I bought a new dashcam. It generates .mp4 files. I tried to play them back with my new Roku media player, and it says invalid format. (They will play with Windo

I bought a new dashcam. It generates .mp4 files. I tried to play them back with my new Roku media player, and it says invalid format. (They will play with Windows media player.) Grump grump grumpity grump. Same experience with every dashcam I've bought over the years.