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dmMPEG1AudioEncoderSetParams(3dm)	     dmMPEG1AudioEncoderSetParams(3dm)


NAME    [Toc]    [Back]

     dmMPEG1AudioEncoderSetParams, dmMPEG1AudioDecoderSetParams,
     dmMPEG1AudioEncoderGetParams, dmMPEG1AudioDecoderGetParams	- set and
     query MPEG1 audio encoder/decoder parameter values.

SYNOPSIS    [Toc]    [Back]

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


     DMstatus dmMPEG1AudioEncoderSetParams(DMMPEG1audioencoder encoder,
				   DMparams *params)
     DMstatus dmMPEG1AudioDecoderSetParams(DMMPEG1audiodecoder decoder,
				   DMparams *params)
     DMstatus dmMPEG1AudioEncoderGetParams(DMMPEG1audioencoder encoder,
				   DMparams *params)
     DMstatus dmMPEG1AudioDecoderGetParams(DMMPEG1audiodecoder decoder,
				   DMparams *params)

PARAMETER    [Toc]    [Back]

     encoder  DMMPEG1audioencoder structure, created by
	      dmMPEG1AudioEncoderCreate(3dm).


     decoder  DMMPEG1audiodecoder structure, created by
	      dmMPEG1AudioDecoderCreate(3dm).


     params   List of parameters for specification.

RETURNED VALUE    [Toc]    [Back]

     Returns DM_SUCCESS	or DM_FAILURE.

DESCRIPTION    [Toc]    [Back]

     dmMPEG1AudioEncoderSetParams(3dm) or dmMPEG1AudioDecoderSetParams(3dm)
     sets MPEG1	audio encoder or decoder parameters to user defined values
     with params.  These values	will overwrite the default values set by
     dmMPEG1AudioEncoderCreate(3dm) or dmMPEG1AudioDecoderSetParams(3dm).
     *params can be NULL, then default values will be used.  Unrecognized
     parameters	are ignored.  dmMPEG1AudioEncoderSetParams(3dm)	or
     dmMPEG1AudioDecoderSetParams(3dm) also initializes	necessary filter
     coefficients for encoder/decoder so it has	to be used before calling
     dmMPEG1AudioEncode(3dm) or	dmMPEG1AudioDecode(3dm). For decoder, user
     defined parameters	usually	should be obtained first by using
     dmMPEG1AudioHeaderGetParams(3dm) from compressed data header.
     dmMPEG1AudioEncoderGetParams(3dm) or dmMPEG1AudioDecoderGetParams(3dm)
     obtains MPEG1 audio encoder or decoder parameters.



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dmMPEG1AudioEncoderSetParams(3dm)	     dmMPEG1AudioEncoderSetParams(3dm)



     The set of	parameters for params are, defined in dmedia/dm_audioutil.h
     and dmedia/dm_params.h are	as follows


     Parameters	for MPEG1 audio	encoder	and decoder:

     DM_AUDIO_RATE    [Toc]    [Back]
     input/output sampling rate	parameter (rate	given in Hz).  The
     corresponding values for the rates	are doubles. 32000, 44100 (default),
     and 48000 Hz are supported.


     DM_AUDIO_FORMAT    [Toc]    [Back]
	  DM_AUDIO_TWOS_COMPLEMENT
     indicates the format of each input/ouput audio sample.
     DM_AUDIO_TWOS_COMPLEMENT is the only value	supported.


     DM_AUDIO_WIDTH    [Toc]    [Back]
	  DM_AUDIO_WIDTH_16
     indicates the width of each input/ouput audio sample.  DM_AUDIO_WIDTH_16
     is	the only value supported.


     DM_AUDIO_CHANNELS    [Toc]    [Back]
     passes the	number of channels in the input/output audio data. Integer 1
     or	2 (default) are	the only values	supported.


     DM_MPEG1_AUDIO_LAYER    [Toc]    [Back]
	  DM_MPEG1_AUDIO_LAYER1
	  DM_MPEG1_AUDIO_LAYER2	 (default)
     a flag specifying the basic algorithm to be used.

     DM_AUDIO_CHANNEL_POLICY    [Toc]    [Back]
	  DM_AUDIO_STEREO
	  DM_AUDIO_JOINT_STEREO	 (default)
	  DM_AUDIO_INDEPENDENT
     chooses how multiple channels should be treaed.
     DM_AUDIO_STEREO indicates that the	channels are part of a single
     multichannel signal. This includes	quadrophonic, etc.;
     DM_AUDIO_JOINT_STEREO indicates that the algorithm	may attempt to exploit
     redundancy	between	channels for greater coding gain;
     DM_AUDIO_INDEPENDENT indicates that the separate channels are unrelated
     and should	be processed separately, such as multilingual sound tracks.


     DM_AUDIO_BITRATE    [Toc]    [Back]
     specifies the desired bitrate for the compressed data, in bits per
     second. Note that for some	schemes	such as	MPEG's maxrate this is treated
     as	an upper limit,	whereas	for MPEG's fixrate, this is strictly achieved
     as	a constant rate. The following is a list of valid bitrates for MPEG1



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dmMPEG1AudioEncoderSetParams(3dm)	     dmMPEG1AudioEncoderSetParams(3dm)



     audio:
     Layer 1: 32000, 64000, 96000, 128000, 160000, 192000, 224000, 256000
     (default),	288000,	320000,	352000,	384000,	416000,	and 448000.
     Layer 2: 32000, 48000, 56000, 64000, 80000, 96000,	112000,	128000,
     160000, 192000, 224000, 256000 (default), 320000, and 384000.


