Sorry to disappoint… but the USB ports on a DIRECTV receiver won’t let you play videos. In fact, they’re not good for much of anything. You can connect up an over-the-air tuner, or add a network adapter if you need one, or charge your phone. Truthfully, not a whole lot else.
The best answer that’s been given for why DIRECTV receivers have USB ports is that they’re used during the pre-release testing process and then left there because the hardware would need to be recertified if it changed. So they’re really sort of leftover bits kind of like your appendix. Definitely not something you’d ever use for any reason like streaming.
There was a time that DIRECTV tried its hand at letting you stream from network sources, but the truth is that it never worked very well, and at this point pretty much any streaming device no matter how old is going to do a better job. As far as I know that capability has been gone from DIRECTV equipment for a long time; I don’t know anyone who missed it when it finally disappeared.