[FFmpeg-user] Stream specifier ':a' in filtergraph Error

[Michael Koch]

Am 10.11.2020 um 22:27 schrieb Randy Johnson via ffmpeg-user:
> Hello,
>
> When running the following command:
>
> ```
> ffmpeg \
> -loop 1 -framerate 30 -t 1.4 -i /assets/img/filler640480.jpg -i 0d.mp4 -
> y \
> -loop 1 -framerate 30 -t 891.113 -i /assets/img/filler640480.jpg -i
> 9f.mp4 -y \
> -f lavfi -t 0.1 -i anullsrc=channel_layout=mono:sample_rate=48000 \
> -filter_complex "
> [0:v]setsar=1[v0];[2:v]setsar=1[v1];[v0][4:a][1:v][1:a][v1][4:a][3:v][3:a]concat=n=4:v=1:a=1"
> -vsync 2 -vcodec libx264 -pix_fmt yuv420p 0245-grid.mp4
>
> ```
>
> I am getting the following error:
>
> ```
> Stream specifier ':a' in filtergraph description
> [0:v]setsar=1[v0];[2:v]setsar=1[v1];[v0][4:a][1:v][1:a][v1][4:a][3:v][3:a]concat=n=4:v=1:a=1
> matches no streams.
> ```
>
> This only happens on some video processing not all, cannot seem to
> figure out why.

You could check those videos with FFprobe. May be they have no audio 
stream, or something else is different.

Michael