This script will embed artwork that has already been downloaded (via the iTunes "Get Album Artwork" command) into the files of the selected tracks.
Also see Re-Embed Artwork.
NOTE: For best results, use with an album's worth of tracks--or so--at a time. iTunes may be obliged to perform a number of background tasks when applying image data and may prevent the script from proceeding if a large amount of data is involved.
Note: (August 2014) Not sure what the issue is but results are inconsistent with modern versions of iTunes.
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Exports and then re-imports selected tracks' artwork
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Set the Plays of selected tracks.
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Displays files in iTunes Media folder not in iTunes track library
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Finds and displays any empty folders in the iTunes Media folder
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Move selected playlists to a new or existing folder
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Perform tasks on a batch of playlists; rename, delete, duplicate, merge, more