ts_writer.cc

// Copyright 2016 Google LLC. All rights reserved.
//
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file or at
// https://developers.google.com/open-source/licenses/bsd
 
#include <packager/media/formats/mp2t/ts_writer.h>
 
#include <algorithm>
#include <cstddef>
#include <cstdint>
#include <iterator>
#include <memory>
#include <utility>
 
#include <absl/log/log.h>
 
#include <packager/media/base/buffer_writer.h>
#include <packager/media/formats/mp2t/pes_packet.h>
#include <packager/media/formats/mp2t/program_map_table_writer.h>
#include <packager/media/formats/mp2t/ts_packet_writer_util.h>
 
namespace shaka {
namespace media {
namespace mp2t {
 
namespace {
 
// For all the pointer fields in the following PAT and PMTs, they are not really
// part of PAT or PMT but it's there so that TsPacket can point to a memory
// location that starts from pointer field.
const uint8_t kProgramAssociationTableId = 0x00;
 
// This PAT can be used for both encrypted and clear.
const uint8_t kPat[] = {
    // clang-format off
    0x00,  // pointer field
    kProgramAssociationTableId,
    0xB0,        // The last 2 '00' assumes that this PAT is not very long.
    0x0D,        // Length of the rest of this array.
    0x00, 0x00,  // Transport stream ID is 0.
    0xC1,        // version number 0, current next indicator 1.
    0x00,        // section number
    0x00,        // last section number
    // program number -> PMT PID mapping.
    0x00, 0x01,  // program number is 1.
    0xE0,        // first 3 bits is reserved.
    ProgramMapTableWriter::kPmtPid,
    // CRC32.
    0xF9, 0x62, 0xF5, 0x8B,
    // clang-format on
};
 
const bool kHasPcr = true;
const bool kPayloadUnitStartIndicator = true;
 
// This is the size of the first few fields in a TS packet, i.e. TS packet size
// without adaptation field or the payload.
const int kTsPacketHeaderSize = 4;
const int kTsPacketSize = 188;
const int kTsPacketMaximumPayloadSize = kTsPacketSize - kTsPacketHeaderSize;
 
const size_t kMaxPesPacketLengthValue = 0xFFFF;
 
void WritePatToBuffer(const uint8_t* pat,
                      int pat_size,
                      ContinuityCounter* continuity_counter,
                      BufferWriter* writer) {
  const int kPatPid = 0;
  WritePayloadToBufferWriter(pat, pat_size, kPayloadUnitStartIndicator, kPatPid,
                             !kHasPcr, 0, continuity_counter, writer);
}
 
// The only difference between writing PTS or DTS is the leading bits.
void WritePtsOrDts(uint8_t leading_bits,
                   uint64_t pts_or_dts,
                   BufferWriter* writer) {
  // First byte has 3 MSB of PTS.
  uint8_t first_byte =
      leading_bits << 4 | (((pts_or_dts >> 30) & 0x07) << 1) | 1;
  // Second byte has the next 8 bits of pts.
  uint8_t second_byte = (pts_or_dts >> 22) & 0xFF;
  // Third byte has the next 7 bits of pts followed by a marker bit.
  uint8_t third_byte = (((pts_or_dts >> 15) & 0x7F) << 1) | 1;
  // Fourth byte has the next 8 bits of pts.
  uint8_t fourth_byte = ((pts_or_dts >> 7) & 0xFF);
  // Fifth byte has the last 7 bits of pts followed by a marker bit.
  uint8_t fifth_byte = ((pts_or_dts & 0x7F) << 1) | 1;
  writer->AppendInt(first_byte);
  writer->AppendInt(second_byte);
  writer->AppendInt(third_byte);
  writer->AppendInt(fourth_byte);
  writer->AppendInt(fifth_byte);
}
 
bool WritePesToBuffer(const PesPacket& pes,
                      ContinuityCounter* continuity_counter,
                      BufferWriter* current_buffer) {
  // The size of the length field.
  const int kAdaptationFieldLengthSize = 1;
  // The size of the flags field.
  const int kAdaptationFieldHeaderSize = 1;
  const int kPcrFieldSize = 6;
  const int kTsPacketMaxPayloadWithPcr =
      kTsPacketMaximumPayloadSize - kAdaptationFieldLengthSize -
      kAdaptationFieldHeaderSize - kPcrFieldSize;
  const uint64_t pcr_base = pes.has_dts() ? pes.dts() : pes.pts();
  const int pid = ProgramMapTableWriter::kElementaryPid;
 
