[FFmpeg-user] New To FFmpeg streaming question

[Moritz Barsnick]

On Fri, May 22, 2015 at 19:45:34 -0500, Orion Fyre wrote:
> 
> > ffmpeg -i "udp://@225.1.1.15:4454?fifo_size=640000&overrun_nonfatal=1" -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:
In
  "trunc(oh*a*2)/2:480"
oh in effect refers to the 480. So the width is a function of the
output height. Perfectly fine.

In the expression you recommended:
  "trunc(ow*a*2)/2:480"
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.

Moritz