[Matroska-devel] Proposal for a better definition for the 'keyframe' flag

Steve Lhomme slhomme at matroska.org
Sat Jun 15 16:54:43 CEST 2013


"frames" could be replaced with "laces" since that's what it contains,
regardless of the format (video, audio, subtitles, etc)


On Sat, Jun 15, 2013 at 4:01 PM, Jan Ekstrom <jeebjp at gmail.com> wrote:

> On Sat, Jun 15, 2013 at 3:12 PM, Steve Lhomme <slhomme at matroska.org>
> wrote:
> > When do you see the second definition in the specs ? I cannot find it.
>
> http://matroska.org/files/matroska.pdf (as I noted, the Matroska
> 'specification' PDF), page 39. Since the definition on the web page
> isn't exactly definitive, it leads to people looking for other
> definitions, like this one.
>
> > This SimpleBlock contains only random access point frames. When decoding
> > starts from a random access point, it can be correctly decoded, as well
> as
> > all the following multiplexed data in presentation order, without having
> > access to previous multiplexed data in coding order.
>
> I'm not sure if this is noted anywhere else, but as far as I can see
> this limits the SimpleBlock to contain a single "sample" (MPEG-4 Part
> 12 lingo), if this is how SimpleBlocks should be used, then this
> should be defined somewhere else as well, methinks?
>
> Also I am not sure about the wording of "contains only random access
> point frames", "This SimpleBlock consists of frames that form a random
> access point" is what I just came up with some thinking. A random
> access point is just a tag, you should not, if possible, limit its
> contents too much. Unless you want to define a whole lot of extra
> things like the formal part of 14496-12's random access point
> definition does, that is.
>
> For reference, the 14496-12's random access point definition:
>
> random access point (RAP):
> Sample in a track that starts at the ISAU of a SAP of type 1 or 2 or 3
> as defined in Annex I
>
> NOTE: Informally, a sample, from which when decoding starts, the
> sample itself and all samples following in composition order can be
> correctly decoded.
>
> Jan Ekström
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-- 
Steve Lhomme
Matroska association Chairman
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