Mpeg2 TS stream parser for media source.

media/mp2t/ts_packet.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_packet.h"
+
+#include "base/memory/scoped_ptr.h"
+#include "media/base/bit_reader.h"
+#include "media/mp2t/mp2t_common.h"
+
+namespace media {
+namespace mp2t {
+
+static const uint8 kTsHeaderSyncword = 0x47;
+
+// static
+int TsPacket::Sync(const uint8* buf, int size) {
+  int k = 0;
+  for (; k < size; k++) {
+    // Verify that we have 4 syncwords in a row when possible,
+    // this should improve synchronization robustness.
+    // TODO(damienv): Consider the case where there is garbage
+    // between TS packets.
+    bool is_header = true;
+    for (int i = 0; i < 4; i++) {
+      int idx = k + i * kPacketSize;
+      if (idx >= size)
+        break;
+      if (buf[idx] != kTsHeaderSyncword) {
+        DVLOG(LOG_LEVEL_TS)
+            << "ByteSync" << idx << ": "
+            << std::hex << static_cast<int>(buf[idx]) << std::dec;
+        is_header = false;
+        break;
+      }
+    }
+    if (is_header) {

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

nit: remove {}

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

Done.

+      break;
+    }
+  }
+
+  LOG_IF(WARNING, k != 0) << "SYNC: nbytes_skipped=" << k;

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

nit: convert to DVLOG

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

Done.

+  return k;
+}
+
+// static
+TsPacket* TsPacket::Parse(const uint8* buf, int size) {
+  if (size < kPacketSize) {
+    LOG(WARNING) << "Buffer does not hold one full TS packet:"

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

nit: convert to DVLOG

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

Done.

+                 << " buffer_size=" << size;
+    return NULL;
+  }
+
+  DCHECK_EQ(buf[0], kTsHeaderSyncword);
+  if (buf[0] != kTsHeaderSyncword) {
+    DVLOG(1) << "Not on a TS syncword:"
+             << " buf[0]="
+             << std::hex << static_cast<int>(buf[0]) << std::dec;
+    return NULL;
+  }
+
+  scoped_ptr<TsPacket> ts_packet(new TsPacket());
+  BitReader bit_reader(buf, kPacketSize);
+
+  bool status = ts_packet->ParseHeader(&bit_reader);
+  if (!status) {
+    DVLOG(1) << "Parsing header failed";
+    return NULL;
+  }
+  ts_packet->payload_ = buf + (kPacketSize - ts_packet->payload_size_);

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

nit: These seems out of place. How about just passing buf & size to
ParseHeader() so you don't need to do this?

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

Done.

+
+  return ts_packet.release();
+}
+
+TsPacket::TsPacket() {
+}
+
+TsPacket::~TsPacket() {
+}
+
+bool TsPacket::ParseHeader(BitReader* bit_reader) {
+  payload_size_ = kPacketSize;
+
+  // Read the TS header: 4 bytes.
+  int syncword;
+  bool transport_error_indicator;
+  bool transport_priority;
+  int transport_scrambling_control;
+  int adaptation_field_control;
+  RCHECK(bit_reader->ReadBits(8, &syncword));
+  RCHECK(bit_reader->ReadBits(1, &transport_error_indicator));
+  RCHECK(bit_reader->ReadBits(1, &payload_unit_start_indicator_));
+  RCHECK(bit_reader->ReadBits(1, &transport_priority));
+  RCHECK(bit_reader->ReadBits(13, &pid_));
+  RCHECK(bit_reader->ReadBits(2, &transport_scrambling_control));
+  RCHECK(bit_reader->ReadBits(2, &adaptation_field_control));
+  RCHECK(bit_reader->ReadBits(4, &continuity_counter_));
+  payload_size_ -= 4;
+
+  // Default values when no adaptation field.
+  discontinuity_indicator_ = false;
+  random_access_indicator_ = false;
+
+  // Done since no adaptation field.
+  if ((adaptation_field_control & 0x2) == 0)
+    return true;
+
+  // Read the adaptation field if needed.
+  int adaptation_field_length;
+  RCHECK(bit_reader->ReadBits(8, &adaptation_field_length));
+  DVLOG(LOG_LEVEL_TS) << "adaptation_field_length=" << adaptation_field_length;
+  payload_size_ -= 1;
+  if ((adaptation_field_control & 0x1) == 0 &&
+       adaptation_field_length != 183) {
+    DVLOG(1) << "adaptation_field_length=" << adaptation_field_length;
+    return false;
+  }
+  if ((adaptation_field_control & 0x1) == 1 &&
+       adaptation_field_length > 182) {
+    DVLOG(1) << "adaptation_field_length=" << adaptation_field_length;
+    // This is not allowed by the spec.
+    // However, some badly encoded streams are using
+    // adaptation_field_length = 183
+    // return false;

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

nit: We should not encourage this behavior. I think we should return false here.
Unless the Apple encoder does this, I think we should reject these streams.

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

Done.

