When I add covers in FLAC files, usually mp3tag is too slow. In APE files is less than a second, in most of FLAC files I have to wait about 20-30 seconds per file. ¿Is it normal?.
In earlier versions of mp3tag there is not this problem.
FLAC describes an audio format.
APE is a tag format.
FLAC files usually have the seize of several MB.
A tag has the size of some KB (factor 1000 smaller than the whole file). So if you modify the tag, not a lot has to be written.
Unless ... you add so much data (very likely when adding pictures) that the padding does not suffice. Then the whole files has to be rewritten.
It think I have to apologize for my ignorance in that field.
Now the post by pepeillo001 makes more sense (to me).
So please ignore most of what I have written in post #2