  // This writer will hold part of PES packet after PES_packet_length field.
  BufferWriter pes_header_writer;
  // The first bit must be '10' for PES with video or audio stream id. The other
  // flags (bits) don't matter so they are 0.
  pes_header_writer.AppendInt(static_cast<uint8_t>(0x80));
  pes_header_writer.AppendInt(
      static_cast<uint8_t>(static_cast<int>(pes.has_pts()) << 7 |
                           static_cast<int>(pes.has_dts()) << 6
                           // Other fields are all 0.
                           ));
  uint8_t pes_header_data_length = 0;
  if (pes.has_pts())
    pes_header_data_length += 5;
  if (pes.has_dts())
    pes_header_data_length += 5;
  pes_header_writer.AppendInt(pes_header_data_length);
 
  if (pes.has_pts() && pes.has_dts()) {
    WritePtsOrDts(0x03, pes.pts(), &pes_header_writer);
    WritePtsOrDts(0x01, pes.dts(), &pes_header_writer);
  } else if (pes.has_pts()) {
    WritePtsOrDts(0x02, pes.pts(), &pes_header_writer);
  }
 
  // Put the first TS packet's payload into a buffer. This contains the PES
  // packet's header.
  BufferWriter first_ts_packet_buffer(kTsPacketSize);
  first_ts_packet_buffer.AppendNBytes(static_cast<uint64_t>(0x000001), 3);
  first_ts_packet_buffer.AppendInt(pes.stream_id());
  const size_t pes_packet_length = pes.data().size() + pes_header_writer.Size();
  first_ts_packet_buffer.AppendInt(static_cast<uint16_t>(
      pes_packet_length > kMaxPesPacketLengthValue ? 0 : pes_packet_length));
  first_ts_packet_buffer.AppendBuffer(pes_header_writer);
 
  const size_t available_payload =
      kTsPacketMaxPayloadWithPcr - first_ts_packet_buffer.Size();
  const size_t bytes_consumed = std::min(pes.data().size(), available_payload);
  first_ts_packet_buffer.AppendArray(pes.data().data(), bytes_consumed);
 
  BufferWriter output_writer;
  WritePayloadToBufferWriter(first_ts_packet_buffer.Buffer(),
                             first_ts_packet_buffer.Size(),
                             kPayloadUnitStartIndicator, pid, kHasPcr, pcr_base,
                             continuity_counter, &output_writer);
 
  const size_t remaining_pes_data_size = pes.data().size() - bytes_consumed;
  if (remaining_pes_data_size > 0) {
    WritePayloadToBufferWriter(pes.data().data() + bytes_consumed,
                               remaining_pes_data_size,
                               !kPayloadUnitStartIndicator, pid, !kHasPcr, 0,
                               continuity_counter, &output_writer);
  }
 
  current_buffer->AppendBuffer(output_writer);
  return true;
}
 
}  // namespace
 
TsWriter::TsWriter(std::unique_ptr<ProgramMapTableWriter> pmt_writer)
    : pmt_writer_(std::move(pmt_writer)) {}
 
TsWriter::~TsWriter() {}
 
bool TsWriter::NewSegment(BufferWriter* buffer) {
  BufferWriter psi;
  WritePatToBuffer(kPat, std::size(kPat), &pat_continuity_counter_, &psi);
  if (encrypted_) {
    if (!pmt_writer_->EncryptedSegmentPmt(&psi)) {
      return false;
    }
  } else {
    if (!pmt_writer_->ClearSegmentPmt(&psi)) {
      return false;
    }
  }
  buffer->AppendBuffer(psi);
 
  return true;
}
 
void TsWriter::SignalEncrypted() {
  encrypted_ = true;
}
 
bool TsWriter::AddPesPacket(std::unique_ptr<PesPacket> pes_packet,
                            BufferWriter* buffer) {
  if (!WritePesToBuffer(*pes_packet, &elementary_stream_continuity_counter_,
                        buffer)) {
    LOG(ERROR) << "Failed to write pes to buffer.";
    return false;
  }
 
  // No need to keep pes_packet around so not passing it anywhere.
  return true;
}
 
}  // namespace mp2t
}  // namespace media
}  // namespace shaka