g72x.h

CCITT G.711,G.721,G.723语音压缩算法

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/*
 * g72x.h
 *
 * Header file for CCITT conversion routines.
 *
 */
#ifndef _G72X_H
#define	_G72X_H

#define	AUDIO_ENCODING_ULAW	(1)	/* ISDN u-law */
#define	AUDIO_ENCODING_ALAW	(2)	/* ISDN A-law */
#define	AUDIO_ENCODING_LINEAR	(3)	/* PCM 2's-complement (0-center) */

/*
 * The following is the definition of the state structure
 * used by the G.721/G.723 encoder and decoder to preserve their internal
 * state between successive calls.  The meanings of the majority
 * of the state structure fields are explained in detail in the
 * CCITT Recommendation G.721.  The field names are essentially indentical
 * to variable names in the bit level description of the coding algorithm
 * included in this Recommendation.
 */
struct g72x_state {
	long yl;	/* Locked or steady state step size multiplier. */
	short yu;	/* Unlocked or non-steady state step size multiplier. */
	short dms;	/* Short term energy estimate. */
	short dml;	/* Long term energy estimate. */
	short ap;	/* Linear weighting coefficient of 'yl' and 'yu'. */

	short a[2];	/* Coefficients of pole portion of prediction filter. */
	short b[6];	/* Coefficients of zero portion of prediction filter. */
	short pk[2];	/*
			 * Signs of previous two samples of a partially
			 * reconstructed signal.
			 */
	short dq[6];	/*
			 * Previous 6 samples of the quantized difference
			 * signal represented in an internal floating point
			 * format.
			 */
	short sr[2];	/*
			 * Previous 2 samples of the quantized difference
			 * signal represented in an internal floating point
			 * format.
			 */
	char td;	/* delayed tone detect, new in 1988 version */
};

/* External function definitions. */

extern void g72x_init_stat(struct g72x_state *);
extern int g721_encoder(
		int sample,
		int in_coding,
		struct g72x_state *state_ptr);
extern int g721_decoder(
		int code,
		int out_coding,
		struct g72x_state *state_ptr);
extern int g723_24_encoder(
		int sample,
		int in_coding,
		struct g72x_state *state_ptr);
extern int g723_24_decoder(
		int code,
		int out_coding,
		struct g72x_state *state_ptr);
extern int g723_40_encoder(
		int sample,
		int in_coding,
		struct g72x_state *state_ptr);
extern int g723_40_decoder(
		int code,
		int out_coding,
		struct g72x_state *state_ptr);

#endif /* !_G72X_H */