[MPlayer-users] MPlayer-1.0pre8 detecting wrong aspect ratio

[Giacomo Comes]

On Mon, Jul 31, 2006 at 10:31:18PM +0200, Nico Sabbi wrote:
> Giacomo Comes wrote:
> 
> >I have done more test. Without using -mpegopts vaspect=4/3 now 
> >the aspect is set correctly in the stream:
> >aspect 8 for 4/3 PAL and aspect 12 for 4/3 NTSC. This is the same result 
> >you have if you use mjpegtools in order to create the mpeg1 stream.
> >
> >Nevertheless pre7 plays the file with the correct aspect ratio and pre8 
> >don't.
> >
> >Giacomo
> >
> try to use -vf scale=100:200 -lavcopts vcodec=mpeg1video:aspect=4/3 and 
> see what happens :)

Let's try to clarify the situation.
I understand that you are now using in order to determine
the aspect ratio the pel aspect ratio of the mpeg1 standard:
3   0.7031   16/9 PAL
6   0.8437   16/9 NTSC
8   0.9375   4/3  PAL
12  1.1250   4/3  NTSC

and you determine the aspect ratio using the exact coefficent
present in the second column.
But it is the proper way to do it?

Let's consider an example.

PAL VCD is encoded at 352x288.
When you watch the VCD on a (4/3) TV, the video is expanded to fit
the displayed aspect ratio: 384x288.
This is how mpeg2 is handled.
For mpeg1 now mplayer expand the video to (352/0.9375=376) 376x288.
The aspect ratio is not anymore 4/3 but 13/10.
It means that if I make an mpeg stream and I connect my computer to a
TV and I use mplayer to watch the movie, the result will be a little
bit different if I encode to 352x288 mpeg1 or 352x288 mpeg2
because mplayer will play the mpeg1 movie with 1.30 A/R and the mpeg2 movie
with 1.33 A/R.
In my opinion this should be considered wrong.

PAL  352x288 mpeg1 (aspect 8)  should be played as 384x288 (Movie-Aspect 1.33:1)
                                            not as 376x288 (Movie-Aspect 1.30:1)
NTSC 352x240 mpeg1 (aspect 12) should be played as 352x264 (Movie-Aspect 1.33:1)
                                            not as 352x270 (Movie-Aspect 1.30:1)
PAL  352x288 mpeg1 (aspect 3)  should be played as 512x288 (Movie-Aspect 1.78:1)
                                            not as 500x288 (Movie-Aspect 1.74:1)
NTSC 352x240 mpeg1 (aspect 6)  should be played as 426x240 (Movie-Aspect 1.78:1)
                                            not as 418x240 (Movie-Aspect 1.74:1)

I know it's a bit confusing but I hope I was able to explain what I meant.

Giacomo