Alright, here's the alternative: code an extension that implements a video codec. Due to speed considerations, this will likely need to be done in native code for every platform you choose to release to. Then, you'll need to test to make sure it's working properly.
Also, you need to make sure that the video codec you're implementing isn't proprietary. If it is, prepare for lawsuits.
You might be able to use FFmpeg, but it's possible that if you do, you might have to release your game under either GPL or LGPL (meaning that you're obligated to release the source code of the game to anyone who asks you).
I will point out that implementing video codecs is a very difficult task. Doing it in a performant manner is even harder. It would be easier, safer, and cheaper (in terms of opportunity cost) to buy the extension on the marketplace.