a

[hell001]

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[OrfiDev]

1. isn't that for cover images? Anyway, compression can be "disabled" by using PNG instead of JPG on supported cover modules, since that does lossless compression, whereas I'm pretty sure you physically can't not lose any data with JPG. Though I have no clue why you'd want to have such a massive file be embedded in the FLAC/whatever file itself, it can cause issues and that's what the external cover system is for.
2. ignore it, the advanced login system was supposed to add a feature from RedSea that was missing in OrpheusDL, but was never completed
3. yes, it's automatic based on the conversions you list out. Undesirable conversions are lossy-to-lossy and even worse, lossy-to-lossless.
4. it's an ffmpeg flag https://stackoverflow.com/a/44839083
5. when you use a separate cover module to the one you're downloading with for better or even original quality (or even with the Apple Music module, downloading the actual original file), it compares it to the cover from the original module, and if the difference found by the algorithm is greater than the threshold, the candidate cover is rejected.
6. see # 3 above.
7. in hindsight, a better name for it is probably skip existing file check, I never even thought about it being misleading
8. during artist downloads, in albums by other artists, this will skip all the songs not by the artist you are downloading
9. there are no public extensions iirc, but they're kinda like modules for modules lol