dmG726Decode(3dm)					     dmG726Decode(3dm)

NAME    [Toc]    [Back]

     dmG726Decode - implements ITU (International Telecommunication Union)
     Recommendation G.726 ADPCM	decompression for input	compressed bit stream
     of	40, 32 ,24, or 16 kbit/s and output data of 64 kbit/s A-law, mu-law,
     or	linear PCM.  G.726 replaced G.721 and G.723.

SYNOPSIS    [Toc]    [Back]

     #include <dmedia/dm_audioutil.h>

     DMstatus dmG726Decode(DMG726decoder handle,
			   unsigned char *inBuffer,
			   void	*outBuffer,
			   int numSamples)

PARAMETER    [Toc]    [Back]

     handle    DMG726decoder structure,	created	by dmG726DecoderCreate(3dm),
	       specifies the signal processing parameters.


     ibuf      pointer to input	compressed data	buffer,	an array of bytes. The
	       data format is unsigned char (8-bit).  The input	bitstrem
	       buffer consists of a multiple of	1, 3, 1, or 5 bytes, for
	       operations at 16, 24, 32, or 40 kbit/s respectively.


     obuf      pointer to output sample	data buffer, an	array of short (16
	       bits) for linear	output or unsigned char	for A-law or mu-law
	       output.	For linear output, samples are assumed to be two's
	       complement.  Data buffer	must be	a multiple (the	same multiple
	       as that of input	bitstrem buffer) of 4, 8, 2, or	8 for
	       operations at 16, 24, 32, or 40 kbit/s respectively.  This
	       assumes the sampling rate of 8 kHz.


     numSamples
	       number of samples to be processed. it must always be a multiple
	       of 4, 8,	2, or 8	for operations at 16, 24, 32, or 40 kbit/s
	       respectively.

RETURNED VALUE    [Toc]    [Back]

     Returns DM_FAILURE	or DM_SUCCESS.

DESCRIPTION    [Toc]    [Back]

     dmG726Decode(3dm) implements the ITU G.726	decompression.	G.726
     decompression decompresses	2, 3, 4, or 5 bits to generate one output
     sample for	16, 24,	32, or 40 kbit/s operations respectively. 16, 24, 32,
     or	40 kbit/s operation is indicated by setting parameter DM_AUDIO_BITRATE
     to	16000, 24000, 32000, or	40000 using DMparams and passed	to



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dmG726Decode(3dm)					     dmG726Decode(3dm)



     dmG726DecoderSetParams(3dm).  Output format is indicated by setting
     DM_G726_NATIVE_FORMAT to AUDIO_ENCODING_ULAW, AUDIO_ENCODING_ALAW,	or
     AUDIO_ENCODING_LINEAR, respectively for outputting	mu-law,	A-law, or
     linear PCM	data, using DMparams and passed	to
     dmG726DecoderSetParams(3dm).  If output mode is AUDIO_ENCODING_LINEAR,
     the PCM data type will be short.  Otherwise, the PCM data type will be
     unsigned char.  Therefore,	obuf is	void in	the function prototyping.

NOTE    [Toc]    [Back]

     G.726 algorithm was developed for sampling	rate of	8 kHz, but could be
     used from 8 kHz to	48 kHz.

SEE ALSO    [Toc]    [Back]

     dmG726DecoderCreate(3dm), dmG726DecoderSetParams(3dm),
     dmG726DecoderDestroy(3dm),	dmG726Encode(3dm), ITU (International
     Telecommunication Union) Recommendation G.726.


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