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

Rolf Ernst rolf.ernst at silverlightning.org
Thu Nov 4 01:54:23 CET 2010

On 11/3/2010 5:30 PM, JD wrote:
> On 11/03/2010 03:26 PM, Nix wrote:
>> On 2010.11.03. 18:06, JD wrote:
>>> I have a video file that has an aspect ratio of
>>> 2.353 : 1
>>> I would like to transcode it to an aspect ratio
>>> of 1.6 : 1 (like 1280x800).
>>> Is this even possible?
>> It's been a while since I lasted had to encode a video and truth be 
>> told I was never that good at it but generally speaking you can 
>> change how video is represented internally by messing with PAR and 
>> actual resolution and/or by cropping and adding black borders change 
>> it's "physical" form (DAR) (do note that this might crop away needed 
>> information, also if it was anamorphic you will need to recalculate 
>> the correction factor).
>> Short answer: just like you can't inflate or deflate a rubber balloon 
>> with a picture on it and expect that picture to stay undistorted, you 
>> generally can't change image form without cropping some of it or 
>> squashing it, which is what you want, if i understand correctly.
>> Regards,
>> nix
> Yes - I now see that.
> I was hoping that the technology might provide something
> similar in concept, but not identical to, slowing down or speeding
> up an audio while keeping the sound frequency unchanged.
> But I resign :)
> I will leave it as is.
JD, I am not sure why you are resigning. I think your question is not 
quite clear and the various responses have outlines all sorts of 
mechanisms of doing what the authors surmised you wanted to do. The 
majority of video format arguably works with *non-square* (anamorphic) 
pixel sizes. For example, the DV format has a 0.09:1 pixel size.

Folks have now outlined how to generate an image of the resolution you 
desired, shown you a way how to generate this image by adding black 
borders and thus using square pixels or using anamorphic picture sizes 
(and no - there is absolutely no calculation required to keep the 
display aspect ratio when rescaling to different sizes although mencoder 
gives you the *option* to override this any which way you want).

If this still isn't clear: I know there are countless others but my GUI 
frontend YAMF (http//www.24hourloop.com, it's in Java) allows you to 
specify any output resolution you want while maintaining aspect ratio 
(go to filters->scale). It is designed to work with x264 but you can 
copy and paste the command line and change it to use another codec manually.

Anyhow, from what I can tell every option in the book has been 
demonstrated and I cannot possibly see what option may be missing. So, 
despite your conclusion, whatever it is you want to do can be done with 
mencoder. If it is still not clear which options you should use maybe 
you could more clearly explain what it is that you want. Maybe we just 
didn't understand your question in the first place.

Again, every conceivable interpretation of your question is easily and 
elegantly done with mencoder. No reason to give up.


"My friends, watch out for the little fellow with an idea"

Tommy Douglass

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