When I set up my Rune Audio system I copied the .mp3 and .m4a files from my iTunes library to /mnt/MPD/SD. I then found that it took about half a second for Rune Audio to list the contents of an album (this is a pi 3B), the reason being that it is programmed to do the following until it succeeds in finding album art:
- 1. Search for an album art file in the same directory as the music files. (It looks for any of the following: cover.jpg, cover.png, folder.jpg, folder.png, front.jpg, front.png.)
2. See if there is any album art in one of the music files. This uses kid3-cli which takes about 300 ms to run, even if there is no album art in the specified music file.
3. Query ws.audioscrobbler.com to look for album art.
So I figured that based on the above, the best way to speed this up would be to copy across album art files for the albums. I found that on my iTunes system (Windows), a lot of the directories contained a hidden system file called Folder.jpg, which indeed contains artwork for the album in question. Because it's a hidden system file, by default it's not visible in File Explorer or if you run 'dir' at a command prompt, but it is listed if you run 'dir /a'. You can remove the 'hidden' and 'system' attributes from the files by running 'attrib -s -h <path>\Album.jpg', and then copy them across to /mnt/MPD/SD. After that, I found that listing an album took more like 150 ms (and artwork is shown for many more of my albums), so I was delighted with the improvement.