My TV box started to develop HDMI output problems caused by loose connection. So I explored alternatives like install Kodi on Deepin v20.9. Kodi in Deepin doesn't work as well as the TV box Android version. It's not able to play all the files the Android version could. So then I'm back to using the built in Deepin v20.9 movie player.
BUT there are various problems:
Deepin movie player doesn't automatically play the soundtrack file. When using a free online tool to download 4K videos from YT, you only get the video not the sound. I fixed this problem by downloading the soundtrack separately as an MP3 file, then rename the file to be the same as the video (before the file extension). Kodi knew right away to play the soundtrack file, but in Deepin movie player, even the option to load soundtrack is greyed out!
4K 60fps videos. It seems Deepin is not smart enough to play it like 4K 30fps (skipping every other frame). As a result on a 6th gen Intel CPU, 4K 60fps videos look like they're played in slow motion at half the speed of regular 4K 24fps videos.
中文 
My TV box started to develop HDMI output problems caused by loose connection. So I explored alternatives like install Kodi on Deepin v20.9. Kodi in Deepin doesn't work as well as the TV box Android version. It's not able to play all the files the Android version could. So then I'm back to using the built in Deepin v20.9 movie player.
BUT there are various problems: