Is there a program or an option in Musicbee itself to batch compress every image in every audio file down to a specific resolution?
Yes, there is an option in MusicBee to do so. But it only becomes available when performing a sync operation between your pc and a device.
In the device settings under Artwork Storage, you can tell MusicBee what resolution to embed the artwork at.
After doing the sync, you would have to retransfer (and overwrite) the device music files back to your pc originals, and then ensuring that you rescan all of them in MB afterwards.
(select all > right-click > send to > file rescan).And all this is assuming you already have the original hi-res album covers stored somewhere else other than in the music files themselves before doing all this!
It'd be perfect if they were already stored along with your pc music files as cover.* or whatever naming syntax you've chosen for them.
But in case they aren't, then you'll first have to convert them to "organised copies" through a sync and using the "copy" options under the same Artwork Storage device settings.
All that would be left after rescanning your library is:
- going to your Preferences screen > Tags (1) > under artwork...edit list.
- choosing the naming template that your image files are stored as.
- then hitting "rescan artwork".
Try this on an album or two before working on the whole library.
And you said you have a backup of your library...which is good, in case things don't work out for whatever reason.
That's not a proper and straightforward "guide" as such, but it's how I personally would do it in MusicBee.
I'd also like to be corrected on anything I may be mistaken about in the steps I've provided (to what I think should do what you're asking).
Please also mention if there's a step you need clarity on before making an attempt.