The MPEG-4 Part 14 or MP4 format, which is marked by the extension MP4 as avi and mov a container format. It is based on Apple Quicktime.
These files can contain video and / or multiple audio streams as well as subtitle text and images. It also supports multimedia content such as 2D and 3D data, menus or interactive content. Theoretically, almost any type of data can be included in an mp4, but this is not widely supported.
The video and data streams can be coded in different compression methods.
Supported MPEG 1, 2 and 4. MPEG 4 contains such codecs as Xvid, Divx and H264 and is mostly used. Audio can be in AAC, MP3, MP2 or AC3. There are other special codecs supported. Most commonly AAC is used.
MP4 files can also contain additional metadata.
The contents of the file may also be protected by DRM (Digital Rights Management). Then you need a corresponding, possibly paid license to view the content.
For MP4 files, which contain only one type of data, other endings come into use. m4v for video, m4a for audio, m4b for audiobooks.
Often, portable hardware players are referred to as MP4 players if they can play videos in addition to audio files. However, this does not mean that they can handle MP4 files.
Most players can handle MP4 files as long as they can decode the data they contain. That's the case with most videos.
Most often resolving problems with opening MP4 files is very simple. Just install an appropriate program that supports such files. All of the listed programs support MP4 files, but may vary in offered function and purpose. Some programs may be capable only of viewing contents of MP4 files or offer file conversion options, but may not be capable of editing such files.
It is possible that although a compatible program has been installed on user’s system, it is not used by the system to open it. This may happen because no default application was associated with this type of files. To associate MP4 files with given application, select "Open with" from drop-down menu (accessed by right-clicking on the file). Then select from the list the program or application you want to be used to open this type of file. If the QuickTime Player applications is not on the list, select "Browse" option in order to manually locate the directory where QuickTime Player has been installed.
Sometimes problems with opening MP4 files may not lie with the application itself, but can arise due to other causes, such as: