[Ffmpeg-devel] Sample Aspect Ratio & Pan&Scan

herve.flores herve.flores
Sat Nov 4 12:58:32 CET 2006


Le 3 nov. 06 ? 23:58, M?ns Rullg?rd a ?crit :

> Nico Sabbi <nicola_sabbi at fastwebnet.it> writes:
>
>> Nico Sabbi wrote:
>>
>>> it's something that left me some doubts, too.  If pan&scan is
>>> supposed to work with the intervention of the player (by means of
>>> cropping) shouldn't lavf export both the original par(without
>>> keeping into account the pan&scan) in
>>> AVCodecContext->sample_aspect_ratio and {width, height,
>>> pan_scan_par} in AVPanScan?
>>
>> I forgot to add that recently I've seen a huge amount of dvds (more
>> than 1 out of 2) played distorted by lavc because of this pan&scan
>> thingy
>
> I have a DVD that lies about the aspect ratio.  The IFO files say it
> is 16/9, and the MPEG2 sequence header says 4/3.  Watching the video,
> it is clear that 16/9 is correct.
>
> Could you please upload a few samples from the DVDs you mention?  I'd
> like to have a look at them.
>
> --  
> M?ns Rullg?rd

Just my opinion (I'm no dev, I'll don't talk about ffmpeg code):
DVDPlayer doesn't have the rght to use elementary stream (=mpeg2)  
aspect information = specifications (but some are doing it like the  
"kiss" dvd players :-(
the aspect information is in the wrapper (=mpeg) is not used too.
Only the aspect in the .IFO is allowed.
Then you can use 4/3 or 16/9 aspect in your elementary stream and a  
different one for your wrapper, and oanother differnet for your IFO  
(a lot of commercial dvd are doing it, for example Harry Potter 's  
elementary streams are all in 4/3, but displays are 16/9letterbox 
(=movie) or 16/9Pan-Scan(=menus)). With these complex disc authoring,  
even the .IFO doesn't reflect easily the used  aspect (they use  
variables to point to another .iFO too, not easy to read the useful  
display's aspect;-))

many sizes are allowed for dvd, and there is no real problem with  
anamorphic or square pixels: the player just crop 1/8e of the  
horizontal size of the source on each size is there is an pan-scan  
aspect. If your source is Widht 704, player will crop 704/8 on each  
size. If your source is 720, player crop 720/8 on each size.
The Pan-Scan aspect is allowed and manage by dvd-player, no utility  
with elementary stream, or wrapper, just IFO

last point (about SAR), something find on my Hard Disk (I didn't  
remember where I found it, I had a pb of display one time with VLC  
and I searched for info):
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these "info" are only for mpeg, I don't know DivX.
hope this help.

bye (and sorry for my english)

good continuation

Herv?



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