ts_section_pat.cc revision 5d1f7b1de12d16ceb2c938c56701a3e8bfa558f7 
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
13namespace media {
14namespace mp2t {
15
16TsSectionPat::TsSectionPat(const RegisterPmtCb& register_pmt_cb)
17    : register_pmt_cb_(register_pmt_cb),
18      version_number_(-1) {
19}
20
21TsSectionPat::~TsSectionPat() {
22}
23
24bool 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
116void TsSectionPat::ResetPsiSection() {
117  version_number_ = -1;
118}
119
120}  // namespace mp2t
121}  // namespace media
122
123