[Matroska-devel] VobSubs in Matroska

Moritz Bunkus moritz at bunkus.org
Wed Oct 29 08:56:03 CET 2003


> I agree, now is the time to make it right. Just some things :
> - how big is the overhead introduced by the MPEG PS ?

Significant. In VobSubs, each block has a size that is a multiple of
2048 bytes. 32 are MPEG headers, 2 and the end some other stuff, and if
the SPU packet is smaller than the rest then filling is used. So the
overhead may be somewhere between 34 and a LOT more. Maybe I can give
you some figures for a VobSub tonight.

> - if we leave it like we have it now, will it be easier for other apps 
> or hardware devices to support this with the MPEG PS ?

No. Every Matroska demuxer would also need a basic MPEG PS demuxer in
order to get the SPU packets. Things like timestamp, track ID etc are
available from the Matroska container anyway.

> - when demuxing it from the MKV, can we restore the original .sub file
>   ?

Very likely, yes. Just recreate the MPEG PS stream. It will not be the
original stream but very close. Not original because the track ID is
stored in the stream and that one gets lost because we use our Matroska
track numbers, but that's a minor issue and not worth keeping the
overhead and complexity.

 ==> Ciao, Mosu (Moritz Bunkus)

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