[FFmpeg-devel] New patch for mpegts.c

Michael Niedermayer michaelni at gmx.at
Wed Oct 24 05:38:54 CEST 2012

On Wed, Oct 17, 2012 at 05:51:28PM +0100, JULIAN GARDNER wrote:
> >>  Again we either process xxxx thousand sections or we do as the spec says 
> > and process only new/updated?
> > 
> > The spec doesnt say that, it says:
> >     d) version_number:
> >    -     When the characteristics of the TS described in the SI given in the 
> > present document change (e.g. new
> >          events start, different composition of elementary streams for a given 
> > service), then new SI data shall be
> >          sent containing the updated information. A new version of the SI data 
> > is signalled by sending a sub_table
> >          with the same identifiers as the previous sub_table containing the 
> > relevant data, but with the next value
> >          of version_number.
> >    -     For the SI tables specified in the present document, the version_number 
> > applies to all sections of a
> >          sub_table.
> > 
> > That speaks about "when X then ... shall be sent ...", sending happens
> > on the muxer side, not the demuxer. The text quoted says nothing about
> > what a demuxer should or should not do with what it receives. It
> > simply describes what a demuxer can expect from a valid DVB stream.
> > A concatenated stream as you already explained is not a valid DVB
> > stream ...
> So your now saying that the spec is only for the muxer, can you show me the spec for the demuxer then that is different, again i come back to the "New version .... but with the next value of version number". This spec if for DVB compatible systems, both muxers and demuxers.

The spec describes DVB streams, it says when a version field MUST
change. This requires a muxer to change the version field in such
cases so that its output is a correct DVB stream.

It does not require a demuxer to read that version field, or discard
the previous nor the next section with matching version.
Instead it gives a demuxer the OPTION to skip any of 2 sections with
matching version (because they are required to be the same).
The demuxer CAN skip it in case of a sequentially
demuxeed valid DVB stream. The demuxer CAN skip the first of 2 such
sections or it CAN skip the second or it CAN skip neither. All these
are valid behaviors.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Republics decline into democracies and democracies degenerate into
despotisms. -- Aristotle
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