My son sent me a video of him playing guitar and singing. He said it plays on his phone (Android) but I can't hear it on my phone (Android), although I can hear other videos that have been recorded.
Welcome to Android Central! How did he send it -- via text? Tell him to upload his video to his Google Photos account, and then share the video with you through Google Photos. That's a good way to make sure the video comes through in its original form, and not highly compressed (which is necessary if sent via text).