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Ultimedia Services Version 2 for AIX: Programmer's Guide and Reference

Chapter 25. Audio Codec Objects

The Ultimedia Services programming interface is presented as a binary class library through SOM. This class library provides various objects that can be used to play, record, and edit media files. For example, C language bindings to these SOM object methods generally include two additional arguments: the instance pointer and the environment pointer. See"General Programming Information" for more general information.

An audio codec object is an algorithm for compressing and decompressing digital audio data. The audio codec object consists of two kinds of objects: encoder objects that perform the data compression, and decoder objects that perform the data decompression. These objects are used in applications that store or transmit large amounts of audio data, for example, music archival. Data compression factors of 5:1 can be achieved with only a minimal impact on quality.

Each audio encoder object is a subclass of the UMSFilter object, which means these objects support both common and object specific methods. As each encoder supports a limited number of input sample rates, it might be necessary to use the UMSFilter object to adjust the audio data's sample rate. The audio codec object supports a frame-oriented paradigm, similar to the video codec objects. T he audio codec is configured by calling a series of set methods, then each audio frame is compressed or decompressed.

To learn more about the audio encoder object, see:

                          This object converts audio from PCM16 format into an MPEG-1 format.
                          This object converts monophonic 16-bit PCM data, sampled at 8000 Hz, into G.723 compressed audio.
                          This object converts G.723 compressed data to 8 kilohertz 16-bit PCM audio data.

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