MP4 files (MPEG-4 Part 14) are multimedia files. MP4 is a container format that can store video, audio and subtitle data (as well as more depending on content). Since stores like iTunes uses this container format, and it is used with iPod and PlayStation Portable (PSP), MP4 files have become more common.
MPEG-4 Part 14 or MP4, formally ISO/IEC 14496-14:2003, is a multimedia container format standard specified as a part of MPEG-4. It is most commonly used to store digital video and digital audio streams, especially those defined by MPEG, but can also be used to store other data such as subtitles and still images. Like most modern container formats, MPEG-4 Part 14 allows streaming over the Internet. A separate hint track is used to include streaming information in the file. The only official filename extension for MPEG-4 Part 14 files is .mp4.
Apple QuickTime Player Apple iTunes Microsoft Windows Media Player VideoLAN VLC Media Player
Similar to the MKV file extension, WEBM is a file format developed by a number of parties, including Google. Launched in 2010, it is open source format designed to deliver video through the web. It can be used for a variety of types of video, from video calls to high definition movies. WebM is growing, and by using the HTML5 version of YouTube, it is possible to watch video encoded in WebM.
WebM benefits from being designed for use on the modern web, rather than for local use. This means the format is specifically designed for the wide range of devices that are used to access the web, from Smart Phones to Powerful PCs. The video element of the file is encoded using VP8 video codec and the audio element of the file is encoded using the Vorbis audio codec.
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Google (Previously developed by On2, Xiph, and Matroska)