Why can't you use the stock music app?
I use iZip Pro for playing music sometimes. Another is Documents by Readdle. I think both play offline, if they're downloaded offline in the stock music app. If you want something fancy, TunesFlow is nice.
Why did you start 2 threads on this?
You can download videos from Twitter with this app. I just checked to be sure. It's tricky though.
Video Saver Pro - Video Player for Cloud Platform by Nguyen T Nam Giang