There's a reason this Windows 7 release is a Beta. The versions of Windows Media Center and Windows Media Player that shipped with the OS have a nasty bug that may damage your MP3 files. By default, Windows Media Player 12 enables a feature that auto fills-in missing metadata on your imported music files, which includes large album art. But filling in this metadata on files that already have large headers will permanently cut away a few seconds of audio from the beginning of the track. Microsoft offers a hotfix on this page: http://support.microsoft.com/kb/961367 in addition to a workaround if you don't want to install the fix:
If you do not apply this update, the most effective workaround is to set the properties of all MP3 files to read-only on local hard disks, removable drives, and network shares that can be accessed by Windows 7 Beta computers. To do this, follow these steps:
1. In Windows Explorer, select and right-click your MP3 files, and then click Properties.
2. On the General tab, click to select the Read-only check box.
3. We recommend that you back up all the MP3 files before you use Windows Media Player or Windows Media Center.
A simpler but less complete workaround is to disable metadata automatic updates in Windows Media Player by setting the Windows Media Player options. To do this, follow these steps:
1. On the Tools menu, click Options.
2. On the Library tab, click to clear the Retrieve additional information from the Internet check box and the Maintain my star ratings as global ratings in files check box.
3. Click OK.
A possible solution to the MP3 file corruption issue
If some of your MP3 files have already been affected, you might be able to restore the corrupted MP3 files to their pre-edit status. To do this, follow these steps:
1. In Windows Explorer, right-click a corrupted MP3 file, and then click Properties.
2. On the Previous Version tab, select an earlier version in the File Versions list, and then click Restore. If multiple edits were performed, you may have to revert to the oldest version that is available.
