[foms] Chunks

Andoni Morales ylatuya at gmail.com
Thu Nov 11 06:29:58 PST 2010

2010/11/11 Steve Lhomme <slhomme at matroska.org>:
> On Thu, Nov 11, 2010 at 11:17 AM, Pierre-Yves KEREMBELLEC
> <pierre-yves.kerembellec at dailymotion.com> wrote:
>> Well, if carefully designed, such intelligence can prove very useful to reduce the number
>> of files effectively. See here for an example of such implementation:
>> http://lists.annodex.net/cgi-bin/mailman/private/foms/2010-November/000894.html
>> http://lists.annodex.net/cgi-bin/mailman/private/foms/2010-November/000936.html
> Interresting. To clarify things on the MKV/WebM side that you don't
> support yet. I think it's easier to send Matroska chunks on the fly
> that MP4. Basically these chunks don't need a Cues section (nor
> chapters, tags, etc or even Meta Seek). So the header is fixed and the
> same for all chunks (all you need it set an "unknown" on the high
> level Segment structure). They copy as much Clusters you need from the
> source file. I think that's basically what Fluendo/GStreamer are doing
> on their HTTP server of live WebM content. They don't even bother
> cutting the source file on Cluster boundaries, but in the case of
> chunks that are supposed to join correctly, you want to avoid some
> false alarm in trying to find the boundary you want.
On GStreamer, the webm muxers starts a new cluster for each keyframe
and unset the DELTA_UNIT flag on this buffers, which makes it a
"keyframe". The streamer, multifdsink, allows syncing new clients
connections on keyframes, so a client will always receive a stream
completely decodable.

> If you look at this document: http://www.matroska.org/technical/order/index.html
> You only need Segment Info, Track Info, Clusters. These are all
> contained in a Segment, which can have an undefined/infinite size. So
> the server doesn't have to cache data in memory to know the exact size
> before "closing" the Segment. Same thing for all the Clusters,
> although they should typically match those of the original WebM file.
> Plus Clusters are usually around 2s and for WebM the video should
> start with a keyframe, so no extra logic needs to be applied here.
> This kind of simplistic files/chunks will work fine in any known
> player Matroska players.
> Steve
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Andoni Morales Alastruey

LongoMatch:The Digital Coach

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