Short version
MP3 is basically a compressed music file. You will need a player to
listen to mp3s. It takes about 10
times less space than a regular CD track, making it great to use on
the Internet.
Basic Info
MP3, also known as Motion Picture Experts Group Audio Layer 3 (MPEG
Audio Layer 3), is an audio compression codec for use with home computers
and consumer electronics. MP3 was standardized by the Moving Picture
Experts Group (MPEG) to be used as a high performance compression scheme
that uses encoding techniques that can achieve a up to a 12:1 compression
ratio, compared to CD Audio. The relatively small size of MP3 files
allows for efficient storage on computer hard disks, and has become
the standard for music distribution over the web.
Technical Info
The MPEG 1 Layer 3 algorithm is based on a very complicated psycho-acoustic
model. This model is based on the capability of eliminating those frequencies
which the human ear is unable to hear. This compression algorithm can't
be compared to ZIP because it destructs some audio parts which will
never be reconstructed, that's why MP3 can't reach exact CD quality.
In fact, according to Fraunhofer institute, "In all international
listening tests, MPEG Layer-3 impressively proved its superior performance,
maintaining the original sound quality at a data reduction of 1:12 (around
64 kbit/s per audio channel)." This same institute has devised
MP3 algorythm that was previously standardized by ISO (ISO 11172-3 and
13818-3) and developed a non-ISO extension "MPEG 2.5". 1:12
means that you can get a file around 12 times smaller than uncompressed
CD quality without major noticeable difference for your ears.
MP3 are divided into two bitrate categories: constant and variable
(aka VBR; variable bitrate). Using constant bitrate, it's easy to predict
the final file length. For example, a 60 minutes encoded at 128kbps
would take about 57mb. Xing introduced variable bitrate a while ago
which is a part of the ISO standard, but wasn't used by any other encoder.
The only way to know how much space your file will take with VBR is
to encode it and wait for the final result.
