Tags in Library file v. Song File

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Level 1

86 points

Tags in Library file v. Song File

Anyone know what tags actually become part of the song file and what tags exist only as a function of the library file? For example...

If I import a folder (not copying song to lib), change info about the file in iTunes, is the changed information written to the file or stored only in iTunes itself?

I know, for example, that I can add artist/album tags to .wav files, but .wav files don't support tagging. So, I am presuming that if I import those same songs into iTunes running on a different machine with access to the same folders, I get nothing and have to reconstruct the album/artist info.

But, mp3, aac, Apple Lossless support tagging in the file, so, if I change the info for a .aac, will that information remain associated with the file even if I import it into a different iteration of iTunes?

Are there particular fields that will/will not be written to the original file? Are particular formats better/worse? Any way of forcing iTunes to write the tags to the files if it doesn't automatically?

I'd try some experimentation, but I'm stuck at the wrong machine...

Posted on Oct 28, 2005 4:30 PM

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Answer 1

Buegie

Level 6

13,331 points

Oct 28, 2005 4:36 PM in response to Eric DeSilva

For M4A/MP3 files...

These are in the iTunes Library only:
-- Playlists
-- Ratings
-- Play Count
-- Last Played
-- Date Added
-- Date Modified
-- Equalizer
-- Volume Adjustment

These are stored in the music file itself:
-- Comments
-- Genre
-- Grouping
-- Volume Adjustment (this is a special iTunes only tag in the file, it's non-standard)
-- Composer
-- Bit Rate (not a tag, but inherent to the file itself)
-- BPM
-- Kind (not a tag, but inherent to the file itself)
-- Album Art ( only stored in the file, this doesn't get copied to the iTunes library files)

Based on info from Otto42 and some of my own inspection.

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Answer 2

Eric DeSilva Author

Level 1

86 points

Oct 31, 2005 8:30 AM in response to Buegie

Thanks, seems like it working with my ALAC files, so that solves my problem.

Given that there are library specific tags that iT recognizes, I wonder why they couldn't have implemented album art for WAV files just as a library thing. Heck, that is the way artist/album are dealt with...

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Answer 3

MacMuse

Level 7

20,796 points

Oct 31, 2005 11:47 AM in response to Eric DeSilva

They probably made a concious decsion to not store Album art in the iTunes library file to avoid growing that critical file to excessive size.

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Answer 4

Eric DeSilva Author

Level 1

86 points

Oct 31, 2005 12:16 PM in response to MacMuse

I guess I was thinking link to art file, versus actual art in the library. I mean, after all, the lib only really contains a pointer to the song files...

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Answer 5

MacMuse

Level 7

20,796 points

Oct 31, 2005 12:28 PM in response to Eric DeSilva

but itunes does not use "art files". For iTunes, artwork is stored in the music file as an ID3 tag.

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Answer 6

Eric DeSilva Author

Level 1

86 points

Oct 31, 2005 12:35 PM in response to MacMuse

I guess that was sort of my point... Artist/album information is stored in the music file as an ID3 tag as well, but the developers made the choice to allow an XML tag in the library file with that information in it for WAV files that is library file-specific. Doesn't seem like it would be that much of stretch to do the same thing with album art--create an XML reference to a jpg or gif. The bottom line, I guess, is that there aren't too many people using wav files, so it probably isn't worth even minimal development effort.

Frankly, just this weekend, I converted my whole WAV lib over to ALAC anyway... Just idle curiousity at this point.

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Answer 7

MacMuse

Level 7

20,796 points

Oct 31, 2005 3:06 PM in response to Eric DeSilva

Yeah, I'm a little bored on weekends now that the World Series is over, too. 😀

Technically, it is quite easy to incorporate the artwork into the library. But the trade-off is performance in iTunes while reading the library. For example:
* turn off artwork display in iTunes (ctrl-g)
* select Library
* select first song in listing
* press & hold the down arrow (or even "page down" key if you have a large library)

iTunes shouldn't even blink - the list should just fly by on the screen with little or no hesitation. That's because it's mearly reading the ITL library file and not touching any of the real music files. If iTunes had to process image "files" embedded in the library file, the size would become unworkable and you would lose the speedy scroll and search functions.

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Answer 8

Eric DeSilva Author

Level 1

86 points

Oct 31, 2005 4:00 PM in response to MacMuse

Guess I assumed that it was reading the lib file once per session, even if it rewrote it on occasion...

I'm not sure I'd say anything in iT "flies" by... My library is about 14K of ALACs and the same number of AACs (the downconverting on the fly for the iPod was tooooo slow). What is killing me now is the update time for cover art--takes a good 3+ minutes to update an album with Get Info, which is horrendous (altho' that is both AAC and ALAC copies). Granted, the music files are coming off a terastation 1TB NAS with software RAID5, but there isn't any other network loading...

Actually, the conversion wasn't too bad. I selected all the WAVs, set up a new library on the fresh drive, and told it to convert. Took mebbe 36 hours. Wasn't nearly as bad as converting the WAV files to AAC 128 kb/s copies, which took over 100 hrs.

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