So you've got a bunch of video files on your phone or tablet (all legally acquired I'm sure), but they use a variety of codecs. One of the more popular ways to play them is MX Player, which has a few hundred million downloads in the Play Store—no big deal. Now you can get the latest tweaks and features in MX Player via a Play Store beta.
This is a standard Play Store beta and does not require you to join a Google+ community first (remember, Google removed that requirement). There are beta channels for the free ad-supported and pro versions. Just head to the opt-in page and you're all set. Your devices will update to the beta, and you can choose to leave the program at any time by visiting the opt-in link again.
MX Player has a ton of features already including gesture control, multi-core software decoding, hardware acceleration, and subtitles. Most of the updates these days are bug fixes. Maybe the beta channel will be used to test something more substantial, but there's only one way to find out.