[Matroska-devel] EBML specification component for review - Element Data Size

Jerome Martinez jerome at mediaarea.net
Sat May 2 18:23:16 CEST 2015


Le 02/05/2015 18:08, Steve Lhomme a écrit :
>
>
> As said in one of the proposed text, unknown size elements MUST be 
> master/list elements. They cannot be binary blobs or numbers. I don't 
> think it's written anywhere, but it should. Although as in a lot of 
> case with these unwritten rules, they are pretty obvious.

In a specification, nothing can be "pretty obvious", all must be written.
If it is not written, let's add it.

that said, it is not so true for binary blobs: we can imagine we start 
to write a frame without knowing the size of the frame (because we have 
only its first slice at the moment of writing, low latency mode without 
being "real time") and we'll write the size of the frame only when we 
get the last slice.
FYI, this is used in MXF format ("incomplete" mode) and the unknown size 
of the blob is present in the file if the muxer crashed (most player can 
play the file despite this unknown element size, size is considered to 
be up to the end of the file). So I would not forbid unknown size 
element for binary blobs.


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