[FFmpeg-user] Changing DAR ?

[Ronald F. Guilmette]

In message <loom.20131008T121902-356 at post.gmane.org>, 
Carl Eugen Hoyos <cehoyos at ag.or.at> wrote:

>Ronald F. Guilmette <rfg <at> tristatelogic.com> writes:
>
>> I am trying to use ffmpeg (2.0.1) to make what I believe 
>> should be a simple change in a video file I have, and 
>> it's just not happening, so I need to ask what I am 
>> doing wrong.
>
>Please post your command line together with the complete, 
>uncut console output.


Thank you.  I would, but it might be embarassing. (1/2 :-)

But seriously, I've (now, finally) managed to get done what I wanted to
get done, as far as manipulating the aspect ratio(s) in the actual video
file, but as I described at some length in my immediately prior posting,
the documentation of this stuff could use some improvement.

As I mentioned, earlier I had tried this, which did not seem to have
any effect at all:

    ffmpeg -i foo.avi -acodec copy -vcodec copy -vf setdar=16:9 bar.avi

Now I have tried instead:

    ffmpeg -i foo.avi -acodec copy -vcodec copy -vf setdar=16/9 bar.avi

the subtle difference being the use of a '/' instead of a colon when
specifying the desired DAR.  Anyway, that seemed to work, although
going by the examples here:

     http://ffmpeg.org/ffmpeg-filters.html#Examples-19

it should not have, because I neglected to insert also a "dar=" or
"ratio=" sub-sub-clause.

I understand now that within the arguments given in/for the setdar and
setsar sub-options, when it is desired to express a ratio, that ratio
must be written in the form:

	numerator/denominator

and now that I've looked at the examples located at the URL just above
I can even understand why this is necessary (i.e. because colons are
used as sub-sub-option delimiters/separators, so they can't be used within
the actual arguments given for the sub-sub-options) but still, I could
have sworn that I had seen some examples somewhere which showed ratios
of the form:

	numerator:denominator

being used or specified within some different ffmpeg options (or sub-options).
If so, then I'd like to just re-assert that it is quite confusing to the
end-luser (like me) to have to write ratios in different formats, depending
in the specific context within the ffmpeg command line one is dealing with.


Regards,
rfg