     Parameters	for MPEG1 audio	encoder	only:


     DM_MPEG1_AUDIO_PSYCHOMODEL    [Toc]    [Back]
	  DM_MPEG1_AUDIO_PSYCHOMODEL1
	  DM_MPEG1_AUDIO_PSYCHOMODEL2
     selects which psychoacoustic model	is used	to calculate the safe masking
     thresholds	for quantizing noise (the basis	of the compression).  The
     psychoacoustic model determines when quantization noise may be safely
     hidden below signal components.  The


     DM_MPEG1_AUDIO_PSYCHOMODEL1_ALPHA    [Toc]    [Back]
     specifies possible	float value for	MPEG1 audio psychoacoustic model's
     alpha parameter (only for model 1).  Valid	value is within	(0.0, 2.0].
     Default is	2.0.


     DM_MPEG1_AUDIO_BITRATE_POLICY    [Toc]    [Back]
	  DM_MPEG1_AUDIO_FIXRATE	(default)
	  DM_MPEG1_AUDIO_CONSTANT_QUALITY
     is	a flag to select variants for interpreting DM_AUDIO_BIT_RATE.


     DM_MPEG1_AUDIO_CONST_QUAL_NMR    [Toc]    [Back]
     The argument is the desired mask to noise ratio in	dB. Possible float
     value for this parameter is within	(-13.0,	13.0]. Default is 0.0.
     Positive (negative) values	will make quantization noise more (less)
     audible and result	in smaller (larger) compressed files.


     Parameters	for MPEG1 audio	decoder	only:

     DM_MPEG1_AUDIO_DECIMATION_SCALE    [Toc]    [Back]
	  DM_MPEG1_AUDIO_BANDWIDTH_FULL	(default)
	  DM_MPEG1_AUDIO_BANDWIDTH_HALF
	  DM_MPEG1_AUDIO_BANDWIDTH_QUARTER
     specifies the decimation factor applied to	reduced	complexity of
     decoding. A value of fraction of DM_MPEG1_AUDIO_BANDWIDTH_HALF or
     DM_MPEG1_AUDIO_BANDWIDTH_QUARTER indicates	that the resynthesized stream
     should be at one-half or one- quaner of the nominal sampling rate.	 A
     value of DM_MPEG1_AUDIO_BANDWIDTH_FULL results in normal behavior.






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dmMPEG1AudioEncoderSetParams(3dm)	     dmMPEG1AudioEncoderSetParams(3dm)



     DM_MPEG1_AUDIO_SCALE_FILTERSHAPE    [Toc]    [Back]
	  DM_MPEG1_AUDIO_DEFAULT_FILTER	(default)
	  DM_MPEG1_AUDIO_FILTER_SHAPE1
	  DM_MPEG1_AUDIO_FILTER_SHAPE2
     specifies the filter shape	applied	to reduced complexity of decoding.   A
     value of DM_MPEG1_AUDIO_BANDWIDTH_FULL results in normal behavior.



     DM_MPEG1_AUDIO_COMBINE_CHANS_FLAG    [Toc]    [Back]
     integer, default value is 0; if set to 1, it overwrites the JOINT_STEREO
     mode and force decoder to produce single channel output.


     Parameters	for MPEG1 audio	query only, using
     dmMPEG1AudioEncoderGetParams(3dm) or dmMPEG1AudioDecoderGetParams(3dm):

     DM_AUDIO_CODEC_FRAMES_PER_BLOCK    [Toc]    [Back]
     specifies how many	sample frames (integer)	are put	into each compressed
     data block.  For each call	to dmMPEG1AudioEncode(3dm), this many new
     sample frames must	be provided; each call to dmMPEG1AudioDecode(3dm),
     will return this many new sample frames.

     DM_AUDIO_CODEC_MAX_BYTES_PER_BLOCK    [Toc]    [Back]
     indicates the maximum number of bytes (integer) that will comprise	a
     compressed	data block (representing frames	per block sample frames). For
     compression, this is the size of the output buffer	that must be provided
     to	dmMPEG1AudioEncode(3dm); for decompression, this is the	number of
     compressed	bytes that must	be queued up for dmMPEG1AudioDecode(3dm) to
     look at. Note that	any particular block can be smaller than this; both
     dmMPEG1AudioEncode(3dm) and dmMPEG1AudioDecode(3dm) return	the actual
     byte-size of the given block.

     DM_AUDIO_CODEC_FILTER_DELAY    [Toc]    [Back]
     This is the number	of sample fames	(integer) of delay introduced in
     compression and decompression processing.	These numbers are usually
     different for compression versus decompression.  This is caused by	filter
     operations	that convolve a	N past input samples with a filter Mcoefficient
 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.

NOTE    [Toc]    [Back]

SEE ALSO
     dmMPEG1AudioEncoderCreate(3dm), dmMPEG1AudioEncode(3dm),
     dmMPEG1AudioDecoderCreate(3dm), dmMPEG1AudioDecode(3dm).


									PPPPaaaaggggeeee 4444
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