QuickTime, which has the powerful feature of handling various formats of digital video, picture, sound, panoramic images, and interactivity, is becoming a popular video player for both Windows and Mac user. However, Even with such a powerfully media player, you still can encounter a case that you are trying to play a common file format like MP4 but end up in "fail to open" situation in QuickTime. We know that the MPEG-4 file format specification was based on the QuickTime format, so that QuickTime does support MP4 as one of the input formats. But why we still encounter the situation that QuickTime won't play MP4 files sometimes?

Part 1. Why QuickTime Won't Play MP4?

MP4 is a very complex container which can contain video and audio components encoded with different types (codecs). However, QuickTime can only support MPEG-4 (.mp4, .m4v), That is, if the MP4 video contains QuickTime unsupported audio or video codecs, QuickTime will refuse to play this kind of MP4 files.

Part 2. How to Solve QuickTime Won't Play MP4 Issue Easily and Freely

Usually, there are two methods to solve QuickTime won't play MOV video files:

Method 1: Download MP4 Codec

Install the corresponding video or audio codec needed for playback the MP4 video on QuickTime. In this method, you must first check the inspector or info windows to see what codec is contained within the MP4 videos, then download and install this codec.

Method 2: Convert QuickTime unsupported MP4 to QuickTime compatible format with video converter.

To solve this issue easily and freely, this is the strongly recommended solution. With a powerful video converter, you can convert the unsupported MP4 to any compatible format that QuickTime supported,  VideoSolo Free Video Converter is a free and powerful converter that I want to recommend.

This wonderful converter is also an all-in-one video converter, editor, and player, with which, you can convert files among more than 300 formats, optimize your video and movie as your liking, edit your video with multiple template effects, and play almost all kinds of video and audio files freely.

Below are steps on how to convert MP4 to QuickTime supported Formats.

Step 1. Download and Install VideoSolo Free Video Converter

Download the install package from official website and install it.

Step 2. Launch Video Converter and Add Files

Launch the VideoSolo Free Video Converter, click "Add Files" to select the videos you want to convert. As it supports converting multiple files at the same time, you can add a whole folder to the program.

Add Files

Step 3. Choose Output Format

Select an output format that QuickTime supports, such as MOV, which should be taken into first consideration because it is the default format of QuickTime Player.

Choose Output Format

Step 4. Edit Your Video

Click the "Edit" icon. Now you're able to choose a theme to be the opening and ending of your video. Click "Next" to edit video title, author, time, etc. to customize your own video.

Choose Output Format

Step 5. Start Converting Videos

Click "Convert" button to start converting videos to be playing with QuickTime.

Converting Videos

With the VideoSolo Free Video Converter, we can solve the MP4 video not playing in QuickTime issue easily and freely. For further strong features, I will recommend its upgrade version – VideoSolo Video Converter Ultimate. Similar to the free converter, it also supports conversion among 300+ formats. One of the strong features is that the speed of file conversion is 6X fast than the free version. The ultimate version is a one-stop tool to convert, edit and enhance videos. The edit function is not as basic as free version. The ultimate converter also supports editing functions like clip, crop, rotate, watermark and so on. It's useful and convenient to use this converter due to the user-friendly design it provides.