Video mosaic FAQ: speed, quality, and file size
Why mosaic is slower than trimming, how quality is controlled, and how large a file you can process in the browser.
Mosaic applies filters and re-encodes; it cannot stream-copy like a simple trim, so it takes longer.
Output uses H.264 with selectable CRF quality (high / balanced / small) and tries to keep the original audio.
Processing runs in WebAssembly with a soft 1GB cap; hundreds of MB is more reliable.
Download the result promptly — refreshing clears temporary files.