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Understanding MPEG-4 Audio Profiles

Here's an overview that will help you with understanding MPEG-4 Audio Profiles. MPEG-4 Audio profiles are being used in podcasting, XM Satellite Radio and Video Streaming on the web. At the heart of these types of implementations is the MPEG-4 standard which boasts some audio codecs that provide greater compression efficiency. MPEG-4's AAC codec provides significant improvements over MP3. Likewise, HE-AAC provides significant improvements over AAC at a given bit rate.

Now the MPEG-4 standard uses profiles, which are groups of tools that allow users the ability to choose from a variety of toolsets supporting the functionality they need. So think of profiles as having certain features. Since profiles occur at different levels it provides a way to limit computational complexity. The lower the profile the easier it is to playback the content. The higher the profile is the more difficult is is to playback the content.

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Here is a list of Audio Profiles for MPEG-4 and their features:

High-Quality Audio - Includes the most popular AAC object type, AAC Low Complexity, and the CELP speech coder

Low Delay Audio - A variant of the AAC codec with ~ 20ms delay, suitable for high-quality conferences or conversations

High Efficiency AAC Audio - Adds Spectral Band Replication tool to improve coding efficiency at low bitrates

HE-AAC v2 Audio - Add Parametric Stereo Tool to further improve coding efficiency at low bitrates.

Here's a note about encoding for audio compatibility on a device. For example, if you know that a device accepts MPEG-4 audio but you are not sure what profiles are supported then you should use the lowest MPEG-4 audio profile which is AAC Low Complexity.

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