Is it possible to compile FFmpeg for RIOT? What would the steps be to accomplish the cross compilation. My target platform would preferably be RPI-PICO
I think the answer is, technically, yes. But it would require significant effort and will be too large to fit any common MCU. Also, most MCUs would be way too slow to do anything meaningful with it.
What exactly is the use case you intent to address?
Maybe something like encoding a picture taken with a camera in a compressed image format to send over network? I personally would try to search for projects with a more narrow scope ideally with use on MCUs in mind, first. If none fits the bill, maybe only parts of the ffmpeg codebase relevant to your use case could be uses instead of porting it all?
My use case involves capturing video from an hdmi source and overlaying it with some text. It could definitely just use some subset of FFmpeg. I was trying to leverage the network stack etc that RIOT already has and for the video capture and text overlay use something like FFmpeg.
Interesting project I have seen DVI output (which can be send over HDMI wires) working smoothly with resolutions up to 640x480 even with two outputs, but I have never seen DVI capture.
I think the PIO state machines do also a good job at decoding digital signals. Maybe it is possible to indeed decode DVI signals after all. That would certainly be cool.