May 08, 2017 This article explains how to format a device or disk (e.g. USB flash drive, external hard drive) into the proper format that is accessible by both Mac and Windows computers: Disk Utility 12.x: Format a disk for Windows computers. In regards to your second question, check out this article: If QuickTime Player can‘t open an audio or video file. Jul 15, 2009 Format a drive for Mac OS X and Windows. If you move a hard drive between the two operating systems, here's what you need to know.
Hello, gaminhk!
Thank you for reaching out and using the Apple Support Communities. We see from your post that your seeking a way to make your MP4 videos viewable on both Mac and Windows PCs. Having that shared compatibility between both operating systems is very important, especially when you want to share to them with others.
In this situation, the best way to ensure that both a Mac and a Windows PC can access the videos from the same external device is to make sure the device is in the correct disk format. This article explains how to format a device or disk (e.g. USB flash drive, external hard drive) into the proper format that is accessible by both Mac and Windows computers: Disk Utility 12.x: Format a disk for Windows computers
In regards to your second question, check out this article: If QuickTime Player can‘t open an audio or video file