[linux-dvb] Re: Twinhan DST / TS204 and signal quality questions

[Måns Rullgård <mru@pronto.tv>]

Jukka Tastula <jukka.tastula@kotinet.com> writes:

> On Monday 16 August 2004 04:10, Måns Rullgård wrote:
>
>> What sort of documents was that?  I can't find any mention of I frame
>> intervals in the MPEG standards, but I may have missed it.
>
> Actually now that I think of it it wasn't any kind of general mpeg2 
> knowledge but encoder documentation and behaviour. For tmpgenc and cce to 
> be exact. They both had 15 as the highest you could select (for PAL 
> anyway) and those two being the most popular encoders I assumed this was 
> the limit. I'm guessing they made it so to prevent people from encoding 
> streams incompatible with DVD.
>
> Interesting how all the docs I can dig up say there are "restrictions on 
> the GOP structure" but don't bother mentioning what exactly these 
> restrictions are.

I found some information at http://www.mpeg.org/MPEG/DVD/Book_B/Video.html.
The interesting bits are:

  GOP size  max 36 fields or 18 frames (NTSC)
            max 30 fields or 15 frames (PAL)

and

  MP@ML has no GOP size restriction. In fact, the GOP() is considered
  to be an insignificant layer in MPEG-2. Instead the sequence() layer
  serves as the most important boundary in the generic MPEG sense.

The last bit could perhaps be deduced from the lack of mention of
limits in the ISO standard.

> We're way off topic here :)

Oh, I've seen worse.

-- 
Måns Rullgård
mru@pronto.tv