Use tools to check if files are truly "unidentified developers" if they are downloaded from the internet, as Apple devices sometimes block them by default.
If an MP4 file is corrupted, you can try re-encoding it using tools like Adobe Media Encoder to resolve issues with red screen frames or playback failures. 56 mp4
If your default player (QuickTime, Windows Media Player) won't play an MP4, try VLC Media Player , which supports nearly all video formats. Use tools to check if files are truly