NAME

acm − Audio Compression Manager APIs for MMS

DESCRIPTION

The Audio Compression Manager APIs for Multimedia Services for Digital UNIX provide the following functionalities:

•Transparent run-time audio compression and decompression

•Wave-data format selection

•Wave-data filter selection

•Wave-data format conversion

•Wave-data filtering

The ACM overrides the default mapping algorithm for wave devices. The ACM manages the following types of drivers:

•Compressor and decompressor (CODEC) drivers

•Format-converter drivers

•Filter drivers

Compressor and decompressor modules change one format type to another. For example, a compressor or decompressor module can change a PCM file to an ADPCM file. Format converter modules change the format, but not the data type. For example, a converter module can change 44-kHz, 16-bit data to 44-kHz, 8- bit data. Filters do not change the data format at all, but change the wave data in some manner. For example, a filter could mix together a data stream and an echo of itself. A single ACM driver, or a filter tag or format tag within a driver, might also support combinations of the above types. For wave output, the ACM passes each buffer to the converter as it arrives. The converter decompresses the data and returns the decompressed data to ACM in a "shadow" buffer. The ACM then passes the decompressed shadow buffer to the wave driver. The ACM allocates the shadow buffers whenever it receives a prepare message. 

For wave input, the ACM passes empty shadow buffers to the driver. The ACM then passes the buffers to the driver for compression. After compression is finished, the driver passes the data to the application. 

SEE ALSO

acmDriverClose.(,), acmDriverDetails.(,), acmDriverEnum.(,), acmDriverId.(,), acmDriverOpen.(,), acmGetVersion.(,), acmMetrics.(,), acmStreamClose.(,), acmStreamConvert.(,), acmStreamOpen.(,), acmStreamPrepareHeader.(,), acmStreamReset.(,), acmStreamSize.(,), acmStreamUnprepareHeader.(,), acm(,), icm(,), mme(,), mmio(,), video(,), wave(,), mms(,), mmsdev(,),
and the Multimedia Services for Digital UNIX Programmer’s Guide.