cluster_builder.cc

// Copyright 2014 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 <packager/media/formats/webm/cluster_builder.h>
 
#include <cstdint>
#include <cstring>
#include <memory>
#include <utility>
 
#include <absl/log/check.h>
 
#include <packager/media/formats/webm/webm_constants.h>
 
namespace shaka {
namespace media {
 
static const uint8_t kClusterHeader[] = {
    // clang-format off
    0x1F, 0x43, 0xB6, 0x75,                          // CLUSTER ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // cluster(size = 0)
    0xE7,                                            // Timecode ID
    0x88,                                            // timecode(size=8)
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // timecode value
    // clang-format on
};
 
static const uint8_t kSimpleBlockHeader[] = {
    // clang-format off
    0xA3,                                            // SimpleBlock ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // SimpleBlock(size = 0)
    // clang-format on
};
 
static const uint8_t kBlockGroupHeader[] = {
    // clang-format off
    0xA0,                                            // BlockGroup ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // BlockGroup(size = 0)
    0x9B,                                            // BlockDuration ID
    0x88,                                            // BlockDuration(size = 8)
    0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // duration
    0xA1,                                            // Block ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // Block(size = 0)
    // clang-format on
};
 
static const uint8_t kBlockGroupHeaderWithoutBlockDuration[] = {
    // clang-format off
    0xA0,                                            // BlockGroup ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // BlockGroup(size = 0)
    0xA1,                                            // Block ID
    0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,  // Block(size = 0)
    // clang-format on
};
 
static const uint8_t kBlockGroupReferenceBlock[] = {
    // clang-format off
    0xFB,        // ReferenceBlock ID
    0x81, 0x00,  // ReferenceBlock (size=1, value=0)
    // clang-format on
};
 
enum {
  kClusterSizeOffset = 4,
  kClusterTimecodeOffset = 14,
 
  kSimpleBlockSizeOffset = 1,
 
  kBlockGroupSizeOffset = 1,
  kBlockGroupWithoutBlockDurationBlockSizeOffset = 10,
  kBlockGroupDurationOffset = 11,
  kBlockGroupBlockSizeOffset = 20,
 
  kInitialBufferSize = 32768,
};
 
Cluster::Cluster(std::unique_ptr<uint8_t[]> data, int size)
    : data_(std::move(data)), size_(size) {}
Cluster::~Cluster() {}
 
ClusterBuilder::ClusterBuilder() {
  Reset();
}
ClusterBuilder::~ClusterBuilder() {}
 
void ClusterBuilder::SetClusterTimecode(int64_t cluster_timecode) {
  DCHECK_EQ(cluster_timecode_, -1);
 
  cluster_timecode_ = cluster_timecode;
 
  // Write the timecode into the header.
  uint8_t* buf = buffer_.get() + kClusterTimecodeOffset;
  for (int i = 7; i >= 0; --i) {
    buf[i] = cluster_timecode & 0xff;
    cluster_timecode >>= 8;
  }
}
 
void ClusterBuilder::AddSimpleBlock(int track_num,
                                    int64_t timecode,
                                    int flags,
                                    const uint8_t* data,
                                    int size) {
  int block_size = size + 4;
  int bytes_needed = sizeof(kSimpleBlockHeader) + block_size;
  if (bytes_needed > (buffer_size_ - bytes_used_))
    ExtendBuffer(bytes_needed);
 
  uint8_t* buf = buffer_.get() + bytes_used_;
  int block_offset = bytes_used_;
  memcpy(buf, kSimpleBlockHeader, sizeof(kSimpleBlockHeader));
  UpdateUInt64(block_offset + kSimpleBlockSizeOffset, block_size);
  buf += sizeof(kSimpleBlockHeader);
 
  WriteBlock(buf, track_num, timecode, flags, data, size);
 
  bytes_used_ += bytes_needed;
}
 
void ClusterBuilder::AddBlockGroup(int track_num,
                                   int64_t timecode,
                                   int duration,
                                   int flags,
                                   bool is_key_frame,
                                   const uint8_t* data,
                                   int size) {
  AddBlockGroupInternal(track_num, timecode, true, duration, flags,
                        is_key_frame, data, size);
}
 
void ClusterBuilder::AddBlockGroupWithoutBlockDuration(int track_num,
                                                       int64_t timecode,
                                                       int flags,
                                                       bool is_key_frame,
                                                       const uint8_t* data,
                                                       int size) {
  AddBlockGroupInternal(track_num, timecode, false, 0, flags, is_key_frame,
                        data, size);
}
 
void ClusterBuilder::AddBlockGroupInternal(int track_num,
                                           int64_t timecode,
                                           bool include_block_duration,
                                           int duration,
                                           int flags,
                                           bool is_key_frame,
                                           const uint8_t* data,
                                           int size) {
  int block_size = size + 4;
  int bytes_needed = block_size;
  if (include_block_duration) {
    bytes_needed += sizeof(kBlockGroupHeader);
  } else {
    bytes_needed += sizeof(kBlockGroupHeaderWithoutBlockDuration);
  }
  if (!is_key_frame) {
    bytes_needed += sizeof(kBlockGroupReferenceBlock);
  }
 
