Re: [mpeg2-dev] Mpeg question

[Christophe M. <ma...@vi...>]

On Tue, Nov 06, 2001, Burkhard Plaum wrote:

> Now, I want to write some code, which gets the total number of audio-
> and video streams contained in the file. The question is, what is the
> best way to do this? Parsing the system header gives numbers,
> GREATER OR EQUAL to the numbers of audio/video streams, and there
> are also files, which have no system header at all (but are played
> nicely e.g.
> by libmpeg3). Parsing the whole stream would give exact results, but it
> takes
> too long and is impossible, if the input source isn't seekable.
> 
> Is there a way to obtain the number of PES packets (or bytes), which
> have to
> be parsed until there was at least one PES packet from each stream? I
> should
> also note, that this should work for mpeg1 and mpeg2 program streams.

Unfortunately, what you want to do is impossible. A new stream can begin
anywhere in the file. The strategy we used in VLC is to preparse the
first 5 MB of the file and add streams that begin thereafter "on the fly".
But that's not what you want to do.

DVDs have .ifo files for that purpose. MPEG-2 also has a structure named
Program Stream Map which does exactly what you want (map all elementary
streams). Unfortunately, most MPEG streams don't have this structure.

I haven't found a better way in VideoLAN...

-- 
Christophe Massiot.