Incorrect endianness of TimeCode property in (Simple)Block object

[maurice-camp]

I'm trying to readout the timestamps for each datablock/frame in a matroska file. It seems however that the TimeCode property in the SimpleBlock object returns a value with little endianness while (according to https://matroska-org.github.io/libebml/specs.html) EBML integer datatypes are big-endian.

This leads to incorrect timestamps (when comparing to another tool like MKVToolNix):

MKVToolNix output:

If I manually revert endianness of the timecode file the values seem to match:

8448 -> 33
16896 -> 66
etc.

[StefH]

Hello @maurice-camp,

I think this is an issue related to NEbml, can you post your question there?

--> https://github.com/OlegZee/NEbml

[maurice-camp]

Hi @StefH

I looked into it a bit further and I dont think the issue is related to NEbml.
The Block.cs class uses the SpanReader class to retrieve the timecode from some binary data:

public virtual void Parse(Span<byte> span)
{
    var spanReader = new SpanReader(span);

    TrackNumber = spanReader.ReadVInt().Value;
    TimeCode = spanReader.ReadShort();
    Flags = spanReader.ReadByte();

The spanreader uses the MemoryMarshal.Read method for converting the byte array to a short:

[MethodImpl(MethodImplOptions.AggressiveInlining)]
public T Read<T>() where T : unmanaged
{
    var newSpan = _currentSpan.Slice(Position);
    var result = MemoryMarshal.Read<T>(newSpan);
    Position += Unsafe.SizeOf<T>();

    return result;
}

I think this method is architecture dependent when it comes to endianness causing the incorrect value.

[StefH]

#13

[StefH]

@maurice-camp

This will be fixed in new version which will be released shortly.