I'm working on porting ffplay, targeting HEVC but also all the other decoders if possible. I've had nothing but trouble from emscripten and have had to start from the beginning, just using ffplay as reference and very slowly building the application up.

Emsriptens proxy_to_thread option doesn't transfer the document context correctly, so calls from SDL to change canvas size, mouse scroll events, etc, all error. I just had to comment those lines out.

But then the program would infinitely lock because a mutex would not return when a pthread was created. It would just spin on mutex.wait, and there were no errors in the thread creation as I tracked it line by line.

Then debugging randomly wouldn't compile anymore.

There's a whole blog I'll write on it but the summary is that emscripten is cool, but the quality of it's features isn't ready to simply cross compile without the underlying code supporting it.