Hey Lieff, thanks for this library and minimp4, I'm compiling them to WASM for the web here using Emscripten and it's working well.

Something that came up is a filesize concern. I did a quick test with 30 1920x1080 frames of Big Buck Bunny and the resulting MP4 is 11MB (gop=20, speed=0, qp_min=10, qp_max=10). But, using that output MP4, running default ffmpeg -i vid.mp4 vid2.mp4 produces a 181KB file. Is there something I might be doing wrong in minih264 that would produce such high file sizes compared to ffmpeg's default encoders?