ITunes 10.7: Does listening to songs change their mp3-files

backupitunesmp3

I use iTunes to listen to music and I use Wuala to backup my mp3-files. Before recent versions of iTunes, I never had any problem with that.
But with more recent versions (I don't know when it started, but the problem definitely occurs in the current version 10.7), there is a problem: Whenever I listen so a song on iTunes, Wuala makes an update of the backup, i.e. the songs that i listened to are uploaded anew. This means that Wuala thinks that the file has been changed. I find it really annoying because this uses CPU and bandwith when I listen to music. I want to solve this problem.

My question: Is it true that iTunes, in more recent versions, changes the mp3-file when listening to a song, or is the problem caused by newer versions of Wuala?

EDIT:
Thanks, Dave K. Comparing checksums is a good idea. I've just done the same: I checked the checksums before and after playing a few tracks, and none of the checksums changed. However, Wuala still uploads played tracks. On this screenshot, one can see that Wuala uploads tracks the checksum of which has not changed:

Wuala upload

Thus, Wuala updates files which haven't changed. What else could be the reason why the tracks are uploaded? I noticed that iTunes opens the mp3-files with write access, as one can see from the fact that the information in Finder shows identical times for "modified" and "last opened" (is this a correct conclusion?):

iTunes opens with write access

Could that be the reason why Wuala uploads the files? Where is the information stored that a file has been last modified at a certain time? (not in the file, since the checksum doesn't change)

Best Answer

My Setup: Crashplan, OS X 10.8.2, iTunes 10.7 (21)

I am unable to replicate the same issue on my system, and haven't noticed any excess changes or uploads to crashplan on my filesystem after playing music. To be sure it wasn't happening in the background, I ran a checksum on one of my audio files, played the complete song in iTunes, and re-ran the checksum. If something in the file itself had changed, the checksum would be different.

Here are the results:

Big-iMac:Abbey Road dave$ openssl sha1 17\ Her\ Majesty.m4a 
SHA1(17 Her Majesty.m4a)= 3aea5150d7b1d21846b6502bac7ccacca44ff0fa
Big-iMac:Abbey Road dave$ openssl sha1 17\ Her\ Majesty.m4a 
SHA1(17 Her Majesty.m4a)= 3aea5150d7b1d21846b6502bac7ccacca44ff0fa

As you can see, the checksum matches the second time after playing the song through iTunes. Most of my collection is ripped into ALAC (m4a), so I thought I'd test a standard mp3 file as well:

Big-iMac:One More Night in New York City dave$ openssl sha1 2-21\ The\ End.mp3 
SHA1(2-21 The End.mp3)= a223d6fb542bee5191794d0a74f971da19fb9afc
Big-iMac:One More Night in New York City dave$ openssl sha1 2-21\ The\ End.mp3 
SHA1(2-21 The End.mp3)= a223d6fb542bee5191794d0a74f971da19fb9afc

This too produced the same checksum before and after playing the song in iTunes. All of the metadata about your library (play count, etc.) is stored in the iTunes Music Library.xml file, not in the mp3 itself so I wouldn't expect individual songs to change. However, it's quite possible that the iTunes Music Library file will need to be re-uploaded since it changes frequently.

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