[linux-dvb] Re: TS tables doubts

[John Dalgliesh <johnd@syd.microforte.com.au>]

On Fri, 18 Jul 2003, Nico wrote:

> 
> Hi,
> 
> as far as I understand, in order to find what channels are
> transmitted on a given full TS I have to follow these steps:
> 
> 1) read the PAT to find the list of programs ids
> 2) read the PMT to find the list of ES streams (audio/video/teletext/subs)
> associated to a given program id
> 
> Is it correct?

Yes.

> Now I wonder
> 3) what's the use of NIT and SDT?

The NIT gives you info about the network, e.g. network name, plus
transport settings for that network (which you already had to know to be
receiving it :)

The SDT gives you the names of the 'channels' i.e. a name for each 
program id (MPEG-speak) / service id (DVB-speak).

> 4) reading VLC's demuxer it seems that there's a tables describing the
> type of each elementary stream (e.g. video is M2V, audio is MP2 or AC3
> 2.0 or AC3 5.1); what table is this?

AFAIK there's no single table for it, you have to figure it out from the
stream type and other stuff.

e.g.
stream type 1 => mpeg 1 video
stream type 2 => mpeg 2 video
stream type 3 => mpeg 1 audio
stream type 4 => mpeg 2 audio

stream type 6 => private, look in PMT descriptors for say an AC-3 
descriptor, which tells you that it's an AC-3 stream and what kind of AC-3 
is in it.

You can also get some info from the stream id ... e.g. mpeg video 
0xC0-0xDF, mpeg audio 0xE0-0xEF (maybe, or around the other way). AC-3 
audio is in 0xBD, but you need to check descriptors to be sure.

You can only figure out the stream id once you've got some packets on that 
stream, it isn't in the PMT.

> 
> Thanks very much,
> 			Nico

Hope this helps.

{P^/



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