[FFmpeg-user] Stream specifier ':v' in filtergraph ... matches no streams. (Seeking help on parsing output)

[Lou]

On Thu, 11 Jul 2013 15:07:30 -0700
John Crossman <johncrossman at berkeley.edu> wrote:

> Can you help me understand the problem?  (Thanks)
> 
> *The command:*
> 
> /usr/bin/ffmpeg -i audio.mp2 -i screen.mp4 -filter_complex
> [1:v]pad=iw*2:ih[bg];[bg][0:v]overlay=W/2+((W/2-w)/2):(H-h)/2 -qscale:v 2
> -strict -2 output.mp4

[0:v] does not refer to any stream. Your first input is audio only. I
assume you probably meant to use [1:v].

Note that, in your case, libx264 will be used for mp4 output, but this
encoder ignores "-qscale:v", so the default of "-crf 23" will be used
instead:

FFmpeg and x264 Encoding Guide
https://trac.ffmpeg.org/wiki/x264EncodingGuide