With a single tap, the Twitter Audio Card lets you discover and listen to audio directly in your timeline on both iOS and Android devices. Throughout your listening experience, you can dock the Audio Card and keep listening as you continue to browse inside the Twitter app. We’re launching this new audio card in partnership with third-party streaming services. The first partner for streaming on Twitter is SoundCloud.
Twitter’s dedicated music app didn’t take off, but this sounds like a cool idea. Tried it and it works very well. Unfortunately, it doesn't seem to work if the Twitter app is in a background mode. Hopefully, that will change in the future versions.