[FFmpeg-user] New To FFmpeg streaming question

Moritz Barsnick barsnick at gmx.net
Sun May 24 22:44:39 CEST 2015

On Fri, May 22, 2015 at 19:45:34 -0500, Orion Fyre wrote:
> > ffmpeg -i "udp://@" -vcodec libx264 -preset slow -crf 20 -c:a libvo_aacenc -b:a 128k -vf scale="trunc(oh*a*2)/2:480" http://localhost:8080/myTest.mp4 
> >
> Your scale expression doesnt make sense. Its scale="width:height". For the width part of the expression you're usin 'oh' which stands for 'output height'. Did you mean to use the expression:
> scale="trunc(ow*a*2)/2:480"
> ?

Orion: Actually, it does make sense:
oh in effect refers to the 480. So the width is a function of the
output height. Perfectly fine.

In the expression you recommended:
the width is a function of the output width - now, that's impossible.
If you had tested your recommended expression, you would have seen:

Error when evaluating the expression 'trunc(ow*a*2)/2'.
Maybe the expression for out_w:'trunc(ow*a*2)/2' or for out_h:'480' is self-referencing.


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