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

[JD]

On 11/03/2010 05:54 PM, Rolf Ernst wrote:
> 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.
>
Yes, I understand. I tried the solutions provided.
And I just responded that neither horizontal black bars
are what I want in the output, nor the cropping
of the frames from left and right (i.e. after zooming in
to make the frame fill 800 vertical pixels), which would also
expand the frame horizontally to well beyond 1280 pixels,
which in turn would require horizontal cropping to fit the
frame nicely in 1280 horizontal pixels.
All the solutions offered (that did not involves cropping) I tried,
and the result played with mplayer. I click on "Maximize
Window" square of the window manager's title bar, I end up
with what appears like a 4:3 aspect ratio, with the objects
being vertically elongated.

So, I will let it rest.

I do appreciate all of you who responded. I hope that other
people will benefit from the great information that has poured
out into this thread.

Best Regards and thanx to all,

JD