[FFmpeg-user] "showwaves has an unconnected output" when sending audio with waveform as video

[Moritz Barsnick]

On Tue, Jan 29, 2019 at 23:04:23 +0100, Zoltan Kerenyi Nagy wrote:
> Slight modification does not work either:
> 
> ffmpeg -f lavfi -i nullsrc -f alsa -i hw:0,0 -filter_complex
> "[0:a]showwaves=s=1280x720:mode=line:colors=Blue[v]" -map "[v]" -map 0:a
> -c:v libx264 -r 15 http://localhost:5554/video.ffm
> 
> error:
> 
> Stream specifier ':a' in filtergraph description
> [0:a]showwaves=s=1280x720:mode=line:colors=Blue[v] matches no streams.

This is why you should always show us the *complete* uncut console
output. You are hiding interesting info otherwise.

Your first input (0) is nullsrc, a video source. So "[0:a]" does not
specify a valid stream. You are not even using nullsrc, so you should
probably omit "-f lavfi -i nullsrc", then the rest should work.

Moritz