Default is ffmpeg.wasm — fastest for most sources, especially with
multi-threading. Enable this to use the browser's video decoder
instead, which lets you watch the source playing during conversion.
Best for short clips; some codecs (HEVC, AV1 without HW decode) may
fall back to ffmpeg automatically.
Auto-enabled when Chromium hangs on multi-threaded decode
(
ffmpeg.wasm #772,
open since 2023). We watchdog the first 10s of every decode; if
no frames land, we flip this on and remember it for next time.
Uncheck to retry multi-threading (e.g. after the upstream bug
is fixed, or on a different machine).