If you use ffmpeg’s libavcodec interface then you can get it to give you the decoded framebuffers as exported DRM-prime descriptors which you can turn into textures. This is how Firefox does video decode with VAAPI, using libavcodec as a wrapper.

Edit: missed the part about JS ecosystem. You can move DRM prime descriptors between processes, but I assume you can’t do this from the ffmpeg CLI and would need to write your own little C wrapper around libavcodec