public static void unpackFrames(this Stream stream, ref Blob blob, ref LacedFrames laced)
{
eBlockFlags lacing = blob.lacing;
if (lacing == eBlockFlags.NoLacing)
{
// laced.frames?.Clear();
laced.lacing = eLacingResult.NoLacing;
return;
}
stream.Seek(blob.position, SeekOrigin.Begin);
int lacingHeader;
if (blob.length <= maxBuffer)
{
if (null != laced.buffer)
{
if (laced.buffer.Length < blob.length)
{
laced.buffer = new byte[blob.length];
}
}
else
{
laced.buffer = new byte[blob.length];
}
stream.read(laced.buffer.AsSpan().Slice(0, blob.length));
lacingHeader = laced.buffer[0];
laced.lacing = eLacingResult.Buffered;
}
else
{
lacingHeader = stream.ReadByte();
if (lacingHeader < 0)
{
throw new EndOfStreamException();
}
laced.lacing = eLacingResult.Large;
}
int lacedBlocksCount = lacingHeader + 1;
laced.initialize(lacedBlocksCount);
switch (lacing)
{
case eBlockFlags.FixedSize:
int cbPayload = blob.length - 1;
if (0 != cbPayload % lacedBlocksCount)
{
throw new ArgumentException($"Error in the MKV file, blob header specifies fixed size lacing with { lacedBlocksCount } laced frames, yet the block payload size { cbPayload } ain’t divisible");
}
int cbFrame = cbPayload / lacedBlocksCount;
for (int i = 0; i < lacedBlocksCount; i++)
{
laced.add(1 + cbFrame * i, cbFrame);
}
return;
case eBlockFlags.EBML:
if (laced.lacing == eLacingResult.Buffered)
{
unpackEbmlFromBuffer(lacedBlocksCount, laced.buffer.AsSpan().Slice(0, blob.length), ref laced);
}
else
{
unpackEbmlFromStream(lacedBlocksCount, stream, blob.length, ref laced);
}
break;
default:
throw new NotImplementedException($"{ lacing } lacing is not implemented");
}
}
static void unpackEbmlFromBuffer(int lacedBlocksCount, ReadOnlySpan <byte> buffer, ref LacedFrames laced)
{
// The count is stored in 1 byte, the absolute max.limit is 256, totally fine for the stack.
Span <int> sizes = stackalloc int[lacedBlocksCount];
int lacingHeaderBytes = 1; // The 1 byte is lacedBlocksCount we have already consumed from that buffer
int cb;
int prevSize = checked ((int)buffer.parseUint4(lacingHeaderBytes, out cb));
lacingHeaderBytes += cb;
sizes[0] = prevSize;
int combinedSize = prevSize;
for (int i = 1; i < lacedBlocksCount - 1; i++)
{
int difference = checked ((int)buffer.parseUint4(lacingHeaderBytes, out cb));
lacingHeaderBytes += cb;
prevSize += rangeShiftSignedInt(difference, cb);
sizes[i] = prevSize;
combinedSize += prevSize;
}
// The size of the last frame is deduced from the total size of the Block.
sizes[lacedBlocksCount - 1] = buffer.Length - lacingHeaderBytes - combinedSize;
int pos = lacingHeaderBytes;
for (int i = 0; i < lacedBlocksCount; i++)
{
laced.add(pos, sizes[i]);
pos += sizes[i];
}
}
static void unpackEbmlFromStream(int lacedBlocksCount, Stream stream, int blobSize, ref LacedFrames laced)
{
Span <int> sizes = stackalloc int[lacedBlocksCount];
int lacingHeaderBytes = 1; // The 1 byte is lacedBlocksCount we have already read
int cb;
int prevSize = checked ((int)stream.readUint4(out cb));
lacingHeaderBytes += cb;
sizes[0] = prevSize;
int combinedSize = prevSize;
for (int i = 1; i < lacedBlocksCount - 1; i++)
{
int difference = checked ((int)stream.readUint4(out cb));
lacingHeaderBytes += cb;
prevSize += rangeShiftSignedInt(difference, cb);
sizes[i] = prevSize;
combinedSize += prevSize;
}
// The size of the last frame is deduced from the total size of the Block.
sizes[lacedBlocksCount - 1] = blobSize - lacingHeaderBytes - combinedSize;
int pos = lacingHeaderBytes;
for (int i = 0; i < lacedBlocksCount; i++)
{
laced.add(pos, sizes[i]);
pos += sizes[i];
}
}