Concept for providing cover art for single tracks

[Tobias Leupold]

Am Sonntag, 18. September 2022, 10:08:01 CEST schrieb Tobias Leupold:
> Dear Elisa devs,
> 
> currently, there seems to be no way to provide CD cover images for single
> tracks. In FileScanner::searchForCoverFile, there is a per-folder search for
> all kinds of images that could be the cover art -- for that album. But a
> collection of single tracks normally don't live in a per-album folder
> structure, so this won't work well for single tracks (at least for my
> collection structure).
> 
> Lately, I worried about how one could solve this.
> 
> Back in Amarok days, one could add cover images for all tracks. Amarok
> calculated some MD5 ID from the lower-case file name or such IIRC and
> created an Amarok-specific cover archive to be used whilst playing songs.
> This worked fine, but the problem was that a lot of work had to be done to
> always see covers, but the result was application-specific, with no easy
> way to reuse it (e.g. in some script). Also, those IDs were
> filename-agnostic IIRC.
> 
> I think there would be a quite straightforward solution for providing cover
> art for all songs. What do you think of the following approach?
> 
>  - We define a folder containing all cover art. This would be typically some
> folder inside the collection root (of course configurable by the user).
> 
>  - We read, if present, the MusicBrainz album ID of the respective song
> 
>  - If there's a MusicBrainz album ID, we check if the song's folder contains
> some cover art as it's done now. And if not, we check if the cover art
> folder contains a file named [id].jpg/png
> 
> I use such an approach to generate normalized songs to be used in my car's
> radio: I decode the song I want to add, calculate it's EBU R 128 loudness
> using ffmpeg, apply it and re-encode it to a format my car will play, with
> the normalized loudness applied (as of course stuff like ReplayGain or EBU
> R 128 tags aren't considered). And: I embed the cover art for that album,
> which I find using it's MusicBrainz album ID.
> 
> This is quite easy: I do this with a small Python script using Mutagen,
> which exposes the MusicBrainz album ID as "TXXX:MusicBrainz Album Id" or
> "musicbrainz_albumid" (depending on the file type) if one uses the (most
> convenient) mutagen.File extractor. And thus, I know which file to embed.
> 
> This way, multiple songs can link to one cover image, no matter if it's a
> whole album or a single song. Also, the file name can be easily found, and
> it is static, even if the album name would be changed (corrected). Also,
> being an UUID, we won't have to worry about collisions. And the file's path
> doesn't matter. And this is reusable, not application-specific.
> 
> Well, I thought this would almost be trivial to implement, so I tried to do
> it and file a MR. But sadly, there are some problems for me :-(
> 
> I must admit that I don't find my way too well in Elisa's sources. But as
> far as I could grasp it, KFileMetaData is used to extract the metadata that
> is put in the SQLite database. Now, KFileMetaData::Property doesn't list
> MusicBrainz stuff, so I think a custom extractor exposing it would be
> necessary to be implemented. The rest would really be easy I think. Just
> invoke
> FileScanner::searchForCoverFile with not only the file name, but also the
> MusicBrainz album ID and do one additional lookup.
> 
> Anyway ... before I become too obsessed with this idea, I wanted to ask what
> you think about this approach, and if this would be something beneficial
> for Elisa.
> 
> Thanks for all feedback!
> 
> Cheers, Tobias

PS: Perspectively, using this approach, one could also add a quite simple 
interface to retrieve cover images using the coverartarchive.org API. It's as 
simple as requesting https://coverartarchive.org/release/<the album id>/, 
parse the JSON answer you get (if it's present) and download what you want.

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Cheers, Tobias