The tracking is basically a greedy search of the least sum of square differences of pixels in anchor, so even simpler than that.

I'm also interested in the GIF export. Right now I'm only exporting videos using canvas record stream, but I'm thinking about using ffmpeg.js to support different formats including animated gifs

I work for PaperlessPost.com, and for our Flyer product we export mp4s from ffmpeg compiled to WASM, which is similar to ffmpeg.js but optimized for our use case which sounds similar. We have this WebAssembly method working well but iOS 15 (and the other major browsers) now support MediaExporter which might be a better way to go if you have something else to convert these files. This becomes and issue because you can't control the format MediaRecorder is recording to but the management of memory, the image quality, the compression, the performance hit will be more ideal than these other methods. OMGgif is very slow and will produce large files or very bad looking ones. Keep in mind that GIFs limit the colors so something that looks nice on the screen might not look the same after it is saved. The other thing to look out for is the WebCodecs APIs which should be the ultimate way to handle all of this in the future but it is only working in Chrome I think https://github.com/w3c/webcodecs

I've tried using ffmpeg but the browser support just isn't very good yet, so I'm using https://github.com/deanm/omggif.