How do Nautilus album art thumbnails work?

Question

There's something for which I've been searching an answer for a while now, but to no avail, and it's strange to me, as it seems like a thing that people would talk about: one of those nice little nonsense that enhance the computing experience a little bit.

Anyway. I have a fair music collection. I save all the songs as ogg files. All is fine, and I can listen to the files, but there's something weird with the files in Nautilus: some have icons displaying their album art, while others don't, and I just can't understand WHY.

I read on this site today that it's a matter of embedding the album art to the file, but that's not true, as I embedded the album art to the files I wanted several times, to no avail. Furthermore, removing an embedded album art from a file didn't have any effect on those that ARE displaying the icons.

So my question is: How does it work? Where does Nautilus (or Ubuntu, I don't know) get the picture from? How do I edit it?

Solution

I believe it does in fact use the tags embedded in the file, which are usually called id3 tags, at least for MP3. I think ogg files read id3 tags, but may not read id3v2 tags (version 2). Some software writes one or the other, or sometimes both.

I've noticed that it takes a while for Nautilus to display the album art once the folder is first opened, but then it remembers them. I'm pretty sure it stores the images in ~/.thumbhnails/normal, but this directory can be very big, and opening it is a chore.

I've heard of a program called "cover thumbnailer" that makes nautilus work better; I haven't really tried it out myself, though.

Comments

[Amir Adar]

I got it! I renamed the old "normal" folder, and it re-read the files and worked with the new embedded images. I probably won't install "cover thumbnailer", since it's not in the default repositories, and I'm trying to be cautious about it. Still, it's a little bit of a clumsy way to change the pictures. I know I can just set custom icons, but I can't do it to a group of images and it just comes out smaller and is a lot of work. Thank you for your answer, it really helped!

[Amir Adar]

However... after checking several folders, it seems that not all of the files display any pictures (only the default music icon), even though I've embedded pictures into them just like I did with the rest. Why is that? Thanks again for putting me in the right direction. :)

[Amir Adar]

Another note (and I'm sorry if I'm being annoying now) is that when I copy and paste the files it shows the icon as it should, but when I rename the files from "* (copy).ogg" back to "*.ogg", leave the folder and come back in, the icon is gone and is replaced again with the default music icon. So it seems to be holding some grudge against the files' names.

[Deepak Verma]

Remember, it takes a while to finally display the thumbnail if it's not in the directory; how long probably depends on how many files there are to search. Also, remember the pictures are stored in each file, not by album or directory, so some files may not have the embedded album art. Also, I'm guessing that the thumbnail filename is somehow keyed to the file's UUID, or something similar, so renaming may lose this connection. This is all educated guesses, by the way.

[Amir Adar]

It takes a while, but it shows that it's loading a thumbnail, if it does indeed load one. Since it doesn't, it simply presents the default thumbnail for the filetype. I embedded the album art manually to each file in Easytag, so I know all the files are embedded. I don't really know what a UUID is, but I think I understand what you are saying. Still, the problem is that the file with the original name does not load a thumbnail, but a copy named "filename (copy).ogg" does load a thumbnail of the embedded image. Renaming the copy back to the original name removes the thumbnail.

[Amir Adar]

Ah, now I got it. I removed the old "normal", "large" and "fail" folders from ~/thumbnails, and it now displays all the right icons. Apparently, according to the thumbnails folder, once there's an icon for a file, there's no turning back, until you wipe it out and remake it. Thanks again for all your help!

[Amir Adar]

Yes, that's what I did, but for a long time it didn't work, and that was because the hidden icons folder already had icons specified for the filenames and it didn't agree to switch them. Deleting the icons folder solved that problem, as it recreated itself and added the right icons.

[Amir Adar]

Yes, that seems similar, however, the comment in the end says that Nautilus is unable to read the tags, while I successfully made it read them. I'll post a comment of my woraround, and hopefully it will be of use.

[Amr Ibrahim]

Unfortunately, your workaround didn't work. There are still some files which didn't show their thumbnails. Just like before; randomly, some of them did and the others didn't.

[Amir Adar]

I see. I don't know what this is about, then. Hope you manage to find a solution.

[Volker Siegel]

That's exactly how it works for images and videos - where it makes sense to use a size limit. It makes no sense for reading headers of mp3 files, but I presume it is applied here too.