Comment 11 for bug 135956

Mathias and I were discussing what it would take for us to support cue sheets. I'm also checking the behaviour of foobar2000, which supports cuefiles and whose tagger is _good_. The following are some of the ideas/findings:

- We can represent the URI of each track as file:///path.cue#01 (or #1; doesn't matter I guess). This means that we have to read the cuefile for each track played, but I don't think it's a big deal.

- Alternatively, we can also represent it as file:///path.ogg#100.0-200.0 (file, start, end). The problem with this is we lose the cue filename (required for tagging), so it has to be either encoded in the URI or stored somewhere else in the metadata.

- The cuesheet spec only supports some formats from the stone age (including mp3). fb2k simply specifies WAVE for Ogg/Vorbis or other formats.

- At album level, fb2k supports PERFORMER "Artist", TITLE "Album", REM DATE 2000, REM GENRE Genre, REM COMMENT Comment, and perhaps others. It also adds tags specified in the original music file, although preferring tags from the cuefile.

- At track level, fb2k supports PERFORMER "Artist", TITLE "Title", and REM DATE 2000. Perhaps also songwriter, though I didn't try.

- Technically, with the REM syntax we can support anything. fb2k does not do this; some tags will simply not get written, and the album-only tags can't be attributed to individual tracks (which makes sense for genre and album, but not for comment).

- In general, handling differences between album- and track-level tags will be somewhat tricky.

- There can be an album artist and (for each track) a track artist specified. fb2k is really smart when it comes to handling various album/track artist situations (for example, If all track artists are the same and there are no album artists specified, it will be written it to the cuefile as the album artist instead), but we can get away with a simple implementation first.

- We have to handle the case when the user tries to modify an album-level tag (e.g. album artist) on 1 track only. Do we change the album artist from all tracks in the album? Do we refuse to make the change unless all tracks are selected? fb2k is somewhat buggy in this; it will remove all instances of that tag instead.