uint64 EbmlElementSize(uint64 type, const char* value) {
if (!value)
return 0;
// Size of EBML ID
uint64 ebml_size = GetUIntSize(type);
// Datasize
ebml_size += strlen(value);
// Size of Datasize
ebml_size++;
return ebml_size;
}
uint64 EbmlElementSize(uint64 type, const uint8* value, uint64 size) {
if (!value)
return 0;
// Size of EBML ID
uint64 ebml_size = GetUIntSize(type);
// Datasize
ebml_size += size;
// Size of Datasize
ebml_size += GetCodedUIntSize(size);
return ebml_size;
}
bool WriteEbmlElement(IMkvWriter* writer, uint64 type, uint64 value) {
if (!writer)
return false;
if (WriteID(writer, type))
return false;
const uint64 size = GetUIntSize(value);
if (WriteUInt(writer, size))
return false;
if (SerializeInt(writer, value, static_cast<int32>(size)))
return false;
return true;
}
// We must write the metadata (key)frame as a BlockGroup element,
// because we need to specify a duration for the frame. The
// BlockGroup element comprises the frame itself and its duration,
// and is laid out as follows:
//
// BlockGroup tag
// BlockGroup size
// Block tag
// Block size
// (the frame is the block payload)
// Duration tag
// Duration size
// (duration payload)
//
uint64 WriteMetadataBlock(IMkvWriter* writer,
const uint8* data,
uint64 length,
uint64 track_number,
int64 timecode,
uint64 duration) {
// We don't backtrack when writing to the stream, so we must
// pre-compute the BlockGroup size, by summing the sizes of each
// sub-element (the block and the duration).
// We use a single byte for the track number of the block, which
// means the block header is exactly 4 bytes.
// TODO(matthewjheaney): use EbmlMasterElementSize and WriteEbmlMasterElement
const uint64 block_payload_size = 4 + length;
const int32 block_size = GetCodedUIntSize(block_payload_size);
const uint64 block_elem_size = 1 + block_size + block_payload_size;
const int32 duration_payload_size = GetUIntSize(duration);
const int32 duration_size = GetCodedUIntSize(duration_payload_size);
const uint64 duration_elem_size = 1 + duration_size + duration_payload_size;
const uint64 blockg_payload_size = block_elem_size + duration_elem_size;
const int32 blockg_size = GetCodedUIntSize(blockg_payload_size);
const uint64 blockg_elem_size = 1 + blockg_size + blockg_payload_size;
if (WriteID(writer, kMkvBlockGroup)) // 1-byte ID size
return 0;
if (WriteUInt(writer, blockg_payload_size))
return 0;
// Write Block element
if (WriteID(writer, kMkvBlock)) // 1-byte ID size
return 0;
if (WriteUInt(writer, block_payload_size))
return 0;
// Byte 1 of 4
if (WriteUInt(writer, track_number))
return 0;
// Bytes 2 & 3 of 4
if (SerializeInt(writer, timecode, 2))
return 0;
// Byte 4 of 4
const uint64 flags = 0;
if (SerializeInt(writer, flags, 1))
return 0;
// Now write the actual frame (of metadata)
if (writer->Write(data, static_cast<uint32>(length)))
return 0;
// Write Duration element
if (WriteID(writer, kMkvBlockDuration)) // 1-byte ID size
return 0;
if (WriteUInt(writer, duration_payload_size))
return 0;
if (SerializeInt(writer, duration, duration_payload_size))
return 0;
// Note that we don't write a reference time as part of the block
// group; no reference time(s) indicates that this block is a
// keyframe. (Unlike the case for a SimpleBlock element, the header
// bits of the Block sub-element of a BlockGroup element do not
// indicate keyframe status. The keyframe status is inferred from
// the absence of reference time sub-elements.)
return blockg_elem_size;
}
int32 GetIntSize(int64 value) {
// Doubling the requested value ensures positive values with their high bit
// set are written with 0-padding to avoid flipping the signedness.
const uint64 v = (value < 0) ? value ^ -1LL : value;
return GetUIntSize(2 * v);
}
