[MPlayer-users] Transcoding from one aspect ratio to another

[Nix]

On 2010.11.04. 03:24, Rolf Ernst wrote:
> On 11/3/2010 7:56 PM, JD wrote:
>> On 11/03/2010 05:44 PM, Rolf Ernst wrote:
>> Hey guys - let us not belabor this enquiry.
>> I accept that what I want cannot be done without one of
>> 1. Black bars on top and bottom
>> 2. Zoomed in until each frame fills 800 vertical pixels of the screen,
>> and then cropped so that only 1280 horizontal pixesl of the zoomed
>> frames remain.
>> Neither of these is what I want, so let's not continue to beat a dead 
>> horse :)
> This is simply not so but by all means, I shall not force you to 
> accept the facts.
Since my weekend started this evening you are welcome to prove it. No 
seriously, take a square (for sake of example you can assume that it has 
an image mapped on it) that's being displayed with ratio of 2:1 (in 
other words the image mapped on it is in fact stored in an vertically 
stretched state for improved vertical resolution). Now, if you crop 
away, say, 20% from right side, do you really think that it should be 
still be displayed with DAR of 2:1? Obviously, if you retained PAR, then 
all is fine but DAR would still be different. I don't know about 
mencoder but generally for muxing you need to specify either DAR or the 
intended viewing resolution which more or less obviously same thing.
P.S. I just found this cute little line in mkvmerge manpage:
"Matroska™ files contain two values that set the display properties that 
a player should scale the image on playback to: display width and 
display height."
P.P.S. Regarding your other post about anamorphic being non-square 
pixels, I'm not so sure about your definition. Mostly because anamorphic 
video was invented like before 1930's when digital computers didn't even 
exist, therefore at the very least your definition that ties anamorphic 
with PAR is at the very least badly defined, in my humble and worthless 
opinion obviously.
Cheers,
nix