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

Dave Rice dave at dericed.com
Tue Sep 29 03:35:11 CEST 2015


Hi Michael,
Just answering the ones where I’m fairly certain of the answer.

> On Sep 28, 2015, at 9:03 PM, Michael Bradshaw <mjbshaw at google.com> wrote:
> 
> Hi! I'll launch right into my questions:
> 
> In the MKV spec, where it has examples for lacing, when it says "400 octets" does it mean 500?
> What’s the point of default values for non-mandatory elements in the MKV spec? Why not make them mandatory if they have a default value?
> Is the duration of a block always evenly distributed amongst its frames (for a block that has multiple laced frames in it)? I don’t see any explicit mention in the MKV spec as to how the block’s duration is supposed to be distributed to its frames, and I think that should be mentioned.
> How can the EBMLMaxIDLength be less than 4, when the EBML and Segment IDs are 4 bytes? Shouldn’t the EBML spec require the range to be > 4 and the MKV speck require it be exactly 4?
As you note the EBMLMaxIDLength can not be less than 4 because of the 4-byte EBML Element ID. You’ll see the description for EBMLMaxIDLength is clarified here: https://github.com/Matroska-Org/ebml-specification/blob/master/specification.markdown <https://github.com/Matroska-Org/ebml-specification/blob/master/specification.markdown> so that it doesn’t hint of less than 4 which is not possible. I think the understanding is that the Matroska spec can constrain the EBMLMaxIDLength to 4 (which means that 4 is the only valid EBMLMaxIDLength for the Matroska docType but another doctype of EBML could use a higher value.
> Are the "EBML Elements Order Guidelines <http://matroska.org/technical/order/index.html>" normative? The word "guidelines" in the title suggests no, these are merely suggestions, but the language (i.e. "must") used on that page sounds like it's intended to be normative.
> 
> Additionally, I have several questions of a similar nature regarding the EBML spec (including a typo); is the best place to ask those on the ebml-specification Github <https://github.com/Matroska-Org/ebml-specification>?

Yes this repository is where current work on the refinement of the EBML specification is underway. I think the understanding is that the EBML specification will be refined and then the redundant parts of the Matroska spec will be removed, so there there is an EBML spec and a Matroska spec with a dependency on the EBML spec.

Dave Rice

> Thanks,
> 
> Michael Bradshaw
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