MP3 VS MP4

[Marian Petrides]

Paul,

Not sure this is what you are referring to, but iTunes music store 
downloads have an extension of  .m4p  These files are "protected AAC" 
file, i.e. encrypted Advanced Audio Coding format files.  Unencrypted 
AAC files have an extension of  .m4a

A google search on AAC yielded the following info:

First:     http://www.apple.com/mpeg4/aac/
has a lot of background information and a PDF file MPEG-4 Fact Sheet.


Second:  the following excerpt comes from:
http://www.vialicensing.com/products/mpeg4aac/standard.html

Advanced Audio Coding (AAC) is a wideband audio coding algorithm that 
exploits two primary coding strategies to dramatically reduce the 
amount of data needed to convey high-quality digital audio. First, 
signal components that are "perceptually irrelevant" and can be 
discarded without a perceived loss of audio quality are removed. Next, 
redundancies in the coded audio signal are eliminated. Efficient audio 
compression is achieved by a variety of perceptual audio coding and 
data compression tools, which are combined in the MPEG-4 AAC 
specification.

  The MPEG-4 AAC standard incorporates MPEG-2 AAC, forming the basis of 
the MPEG-4 audio compression technology for data rates above 32 kbps 
per channel. Additional tools increase the effectiveness of AAC at 
lower bit rates, and add scalability or error resilience 
characteristics. These additional tools extend AAC into its MPEG-4 
incarnation (ISO/IEC 14496-3, Subpart 4).

HTH.

Marian




On Dec 27, 2004, at 7:53 PM, Paul Salyers wrote:

>
>
>
> I heard there was a better sound format called MP4. Anyone know any 
> thing about this for sure?
>
>
> Paul Salyers
> PS1 - Senior Rep.
> PS1 at softseven.org
> http://ps1.softseven.org
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