silence_gen.h

00001 /*
00002  * SpanDSP - a series of DSP components for telephony
00003  *
00004  * silence_gen.c - A silence generator, for inserting timed silences.
00005  *
00006  * Written by Steve Underwood <steveu@coppice.org>
00007  *
00008  * Copyright (C) 2006 Steve Underwood
00009  *
00010  * All rights reserved.
00011  *
00012  * This program is free software; you can redistribute it and/or modify
00013  * it under the terms of the GNU General Public License version 2, as
00014  * published by the Free Software Foundation.
00015  *
00016  * This program is distributed in the hope that it will be useful,
00017  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00018  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
00019  * GNU General Public License for more details.
00020  *
00021  * You should have received a copy of the GNU General Public License
00022  * along with this program; if not, write to the Free Software
00023  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
00024  *
00025  * $Id: silence_gen.h,v 1.7 2007/04/08 08:16:18 steveu Exp $
00026  */
00027 
00028 #if !defined(_SPANDSP_SILENCE_GEN_H_)
00029 #define _SPANDSP_SILENCE_GEN_H_
00030 
00031 typedef struct
00032 {
00033     int remaining_samples;
00034     int total_samples;
00035 } silence_gen_state_t;
00036 
00037 #if defined(__cplusplus)
00038 extern "C"
00039 {
00040 #endif
00041 
00042 /*! Generate a block of silent audio samples.
00043     \brief Generate a block of silent audio samples.
00044     \param s The silence generator context.
00045     \param amp The audio sample buffer.
00046     \param max_len The number of samples to be generated.
00047     \return The number of samples actually generated. This will be zero when
00048             there is nothing to send.
00049 */
00050 int silence_gen(silence_gen_state_t *s, int16_t *amp, int max_len);
00051 
00052 /*! Set a silence generator context to output continuous silence.
00053     \brief Set a silence generator context to output continuous silence.
00054     \param s The silence generator context.
00055 */
00056 void silence_gen_always(silence_gen_state_t *s);
00057 
00058 /*! Set a silence generator context to output a specified period of silence.
00059     \brief Set a silence generator context to output a specified period of silence.
00060     \param s The silence generator context.
00061     \param silent_samples The number of samples to be generated.
00062 */
00063 void silence_gen_set(silence_gen_state_t *s, int silent_samples);
00064 
00065 /*! Alter the period of a silence generator context by a specified amount.
00066     \brief Alter the period of a silence generator context by a specified amount.
00067     \param s The silence generator context.
00068     \param silent_samples The number of samples to change the setting by. A positive number
00069                           increases the duration. A negative number reduces it. The duration
00070                           is prevented from going negative.
00071 */
00072 void silence_gen_alter(silence_gen_state_t *s, int silent_samples);
00073 
00074 /*! Find how long a silence generator context has to run.
00075     \brief Find how long a silence generator context has to run.
00076     \param s The silence generator context.
00077     \return The number of samples remaining.
00078 */
00079 int silence_gen_remainder(silence_gen_state_t *s);
00080 
00081 /*! Find the total silence generated to date by a silence generator context.
00082     \brief Find the total silence generated to date.
00083     \param s The silence generator context.
00084     \return The number of samples generated.
00085 */
00086 int silence_gen_generated(silence_gen_state_t *s);
00087 
00088 /*! Initialise a timed silence generator context.
00089     \brief Initialise a timed silence generator context.
00090     \param s The silence generator context.
00091     \param the initial number of samples to set the silence to.
00092     \return A pointer to the silence generator context.
00093 */
00094 silence_gen_state_t *silence_gen_init(silence_gen_state_t *s, int silent_samples);
00095 
00096 #if defined(__cplusplus)
00097 }
00098 #endif
00099 
00100 #endif
00101 /*- End of file ------------------------------------------------------------*/

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