How to use with long (>1 hour) mp3s?

[sergueif]

Hello, I'd love to use the fingerprints so I can add metadata to my music in a separate system and have it survive changes in the file and re-downloads, etc. I'm a bit confused how to use fpcalc shell utility:

1. Do I need to do anything to the mp3 before using fpcalc on it? (i.e. ffmpeg decode it somehow) or is basic invocation like fpcalc <flags> FILE.mp3 ok?
2. -format flag. Would that be mp3 for mp3 files?
3. -rate flag. What are some appropriate values here? some of the files i'd love to fingerprint are long (1-3 hours) music sets, so would this cause fpcalc to "sample" a smaller amount of the file throughout? Not the most important thing but on long files, fingerprinting does take a while.
4. -channels. Can I leave this as default? most of the time I don't know (i guess usually it's 2).
5. -length. default 120 seconds doesn't seem right for a long mixtape. Can I set this to 9999 so that it covers whole file? or does 0 also cause it to not limit the amount of file?
6. -chunk, -algorithm, -overlap. Do I need any of those? how do they affect the fingerprint?
7. -raw. I read somewhere that this is needed if/when I'd like to compare fingerprints. Yes that's 100% of my use case. If I then wanted to make a fingerprint shorter (for personal library use), I can hash the raw fingerprint.

Using some guesses, I tried fpcalc -raw -length 9999 <FILE.mp3>. I then changed some ID3 tags on the file, ran fpcalc again, and fingerprint stayed the same. But after using "mp3Gain Express" (mac app to add REPLAYGAIN tags), ran fpcalc and fingerprint changed. what gives? I thought replaygain just analyzes and adds a tag, no change to audio?

Sorry for so many questions. Fingerprinting by acoustid is a super exciting tool and idea. I'd love to finally have a reliable way to attach metadata in other apps to something reliable like AcoustID. I just want to make really sure that the way I'm executing fpcalc is really robust to irrelevant changes to the file (changing tags, replaygain, album art, file rename, etc.). Fingerprint should stay the same when the audio still sounds the same.