  int block_group_size = bytes_needed - 9;
 
  if (bytes_needed > (buffer_size_ - bytes_used_))
    ExtendBuffer(bytes_needed);
 
  uint8_t* buf = buffer_.get() + bytes_used_;
  int block_group_offset = bytes_used_;
  if (include_block_duration) {
    memcpy(buf, kBlockGroupHeader, sizeof(kBlockGroupHeader));
    UpdateUInt64(block_group_offset + kBlockGroupDurationOffset, duration);
    UpdateUInt64(block_group_offset + kBlockGroupBlockSizeOffset, block_size);
    buf += sizeof(kBlockGroupHeader);
  } else {
    memcpy(buf, kBlockGroupHeaderWithoutBlockDuration,
           sizeof(kBlockGroupHeaderWithoutBlockDuration));
    UpdateUInt64(
        block_group_offset + kBlockGroupWithoutBlockDurationBlockSizeOffset,
        block_size);
    buf += sizeof(kBlockGroupHeaderWithoutBlockDuration);
  }
 
  UpdateUInt64(block_group_offset + kBlockGroupSizeOffset, block_group_size);
 
  // Make sure the 4 most-significant bits are 0.
  // http://www.matroska.org/technical/specs/index.html#block_structure
  flags &= 0x0f;
 
  WriteBlock(buf, track_num, timecode, flags, data, size);
  buf += size + 4;
 
  if (!is_key_frame)
    memcpy(buf, kBlockGroupReferenceBlock, sizeof(kBlockGroupReferenceBlock));
  bytes_used_ += bytes_needed;
}
 
void ClusterBuilder::WriteBlock(uint8_t* buf,
                                int track_num,
                                int64_t timecode,
                                int flags,
                                const uint8_t* data,
                                int size) {
  DCHECK_GE(track_num, 0);
  DCHECK_LE(track_num, 126);
  DCHECK_GE(flags, 0);
  DCHECK_LE(flags, 0xff);
  DCHECK(data);
  DCHECK_GT(size, 0);
  DCHECK_NE(cluster_timecode_, -1);
 
  int64_t timecode_delta = timecode - cluster_timecode_;
  DCHECK_GE(timecode_delta, -32768);
  DCHECK_LE(timecode_delta, 32767);
 
  buf[0] = 0x80 | (track_num & 0x7F);
  buf[1] = (timecode_delta >> 8) & 0xff;
  buf[2] = timecode_delta & 0xff;
  buf[3] = flags & 0xff;
  memcpy(buf + 4, data, size);
}
 
std::unique_ptr<Cluster> ClusterBuilder::Finish() {
  DCHECK_NE(cluster_timecode_, -1);
 
  UpdateUInt64(kClusterSizeOffset, bytes_used_ - (kClusterSizeOffset + 8));
 
  std::unique_ptr<Cluster> ret(new Cluster(std::move(buffer_), bytes_used_));
  Reset();
  return ret;
}
 
std::unique_ptr<Cluster> ClusterBuilder::FinishWithUnknownSize() {
  DCHECK_NE(cluster_timecode_, -1);
 
  UpdateUInt64(kClusterSizeOffset, kWebMUnknownSize);
 
  std::unique_ptr<Cluster> ret(new Cluster(std::move(buffer_), bytes_used_));
  Reset();
  return ret;
}
 
void ClusterBuilder::Reset() {
  buffer_size_ = kInitialBufferSize;
  buffer_.reset(new uint8_t[buffer_size_]);
  memcpy(buffer_.get(), kClusterHeader, sizeof(kClusterHeader));
  bytes_used_ = sizeof(kClusterHeader);
  cluster_timecode_ = -1;
}
 
void ClusterBuilder::ExtendBuffer(int bytes_needed) {
  int new_buffer_size = 2 * buffer_size_;
 
  while ((new_buffer_size - bytes_used_) < bytes_needed)
    new_buffer_size *= 2;
 
  std::unique_ptr<uint8_t[]> new_buffer(new uint8_t[new_buffer_size]);
 
  memcpy(new_buffer.get(), buffer_.get(), bytes_used_);
  buffer_.reset(new_buffer.release());
  buffer_size_ = new_buffer_size;
}
 
void ClusterBuilder::UpdateUInt64(int offset, int64_t value) {
  DCHECK_LE(offset + 7, buffer_size_);
  uint8_t* buf = buffer_.get() + offset;
 
  // Fill the last 7 bytes of size field in big-endian order.
  for (int i = 7; i > 0; i--) {
    buf[i] = value & 0xff;
    value >>= 8;
  }
}
 
}  // namespace media
}  // namespace shaka