Fair, it’s indeed a shame if there aren’t lossless or very-high-bitrate lossy recordings available. A literal sequence of PNGs is of course an upper limit, using temporal coherence (of which there’s a lot of) would shrink the size to maybe a few tens of megabytes. But of course there aren’t many lossless video formats in common use because it’s a rather niche use case outside mastering and archival. There’s lossless H.264 and H.265, and IETF’s FFV seems pretty well-supported too. Not sure if browsers support them though.