Often translates to "dog" in Japanese. This could indicate the video features a dog or is related to a Japanese project.
An MP4 (MPEG-4 Part 14) is a digital multimedia container used to store video, audio, subtitles, and images. inu_un_8.mp4
If you downloaded this from an unknown source, run it through a scanner like VirusTotal before opening it. Often translates to "dog" in Japanese