Haha yes, I use it regularly! And yes, it'll be plenty fast on your system. I have very deliberately gone over the code base looking for inefficiencies six times now, so it runs nice and lean - I do an efficiency/hygiene pass every couple of releases to make sure bloat doesn't creep in.
As ark3@lemmy.dbzer0.com said, CPU encoding is slow but it preserves the most quality. No kidding, it really is night and day compared to GPU encoding - for this, just tick "Precision mode" in HISTV. It's about 1x speed on most videos, so a 45 minute file will take about 45 minutes.
GPU does go a lot faster, my 7900 XTX rips through 1080p at about 28x speed so a 45 minute file takes about 2 minutes. This is good enough for most content; just untick "precision mode" and set the multiplier to 2x or 3x with a bitrate of 4 if you want better GPU quality in HISTV. The multiplier says how high the peak bitrate can go, so you keep more data for fast-moving scenes, without forcing the encoder to keep useless data for slow scenes.
Yeah, it's early and I was just skimming the docs for it as I don't have a Mac. I'll think about the metadata downloader; it does have a place, arguably, as related to the mkv tag repair I built in.
As to the CLI, HISTV does have one! It's a standalone binary but it uses the same Rust backend as the GUI for feature parity and maintainability 😊