This usually happens when Mirada doesn't have the codec necessary to play the file.
You can change the codec used in playing videos. To do this:
Main menu - Media - Open using - Library manager...
Choose a different library for your file type
Try to play the video file
If changing libraries didn't help, contact our Support: https://cerebrohq.com/en/support/
Please provide us with an example of your video file, or codec information.
We will add support of the required codec to Mirada as soon as possible.