Save Bandwidth When Playing YouTube Music Videos

I've checked to see what happens when you play a YouTube music video in the background when using the YouTube app for Android, while YouTube Music Key is enabled (it's bundled with the Play Music All Access subscription). I played U2's Beautiful Day on my Nexus 5 and opened the app data usage section to see how much data is used by the YouTube app.

When playing the video in the background, the YouTube app used about 4MB.

When playing the same video in the foreground, the YouTube app used about 24MB.

By default, YouTube selected the highest video quality that was available for this video: 480p.

This means that you can save bandwidth by playing music videos in the background. YouTube uses separate chunked streams for audio and video, so it can download only audio files when playing videos in the background.