Why QuickTime Can't Play MP4 or MOV files?
The Core of The Problem
As we know, extension is the container format of a video/audio file. QuickTime first check the extension of the file and then automatically select a codec to encode the file. If the codec of your MP4 or MOV files is not supported by QuickTime, it still can’t read the file even if the extension is recognizable to QuickTime. The following part explains how to tackle this problem in an easy way.
Convert Video to QuickTime Format on Mac OS X
Step 1, Download and install QuickTime video converter
You can download it for free here:
To install it, simply mount the .dmg archive by double-clicking it, and copy the application to your applications folder (or wherever you want).
Step 2, Load video filesClick the "Add Files" button to add video files to the program. This QuickTime video converter for Mac supports drag and dropping. It also supports batch conversion, so you can import and convert several multimedia files at a time.

Step 3, Select output format
Use the “format” on the bottom of the window to control the output format. Click on the toggle to the right of the "Format" label to expand the panel. Select "MOV - QuickTime (.mov)" as the output format.

Step 4, Change QuickTime Video and audio Settings

Click on the “Setting” button to expand “Setting” panel.
You can change the Resolution, Encoder, Bit rate and Frame rate of the QuickTime video and Sample Rate, Channels, Encoder and Bit Rate of the QuickTime Audio. The size of the QuickTime file depends a lot on these settings.
Step 5, Select output directory
Expand the "Output" panel. Use the "Browse" button to select an output directory.
Step 6, Click “Convert” to convert Video to QuickTime files on Mac.
