LOS ANGELES: If you were going to reinvent MTV for a mobile generation, you'd probably come up with something like YouTube Music. It's a video-first music service that also plays in the background like you'd expect a music app to do. That sets it apart from other music apps out there, many of which give you a choice of videos or songs, but not interchangeably.

But while YouTube Music offers a lot of interesting features, most of them require a subscription to the new YouTube Red service, which will set you back $10 a month — $13 if you sign up through YouTube's iPhone app. Without Red, YouTube Music will play ads similar to what you see on YouTube proper, and several other functions won't work at all. YouTube is offering new users a 14-day free trial to Red, but to continue commercial free, you'll need to pony up.

YouTube Music is first and foremost a music-video app, albeit one that doesn't forget that most people will be using it on their phones. For those times you'd rather just listen instead of watching, you can hit a toggle that switches the app to audio-only mode, which turns off the video playback and swaps in a still image. You can even turn off the screen and keep listening while you do something else.

But here's the first gotcha: Audio-only mode only works for paid subscribers. I also found the audio-only toggle worked far better on a Samsung Galaxy Note 4 than on an iPhone 5, where it introduced a jarring pause.

You can similarly shrink the video to a little strip at the bottom of the app, which keeps it playing in a cropped format while you look for the next video. The app will even keep playing if you switch to other tasks, like checking email — although again only if you've paid up for Red.

There are some curious omissions. For instance, there's no easy way to create a playlist to queue up a bunch of videos in a row. The app does offer "song stations," which queue up videos from artists related to the one you're on. You can toggle the range of the resulting mix with options like "less variety," ''more variety" or "balanced." I started a station starting with Passenger's "Let Her Go" and so far I'm pretty happy with the "balanced" playlist it created, which included "Counting Stars" from OneRepublic and "Burn" by Ellie Goulding.

You can also play all of the videos you've thumbs-upped, which turns that grouping into a crude sort of playlist.

YouTube Music is far less cluttered than competing services like Apple Music, which has more lists and tabs than you'll know what to do with. YouTube Music keeps the tabs to three — home, hot (trending videos), and thumbs up (your favorites).

Home offers recommended videos, and it's easy to find something playable. Your mileage may vary with the "hot" tab; it didn't do much for me, although I'm usually a bit out of sync with the mainstream.

Finally, there's one more fun feature, which is called "offline mixtape." It automatically saves 20 audio-only songs for you based on your tastes, for when you know you're going to get spotty reception. I wish it saved the videos instead of just the audio, but this will keep the tunes turning in a pinch. Alas, offline mixtapes are disabled in the ad-supported version of YouTube Music.

The app makes Google's $10-a-month music subscription a lot more attractive. Paying up not only unlocks features in YouTube Music itself, it also gets you ad-free playback on the main YouTube app, access to Google Play Music, and, down the road, some original material from YouTube stars.