I imagine it's the Tag Sources script author that controls whether or not cover art is fetched when using the Tag Sources feature, but I think it could be useful for the user to be able to override this behavior.
The reason being is this: when I search for an album, I'm first presented with a list of matches (which is usually quick being only text), but when choosing an album by pressing Next, the speed at which total album information is downloaded can vary from one to the other, and I believe this is because of the varying cover art filesizes.
Would it be possible for the user to override this, thus speeding up tagging on slower connections? Maybe there are other related reasons for the slowdown, but I'm thinking it's my connection speed.
Ideally, one could re-enable fetching cover art (via the cover art context menu / a checkbox) right on the fetched album information page ("Adjust tag information"), and then Mp3tag would request a re-fetch, this time with cover art.
About how many seconds are we talking?
Anyway: as the web source scripts are plain text files, you can edit them yourself and remove any lines that deal with the cover.
You could save a copy of the original source so that you can select whether you want to have the cover or not.
And this would also be a good test environment to see if it is really the cover or perhaps still the complexity of the web source itself.
You're right, it possible it's the complexity of the script - It's actually an edit I did some time ago of one of the default MusicBrainz ones I believe. It just feels like it noticeably hangs at times for longer than it should. Other times it feels snappy in comparison. Regardless if it's the script's complexity or not, it would be nice to override downloading, say a 5MB image, that will only ever be displayed as a tiny UI preview when it's not desired to be written/saved. Having to edit a web source script is an option for me, but not something the average user with a slow connection may be comfortable doing. I think it's a reasonable option to be exposed to the user.
A 15 track album:
0.5s without cover art
2s with cover art (13 KB)
4s with cover art (1 MB)
4s with cover art (2 MB)
5–10s with cover art (5 MB)
15–30s with cover art (13 MB), window hangs and grays-out, eventually recovers.
These were fairly consistent results. The time taken only varying quite a bit for the larger images.
I'd have to look inside the script to get a better idea of what's going on, but the only pattern I'm seeing on the surface is larger cover art filesizes causing slowdowns. There could be other reasons, but I don't have the time right now to delve any deeper.
I've been thinking about something similar lately. I download a lot of covers, as I tag & add covers to all of my MP3 files (literally 25,000+). There is no way to tell in advance if a cover exists, or how large it is (I use MusicBrainz, but this applies to all sources). Sometimes I click on a match and no cover comes back, and other times, it's almost instant with a cover, and other times it sits for 5-10-20-30 seconds while it downloads a huge cover, sometimes 20MB in size.
It would be helpful if we had some choices here. Maybe a checkbox that says "Don't dl if over 'X' MB". Or something that pre-fetches the size only, and shows you what it is before you dl.
I don't know how it works, so I can't really offer solutions. I only know this is a minor yet ongoing annoyance.
Before any size data can be displayed, the cover has to be touched somehow, and sometimes the preview is also useful.
If you do not want to download the cover into the files, then please see the options in the "Utils" button menu where you can set whether a cover should be embedded in the files or saved in the files system or both or nothing at all.
I don't know if this will actually speedup things.
I assume the Utils button is the right-click menu of the cover art? I already have both options disabled so the cover art isn't saved anywhere other than %temp%\Mp3tag v3.04a, which to me is what I'd like to avoid.
In the web source search result dialogue where you see the list of titles, the cover, artist, album and where you can move the files to their correct position in the titles list, there you find a button called "Utils" at the bottom left.
This button features a little menu with functions and options.
That is what I meant.
I don't have any automatic downloading into files or embedding enabled. I always look at the image first, and the size, before I decide what to do. My issue is the script downloads the image before I can preview it (which makes sense). I wonder if there is a way to determine the size BEFORE it downloads it. And if over a certain size, offer me options--preview it anyway, skip it, etc. Those 20MB images are a PITA.