+  }
+
+  // adaptation_field_length = '0' is used to insert a single stuffing byte
+  // in the adaptation field of a transport stream packet.
+  if (adaptation_field_length == 0)
+    return true;
+
+  bool status = ParseAdaptationField(bit_reader, adaptation_field_length);
+  payload_size_ -= adaptation_field_length;
+  return status;
+}
+
+bool TsPacket::ParseAdaptationField(BitReader* bit_reader,
+                                    int adaptation_field_length) {
+  DCHECK_GT(adaptation_field_length, 0);
+
+  bool elementary_stream_priority_indicator;
+  bool pcr_flag;
+  bool opcr_flag;
+  bool splicing_point_flag;
+  bool transport_private_data_flag;
+  bool adaptation_field_extension_flag;
+  RCHECK(bit_reader->ReadBits(1, &discontinuity_indicator_));
+  RCHECK(bit_reader->ReadBits(1, &random_access_indicator_));
+  RCHECK(bit_reader->ReadBits(1, &elementary_stream_priority_indicator));
+  RCHECK(bit_reader->ReadBits(1, &pcr_flag));
+  RCHECK(bit_reader->ReadBits(1, &opcr_flag));
+  RCHECK(bit_reader->ReadBits(1, &splicing_point_flag));
+  RCHECK(bit_reader->ReadBits(1, &transport_private_data_flag));
+  RCHECK(bit_reader->ReadBits(1, &adaptation_field_extension_flag));
+  adaptation_field_length -= 1;

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

nit: You shouldn't need to do all these length updates. Just capture
bits_available() at the top and then check it again at the bottom. I think that
would be less error prone.

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

Done.

+
+  if (pcr_flag) {
+    RCHECK(adaptation_field_length >= 6);

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

These types of checks shouldn't be needed since you are using RCHECKs below.

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

Done.

+    int64 program_clock_reference_base;
+    int reserved;
+    int program_clock_reference_extension;
+    RCHECK(bit_reader->ReadBits(33, &program_clock_reference_base));
+    RCHECK(bit_reader->ReadBits(6, &reserved));
+    RCHECK(bit_reader->ReadBits(9, &program_clock_reference_extension));
+    adaptation_field_length -= 6;
+  }
+
+  if (opcr_flag) {
+    RCHECK(adaptation_field_length >= 6);
+    int64 original_program_clock_reference_base;
+    int reserved;
+    int original_program_clock_reference_extension;
+    RCHECK(bit_reader->ReadBits(33, &original_program_clock_reference_base));
+    RCHECK(bit_reader->ReadBits(6, &reserved));
+    RCHECK(
+        bit_reader->ReadBits(9, &original_program_clock_reference_extension));
+    adaptation_field_length -= 6;
+  }
+
+  if (splicing_point_flag) {
+    RCHECK(adaptation_field_length >= 1);
+    int splice_countdown;
+    RCHECK(bit_reader->ReadBits(8, &splice_countdown));
+    adaptation_field_length -= 1;
+  }
+
+  if (transport_private_data_flag) {
+    RCHECK(adaptation_field_length >= 1);
+    int transport_private_data_length;
+    RCHECK(bit_reader->ReadBits(8, &transport_private_data_length));
+    adaptation_field_length -= 1;
+
+    RCHECK(adaptation_field_length >= transport_private_data_length);
+    for (int k = 0; k < transport_private_data_length; k++) {
+      int private_data_byte;
+      RCHECK(bit_reader->ReadBits(8, &private_data_byte));

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

nit: You should be able to use RCHECK(bit_reader->SkipBits(8 *
transport_private_data_length)) instead of a loop here.

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

Done.

+    }
+    adaptation_field_length -= transport_private_data_length;
+  }
+
+  if (adaptation_field_extension_flag) {
+    RCHECK(adaptation_field_length >= 1);
+    int adaptation_field_extension_length;
+    RCHECK(bit_reader->ReadBits(8, &adaptation_field_extension_length));
+    adaptation_field_length -= 1;
+
+    RCHECK(adaptation_field_length >= adaptation_field_extension_length);
+    for (int k = 0; k < adaptation_field_extension_length; k++) {
+      int dummy_byte;
+      RCHECK(bit_reader->ReadBits(8, &dummy_byte));

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

ditto re: SkipBits()

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

Done.

+    }
+    adaptation_field_length -= adaptation_field_extension_length;
+  }
+
+  for (int k = 0; k < adaptation_field_length; k++) {
+    int stuffing_byte;
+    RCHECK(bit_reader->ReadBits(8, &stuffing_byte));
+    RCHECK(stuffing_byte == 0xff);
+  }
+
+  DVLOG(LOG_LEVEL_TS) << "random_access_indicator=" << random_access_indicator_;
+  return true;
+}
+
+const uint8* TsPacket::GetPayload() const {
+  return payload_;
+}
+
+int TsPacket::GetPayloadSize() const {
+  return payload_size_;
+}
+
+}  // namespace mp2t
+}  // namespace media
+