Mpeg2 TS stream parser for media source.

media/mpeg2/mpeg2ts_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/mpeg2/mpeg2ts_pat.h"
+
+#include "base/logging.h"
+#include "media/base/bit_reader.h"
+#include "media/mpeg2/mpeg2ts_common.h"
+
+namespace media {
+namespace mpeg2ts {
+
+Mpeg2TsPatParser::Mpeg2TsPatParser(RegisterPmtCb register_pmt_cb)
+    : register_pmt_cb_(register_pmt_cb),
+      version_number_(-1) {
+}
+
+Mpeg2TsPatParser::~Mpeg2TsPatParser() {
+}
+
+bool Mpeg2TsPatParser::ParsePsiSection(BitReader* bit_reader) {
+  // Read the fixed section length.
+  int remaining_size = bit_reader->bits_available() / 8;
+  if (remaining_size < 8) {
+    LOG(WARNING) << "remaining_size=" << remaining_size;

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

nit: DVLOG

[damienv1, 2013/09/09 23:29:45]

Done.

+    return false;
+  }
+  int table_id;
+  DCHECK(bit_reader->ReadBits(8, &table_id));
+  bool section_syntax_indicator;

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

nit: put all declarations together to make this easier to read.

[damienv1, 2013/09/09 23:29:45]

Done.

+  DCHECK(bit_reader->ReadBits(1, &section_syntax_indicator));

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

These should be RCHECK otherwise these won't run in release builds.

[damienv1, 2013/09/09 23:29:45]

Running this is safe in release builds: I just check before that I had at least
8*8 = 64 bits available. Pros: check is done only once instead of using RCHECK
for every ReadBits call.

[acolwell GONE FROM CHROMIUM, 2013/09/12 19:59:50]

But none of the code in a DCHECK runs in a release build. All of the variables
will have random values because ReadBits() won't actually be called. It is not
safe to assume that the expression in a DCHECK will actually be evaluated in
prelease builds.

Please just use RCHECK in all the places I mentioned it should be used instead
of DCHECK. We can optimize this code later if the checks become a significant
perf problem.

[damienv1, 2013/09/12 20:53:51]

OK, my mistake. If we had to use DCHECK, it would be:
bool status = ReadBits(...);
DCHECK(status);

=> Will replace by RCHECK in all the places.

+  bool dummy_zero;
+  DCHECK(bit_reader->ReadBits(1, &dummy_zero));
+  int reserved;
+  DCHECK(bit_reader->ReadBits(2, &reserved));
+  int section_length;
+  DCHECK(bit_reader->ReadBits(12, &section_length));
+  int transport_stream_id;
+  DCHECK(bit_reader->ReadBits(16, &transport_stream_id));
+  DCHECK(bit_reader->ReadBits(2, &reserved));
+  int version_number;
+  DCHECK(bit_reader->ReadBits(5, &version_number));
+  bool current_next_indicator;
+  DCHECK(bit_reader->ReadBits(1, &current_next_indicator));
+  int section_number;
+  DCHECK(bit_reader->ReadBits(8, &section_number));
+  int last_section_number;
+  DCHECK(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);
+
+  // Make sure there are enough bits for the variable section.
+  remaining_size = bit_reader->bits_available() / 8;
+  if (remaining_size < section_length) {
+    LOG(WARNING) << "remaining_size=" << remaining_size;

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

DVLOG here and all cases below.

[damienv1, 2013/09/09 23:29:45]

Done.

+    return false;
+  }
+  LOG_IF(WARNING, remaining_size > section_length)
+      << "Trailing bytes after the PAT: nbytes="
+      << (remaining_size - section_length);
+
+  // 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.
+  if ((section_length & 0x3) != 0) {
+    LOG(WARNING) << "PAT table size should be a multiple of 4";
+    return false;
+  }
+  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++) {
+    DCHECK(bit_reader->ReadBits(16, &program_number_array[k]));

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

RCHECK here and below

[damienv1, 2013/09/09 23:29:45]

By design, we should not run out of bits in this section, that's why I use a
DCHECK.
pmt_pid_count is based on the section_length which itself has been verified to
be equal to or less than the remaining number of bits.

+    int reserved;
+    DCHECK(bit_reader->ReadBits(3, &reserved));

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

RCHECK reserved value

[damienv1, 2013/09/09 23:29:45]

Ditto.

+    DCHECK(bit_reader->ReadBits(13, &pmt_pid_array[k]));
+  }
+  int crc32;
+  DCHECK(bit_reader->ReadBits(32, &crc32));
+
+  // Just ignore the PAT if not applicable yet.
+  if (!current_next_indicator) {
+    LOG(WARNING) << "Not supported: received a PAT not applicable yet";
+    return true;
+  }
+
+  // Ignore the program table if it hasn't changed.
+  if (version_number == version_number_) {

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

nit: remove {}

[damienv1, 2013/09/09 23:29:45]

Done.

+    return true;
+  }
+
+  // Can now register the PMT.
+  int expected_version_number = version_number;
+  if (version_number_ >= 0) {
+    expected_version_number = (version_number_ + 1) % 32;
+  }
+  LOG_IF(WARNING, 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."

[acolwell GONE FROM CHROMIUM, 2013/09/05 18:29:10]

If this code is detecting multiple programs here, it should return false to
trigger an error.

[damienv1, 2013/09/09 23:29:45]

Done.

+      break;
+    }
+  }
+  version_number_ = version_number;
+
+  return true;
+}
+
+}  // namespace mpeg2ts
+}  // namespace media