Client-side frame extraction is far too slow to be usable for large volumes of data.

You want to precompute the contact sheets and serve them to users. You can encode them with VP9, mux to IVF format, and use the WebCodec API to decode them in the browser (2000B-3000B per 240x135 frame, so ~3MB/hour for a thumbnail every 4 seconds). Alternatively, you can make the contact sheets with JPEG, but there are dimension restrictions, reflow is slightly fiddly, and it doesn't exploit intra-frame compression.

I made a simple Python/Flask utility for lossless cutting that uses this to present a giant contact sheet to quickly select portions of a video to extract.

Actually, I started with the precomputing approach you mentioned. But I realized that for many users, setting up a backend to process videos or managing pre-generated assets is a huge barrier.

I purposely pivoted to 100% client-side extraction to achieve zero server load and a one-line integration. While it has limits with massive data, the 'plug-and-play' nature is the core value of VAM-Seek. I'd rather give people a tool they can use in 5 seconds than a high-performance system that requires 5 minutes of server config.