I am working on videos with alpha channel to be merged with a background video at a given position (for instance, [100,100]) . You can accomplish this by using:
ffmpeg -i BACK -i OVER -filter_complex overlay=100:100 OUTPUT
But I would like to test the result without having to generate the whole video and then playing it.
I've tried VLC but its only overlay option is to put a picture (not even animated) over the video. I don't know if there is a shader in MPC-HC that would suit me, but I haven't found it (and shaders, even simplest, are usually CPU demanding). The same happens with avisynth: the playing is jerky and seeking even worse (I believe it's because avisynth works with and outputs uncompressed video).
Is there a way to watch the resulting video on-the-fly, being able to jump to any point of it and using a reasonable amount of CPU?