To resolve this issue, try VLC media player. MP4 is a container that contains various kinds of data, so when there is a problem opening the file, it usually means that data in the container (an audio or video codec) is not compatible with the device’s OS. On some devices, particularly mobile, opening this file type can be problematic. On Windows, it opens in Windows Media Player. Online Video Converter A free web app that converts video files, allowing you to change the video format, resolution or size right in your browser. There is no need for third-party software. Simply double-clicking the file opens it. MP4 files open in the operating system's default video player. Many consider MP4 to be one of the best video formats available today. It is also a popular video format for streaming over the Internet, such as on YouTube. It is compatible with a wide range of devices and operating systems, using a codec to compress file size, resulting in a file that is easy to manage and store.

MPEG-4 (MP4) is a container video format that can store multimedia data, usually audio and video.

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