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dmMPEG1AudioDecode(3dm)				       dmMPEG1AudioDecode(3dm)

NAME    [Toc]    [Back]

     dmMPEG1AudioDecode	- decodes a single compressed block of data created by
     a call to dmMPEG1AudioEncode(3dm).

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/dmedia.h>
     #include <dmedia/dm_audioutil.h>

     DMstatus dmMPEG1AudioDecode(DMMPEG1audiodecoder decoder,
					 unsigned char *cmpData,
					 short *output,
					 int *fmtBytes)

PARAMETER    [Toc]    [Back]

     decoder   DMMPEG1audiodecoder structure, created by
	       dmMPEG1AudioDecoderCreate(3dm), specifies and stores the	signal
	       processing parameters.  It describes the	kind of	decompression
	       to perform, and holds the between-block state of	the
	       decompressor.  It is initially generated	and processed by calls
	       to dmMPEG1AudioDecoderCreate(3dm) and
	       dmMPEG1AudioDecoderSetParams(3dm), and is modified on each
	       call.  To get decoder in	the proper state for the first call,
	       see DESCRIPTION below.

     cmpData   points to the next block	of compressed bytes to be decoded.
	       The calling procedure should pass an entire compressed block's
	       worth of	bytes.	Generally, this	amount is unkown and the
	       calling procedure must queue up at least	as many	bytes as
	       returned	from a call to dmMPEG1AudioHeaderGetBlockBytes(3dm) as
	       that is the expected length that	dmMPEG1AudioDecode(3dm)	will

     output    points to a pre-allocated block of memory into which
	       dmMPEG1AudioDecode(3dm) will write the decompressed sample
	       frames. output must be big enough to hold the entire
	       decompressed frame.  Note that all decompressed blocks contain
	       the same	number of sample frames.  A way	to determine this size
	       is described below under	DESCRIPTION.

     fmtBytes  pointer to an integer return value; indicates the actual	number
	       of compressed bytes consumed. By	advancing the index in the
	       compressed data stream by this amount, the next block of
	       compressed data will be located correctly. If the decoder
	       structure or the	compressed data	is malformed, this return will
	       be zero,	indicating an error.

									Page 1

dmMPEG1AudioDecode(3dm)				       dmMPEG1AudioDecode(3dm)

RETURNED VALUE    [Toc]    [Back]

     Returns DM_FAILURE	or DM_SUCCESS.

DESCRIPTION    [Toc]    [Back]

     dmMPEG1AudioDecode(3dm) implements	MPEG1 audio decompression.

     The decoder state parameters need to be initialized before	the first call
     to	dmMPEG1AudioDecode(3dm), after which it	is self-maintaining. DMparam
     *params should be passed to dmMPEG1AudioHeaderGetParams in	order to fill
     in	the params structure from the compressed data header, and find the
     worst-case	buffering requirements for the compressed data.	 Then, a call
     to	dmMPEG1AudioDecoderSetParams(3dm) will set decoding parameter values
     for decoder.  And dmMPEG1AudioDecoderGetParams(3dm) will be used to qurey
     DM_AUDIO_CODEC_FRAMES_PER_BLOCK, which contains the size of decompressed
     blocks for	the compressed stream.

NOTE    [Toc]    [Back]

     compression/decompression delay will be caused by filter operations that
     convolve a	N past input samples with a filter M-coefficient array to
     create N+M-1 output samples.  The filtered	signal contains	more samples
     than the unfiltered signal. the output signal is offset by
     DM_AUDIO_CODEC_FILTER_DELAY samples from the first	sample thus omits the
     last DM_AUDIO_CODEC_FILTER_DELAY samples from the output file.

SEE ALSO    [Toc]    [Back]

     dmMPEG1AudioDecoderCreate(3dm), dmMPEG1AudioDecoderSetParams(3dm),
     dmMPEG1AudioDecoderGetParams(3dm),	dmMPEG1AudioDecoderDestroy(3dm),

									PPPPaaaaggggeeee 2222
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