOG(1) << "Not supported: received a PAT not applicable yet";
  79     return true;
  80   }
  81
  82   // Ignore the program table if it hasn't changed.
  83   if (version_number == version_number_)
  84     return true;
  85
  86   // Both the MSE and the HLS spec specifies that TS streams should convey
  87   // exactly one program.
  88   if (pmt_pid_count > 1) {
  89     DVLOG(1) << "Multiple programs detected in the Mpeg2 TS stream";
  90     return false;
  91   }
  92
  93   // Can now register the PMT.
  94 #if !defined(NDEBUG)
  95   int expected_version_number = version_number;
  96   if (version_number_ >= 0)
  97     expected_version_number = (version_number_ + 1) % 32;
  98   DVLOG_IF(1, version_number != expected_version_number)
  99       << "Unexpected version number: "
 100       << version_number << " vs " << version_number_;
 101 #endif
 102   for (int k = 0; k < pmt_pid_count; k++) {
 103     if (program_number_array[k] != 0) {
 104       // Program numbers different from 0 correspond to PMT.
 105       register_pmt_cb_.Run(program_number_array[k], pmt_pid_array[k]);
 106       // Even if there are multiple programs, only one can be supported now.
 107       // HLS: "Transport Stream segments MUST contain a single MPEG-2 Program."
 108       break;
 109     }
 110   }
 111   version_number_ = version_number;
 112
 113   return true;
 114 }
 115
 116 void TsSectionPat::ResetPsiSection() {
 117   version_number_ = -1;
 118 }
 119
 120 }  // namespace mp2t
 121 }  // namespace media
 122