[FFmpeg-user] stopping ffmpeg correctly while piping

[Gyan Doshi]

On 1/12/2018 12:14 AM, Moritz Barsnick wrote:
> 
> Apparently, this requires you to explicitly map something ("-map 0"). I
> don't recall why, and why not with a filter involved. Too lazy to
> contemplate. *shrug*

My guess is, in absence of map, ffmpeg auto-selects streams for output 
based on what the muxer accepts i.e. image2 muxer won't accept audio. 
But the tee muxer isn't an actual format and the child muxers aren't 
"seen" when configuring output streams, so map is required. And all 
filtergraph output sinks are automatically designated for output, 
regardless of muxer. This doesn't apply to simple filterchains (vf/af) 
which act on - expressly or implicitly - mapped streams.

Regards,
Gyan