Mpeg2 TS stream parser for media source.

media/mp2t/ts_section_pat.cc

+// Copyright (c) 2013 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 "media/mp2t/ts_section_pat.h"
+
+#include <vector>
+
+#include "base/logging.h"
+#include "media/base/bit_reader.h"
+#include "media/mp2t/mp2t_common.h"
+
+namespace media {
+namespace mp2t {
+
+TsSectionPat::TsSectionPat(RegisterPmtCb register_pmt_cb)
+    : register_pmt_cb_(register_pmt_cb),
+      version_number_(-1) {
+}
+
+TsSectionPat::~TsSectionPat() {
+}
+
+bool TsSectionPat::ParsePsiSection(BitReader* bit_reader) {
+  // Read the fixed section length.
+  int table_id;
+  bool section_syntax_indicator;
+  bool dummy_zero;
+  int reserved;
+  int section_length;
+  int transport_stream_id;
+  int version_number;
+  bool 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));
+  RCHECK(section_length >= 5);
+  RCHECK(bit_reader->ReadBits(16, &transport_stream_id));
+  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));
+  section_length -= 5;
+
+  // Perform a few verifications:
+  // - Table ID should be 0 for a PAT.
+  // - section_syntax_indicator should be one.
+  // - section length should not exceed 1021
+  RCHECK(table_id == 0x0);
+  RCHECK(section_syntax_indicator);
+  RCHECK(!dummy_zero);
+  RCHECK(section_length <= 1021);

[acolwell GONE FROM CHROMIUM, 2013/09/16 06:19:30]

s/1021/1016 to compensate for the -= 5 above?

[damienv1, 2013/09/17 02:58:22]

Good catch. I moved all the RCHECK together in a previous patch set and I just
forgot section_length was modified in between. Thanks.

+
+  // Both the program table and the CRC have a size multiple of 4.
+  // Note for pmt_pid_count: minus 4 to account for the CRC.
+  RCHECK((section_length & 0x3) == 0);

[acolwell GONE FROM CHROMIUM, 2013/09/16 06:19:30]

nit: s/& 0x3/% 4/ just to make it easier to see that this matches what the
comment says?

[damienv1, 2013/09/17 02:58:22]

Done.

+  int pmt_pid_count = (section_length - 4) / 4;
+
+  // Read the variable length section: program table & crc.
+  std::vector<int> program_number_array(pmt_pid_count);
+  std::vector<int> pmt_pid_array(pmt_pid_count);
+  for (int k = 0; k < pmt_pid_count; k++) {
+    int reserved;
+    RCHECK(bit_reader->ReadBits(16, &program_number_array[k]));
+    RCHECK(bit_reader->ReadBits(3, &reserved));
+    RCHECK(bit_reader->ReadBits(13, &pmt_pid_array[k]));
+  }
+  int crc32;
+  RCHECK(bit_reader->ReadBits(32, &crc32));
+
+  // Just ignore the PAT if not applicable yet.
+  if (!current_next_indicator) {
+    DVLOG(1) << "Not supported: received a PAT not applicable yet";
+    return true;
+  }
+
+  // Ignore the program table if it hasn't changed.
+  if (version_number == version_number_)
+    return true;
+
+  // Both the MSE and the HLS spec specifies that TS streams should convey
+  // exactly one program.
+  if (pmt_pid_count > 1)
+    return false;

[acolwell GONE FROM CHROMIUM, 2013/09/16 06:19:30]

nit: A DVLOG saying multiple programs were detected would probably be a good
idea.

[damienv1, 2013/09/17 02:58:22]

Done.

+
+  // Can now register the PMT.
+  int expected_version_number = version_number;
+  if (version_number_ >= 0)
+    expected_version_number = (version_number_ + 1) % 32;
+  DVLOG_IF(1, version_number != expected_version_number)
+      << "Unexpected version number: "
+      << version_number << " vs " << version_number_;
+  for (int k = 0; k < pmt_pid_count; k++) {
+    if (program_number_array[k] != 0) {
+      // Program numbers different from 0 correspond to PMT.
+      register_pmt_cb_.Run(program_number_array[k], pmt_pid_array[k]);
+      // Even if there are multiple programs, only one can be supported now.
+      // HLS: "Transport Stream segments MUST contain a single MPEG-2 Program."
+      break;
+    }
+  }
+  version_number_ = version_number;
+
+  return true;
+}
+
+void TsSectionPat::ResetPsiSection() {
+  version_number_ = -1;
+}
+
+}  // namespace mp2t
+}  // namespace media
+