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.
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3g2 was originally developed by the 3rd Generation Partnership Project 2. It is an audio and video format for use on 3G phones. It can also be played on some 2G and 4G phones. It is designed for transmitting multimedia files over the internet and is mainly used for viewing videos on mobile phones. 3G2 is also known as 3GPP2 which is based on the MPEG-4 standard which was derived from Apple's QuickTime. You are probably familiar with it if you have an Iphone.
3g2 is very much like MPEG-4 Part 14 (MP4) but a much more simplified version of it. It is designed to reduce bandwidth requirements in order to accommodate mobile phones. It is also designed to decrease storage - it stores video streams as MPEG-4 Part 2 or MPEG-4 part 10. It stores audio streams such as AMR-WB, AMR-NB, AMR-WB+, HE-AAC or AAC-LC. The idea is that 3g2 stores and transfers the most significant bytes first.
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