[vdr] Re: vdr2divx suggestions ? (poll)

[ma.hoff@t-online.de (Martin Hoffmann)]

Am Mittwoch, 30. Oktober 2002 22:33 schrieben Sie:
> ----- Original Message -----
> From: "Martin Hoffmann" <ma.hoff@t-online.de>
> To: <vdr@linuxtv.org>
> Sent: Wednesday, October 30, 2002 11:32 PM
> Subject: [vdr] Re: vdr2divx suggestions ? (poll)
>
> > [...]
> >
> > > > > wrong, since 480x576 isn't a resolution in which videos appear on
>
> dvb.
>
> > > > Huh ?
> > > > See RTL and Premiere for instance ! They all cast with 480x576 !
> > >
> > > For sure, but the picture can't be in that format. At least it must be
>
> 4:3
>
> > > and 480:576 is  ... strange for mpeg4. Maybe the stream is in that
>
> format,
>
> > > they have added some black borders or stretched the picture or ..don't
> > > know. Will do a research on that topic till tomorow evening , Ok ?
> >
> > No !
> > they cast mpeg2 and mpeg2 (i guess all mpeg formats - even mpeg4) contain
>
> an
>
> > aspect ratio field - so they cast 480x576 with an aspect ratio of 4:3 -
> > telling the output device (DVBs card or stand alone receiver) - to scale
>
> the
>
> > picture to 4:3 - in square pixels (like AVI does it) this would be
> > 784x576
>
> !
>
> > No black border magic - just stretching the image ! Beside that is how
>
> 16:9
>
> > casts work - they have the full resolution if you have an 16:9 TV !
> >
> > However, as said above, AVI cannot store aspect ratio info - AVI always
>
> have
>
> > sqare pixels by default - thats why you have to scale to be avi
>
> compliant -
>
> > however if you intend to view your avi on TV keeping the 480x576 and
> > rescaling this at viewing time is okay !
> > Did anyone understand this ?
>
> Yes, but it would be fine to check the aspect-ratio in the MPEG-PES-stream
> and rescale when encoding.
For 16:9 this is already done in the vdr2divx scripts !
Now tell me how this can be achieved for 4:3 streams ?
In case we have a 4:3 stream with 480x576 resolution: Should we scale up to 
784x576 ? Producing lot's of redundant information and giving the codec too 
much data for the given bitrate !? Or should we scale down to 480x360 (also 
4:3) and loose lots of details !??
I prefer to keep the resolution of 480x576 and have the DVBs card rescale by 
replaying - thus keeping the original quality !
However i understand that if you target on PC replay the scaling to 480x360 is 
an option - so i will add this aswell, later on !

The main problem is the good (?) old (!) AVI format which has no field for 
aspect ratio !

Martin


-- 
Info:
To unsubscribe send a mail to listar@linuxtv.org with "unsubscribe vdr" as subject.