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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Free Lossless Audio Codec, or FLAC for short, is an audio compression technique. It is a lossless compression type meaning that the compression takes place without data being discarded. FLAC is an open source codec. FLAC is a format that is recommended to those backing up a CD collection because the sound quality will remain high, whereas MP3 compression will result in a deterioration compared to the original.
Using FLAC to compress an audio file to approximately 50% of its original size. The main benefits of a FLAC file in addition to it being lossless is that it can be used for streaming, and decoding is fast, allowing for real time decoding to take place. A FLAC file also contains several data integrity checks in the header file. The metadata associated with the audio has been future proofed also to allow new fields to be defined without impacting existing decoders.