[FFmpeg-user] "Four up" output?

[Simon Roberts]

I'm now able to take four input streams from my Blackmagic quad input card
and successfully map them into a single compressed output file. What I'd
like to do next is to "tee-off" a monitoring stream (literally for live
viewing). There are two features I'd like for this:

1) create a composite output that has all four of the inputs laid out one
per quadrant, so all can be seen on a single display

2) preferably simply send this output (in real time, probably obviously) to
a window on the host computer, which I can then position and resize like
any other window onto an actual display of my choosing.

Is this possible? And if it is, what docs will I need to read to understand
how to start on something like this?

Of course if anyone has a ready-to-hand command line that does this (I have
four streams that I use -map to send to the same output file), I won't turn
it down :)

Many thanks!
Simon