[FFmpeg-user] change inputs or mapping while recording

[Michael Koch]

Am 24.04.2020 um 20:08 schrieb Edward Park:
>> I would now like to add stream2 as second video input and switch
>> between stream1 and stream2 back and forth without interrupting the
>> audio. Both streams are identical / come from identical cameras.
>>
>> Is there any sane way to do this with ffmpeg? Or how would you
>> recommend doing it?
> If I had to do this, I would basically composite the two streams and toggle opacity of the top layer between 0 and 1.
> It would break if either stream had reading problems, and you would constantly be processing both streams which might not be desirable if you were switching from A to B and never go back to A, for example.

How can this be done with FFmpeg? Do you have an example? I know how 
commands / sendcmd works. The opacity could be toggled, or the 
streamselect filter could be used. But where does the switching signal 
come from, while FFmpeg is running?

Michael