Because ".mp4" is a generic video file extension and "g_159" appears to be a specific filename, it is likely one of the following:
Knowing where you saw it or what it's supposed to show will help me track down the specific details for you. g_159.mp4
To help me find a relevant review, could you provide a bit more ? For example: Where did you encounter the filename? Is it related to a specific game, creator, or subreddit ? What is the subject matter of the video? Because "