[FFmpeg-user] New To FFmpeg streaming question

[Cooper_Benjamin]

Thanks for the comments so far.  I feel like I am starting to understand what these expressions mean.  However, I am still a little lost on the two errors that popped up originally:
- [mpeg2video @ 0000000000396840] Invalid frame dimensions 0x0.
    Last message repeated 11 times
- http://localhost:8080/myTest.mp4: Unknown error

If it helps any, I can do something similar with VLC using the following command:
vlc --sout-keep --ttl "1" --no-sout-standard-sap --no-sout-rtp-sap --screen-fps "1.000000" --screen-caching "100" --sout #transcode{vcodec=theo,vb=800,acodec=mp3,scale=1,width=600,height=480}:http{mux=ogg,dst=:8080/myTest.ogg}" udp://@225.1.1.15:4454

I do realize that the VLC command is converting the UDP stream into an ogg file and in the FFmpeg command, I was attempting to convert the UDP stream to an mp4 file.  

Am I on the right track with the FFmpeg command or should I be trying something different?

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


Ben Cooper

-----Original Message-----
From: ffmpeg-user-bounces at ffmpeg.org [mailto:ffmpeg-user-bounces at ffmpeg.org] On Behalf Of Moritz Barsnick
Sent: Sunday, May 24, 2015 4:45 PM
To: FFmpeg user discussions
Subject: Re: [FFmpeg-user] New To FFmpeg streaming question

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
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