[Matroska-devel] Several (minor) issues or underspecified areas in the MKV spec

Michael Bradshaw mjbshaw at google.com
Fri Nov 20 20:08:39 CET 2015


On Fri, Nov 20, 2015 at 10:56 AM, Moritz Bunkus <moritz at bunkus.org> wrote:

> Hey,
>
> > How should mandatory master elements be handled if they are not
> > present in the bitstream?
>
> The Matroska spec notes[1] deal with this explicitly. Quote:
>
> "If the upper element is not present or assumed, then the element cannot
> be assumed."
>

I think the current wording of that statement is a little ambiguous and
it's not entirely clear that master elements should not be assumed. If
mandatory master elements were to be assumed when absent, then it would
change what should be done. Perhaps some wording indicating master elements
should not be assumed could be added?

So…
>
> > Consider, for example, the ContentEncoding element. It's mandatory,
> > and its children have appropriate default values such that a
> > ContentEncoding element of zero size is perfectly fine. Now, taking
> > things a step further, could this ContentEncoding element be
> > completely removed from the bitstream? Or is it required to be present
> > in the bitstream?
>
> If it is absent then all of its children must be assumed to be absent as
> well. And that's how today's parsers work, too.
>
> Therefore EBML should specify it the same way.


Okay, that make sense. It would be great to see that reflected in the EBML
spec.

Thanks!
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