Music files from iTunes are usually saved in MPEG-4 format, which is unable to be used in Scratch. Here's how to convert that file, and use it in your Scratch programming.

.:Preparation:.
You need to download THIS program to start.

Launch iTunes now.

.:Procedure:.

1) Go to iTunes→Music→Edit→Preferences.
2) You will see a button saying "Import Settings". Click it.
3) There will be a drop down menu named "Import Using". Select "mp3 encoder.
4) Drag and drop the song onto your desktop.
5) Right-click, and select "Convert with Switch Sound File Converter".
6) Click convert, and your song should come out in the .mp3 format!
7) REMEMBER to save it to your desktop.

.:Puttin' it in Scratch:.

1) Go to the Sounds tab, and then click "Import".
2) Find your Desktop or wherever you saved it too, it should be there.

Voila! You now have a song in Scratch!

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Hope this helped!