Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
Try logging out of your Google account on the tablet.
Then clear cached memory.
Then restart the tablet.
Then see if, after logging in to your Google account once more, you can get video.
If that does not get the problem fixed, then please let me know whether the sound from Google Play is getting through and can be heard.
And also let me know what app you are playing the Google Play content in/from. Thanks.