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1 /*
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2 * SpanDSP - a series of DSP components for telephony
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3 *
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4 * silence_gen.c - A silence generator, for inserting timed silences.
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5 *
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6 * Written by Steve Underwood <steveu@coppice.org>
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7 *
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8 * Copyright (C) 2006 Steve Underwood
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9 *
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10 * All rights reserved.
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11 *
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12 * This program is free software; you can redistribute it and/or modify
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13 * it under the terms of the GNU General Public License version 2, as
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14 * published by the Free Software Foundation.
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15 *
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16 * This program is distributed in the hope that it will be useful,
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17 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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18 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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19 * GNU General Public License for more details.
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20 *
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21 * You should have received a copy of the GNU General Public License
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22 * along with this program; if not, write to the Free Software
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23 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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24 *
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25 * $Id: silence_gen.h,v 1.4 2006/10/24 13:45:28 steveu Exp $
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26 */
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27
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28 #if !defined(_SILENCE_GEN_H_)
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29 #define _SILENCE_GEN_H_
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30
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31 typedef struct
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32 {
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33 int remaining_samples;
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34 int total_samples;
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35 } silence_gen_state_t;
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36
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37 #ifdef __cplusplus
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38 extern "C" {
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39 #endif
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40
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41 /*! Generate a block of silent audio samples.
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42 \brief Generate a block of silent audio samples.
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43 \param s The silence generator context.
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44 \param amp The audio sample buffer.
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45 \param max_len The number of samples to be generated.
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46 \return The number of samples actually generated. This will be zero when
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47 there is nothing to send.
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48 */
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49 int silence_gen(silence_gen_state_t *s, int16_t *amp, int max_len);
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50
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51 /*! Set a silence generator context to output continuous silence.
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52 \brief Set a silence generator context to output continuous silence.
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53 \param s The silence generator context.
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54 */
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55 void silence_gen_always(silence_gen_state_t *s);
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56
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57 /*! Set a silence generator context to output a specified period of silence.
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58 \brief Set a silence generator context to output a specified period of silence.
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59 \param s The silence generator context.
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60 \param silent_samples The number of samples to be generated.
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61 */
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62 void silence_gen_set(silence_gen_state_t *s, int silent_samples);
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63
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64 /*! Alter the period of a silence generator context by a specified amount.
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65 \brief Alter the period of a silence generator context by a specified amount.
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66 \param s The silence generator context.
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67 \param silent_samples The number of samples to change the setting by. A positive number
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68 increases the duration. A negative number reduces it. The duration
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69 is prevented from going negative.
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70 */
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71 void silence_gen_alter(silence_gen_state_t *s, int silent_samples);
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72
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73 /*! Find how long a silence generator context has to run.
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74 \brief Find how long a silence generator context has to run.
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75 \param s The silence generator context.
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76 \return The number of samples remaining.
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77 */
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78 int silence_gen_remainder(silence_gen_state_t *s);
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79
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80 /*! Find the total silence generated to date by a silence generator context.
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81 \brief Find the total silence generated to date.
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82 \param s The silence generator context.
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83 \return The number of samples generated.
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84 */
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85 int silence_gen_generated(silence_gen_state_t *s);
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86
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87 /*! Initialise a timed silence generator context.
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88 \brief Initialise a timed silence generator context.
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89 \param s The silence generator context.
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90 \param the initial number of samples to set the silence to.
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91 \return A pointer to the silence generator context.
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92 */
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93 silence_gen_state_t *silence_gen_init(silence_gen_state_t *s, int silent_samples);
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94
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95 #ifdef __cplusplus
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96 }
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97 #endif
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98
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99 #endif
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100 /*- End of file ------------------------------------------------------------*/
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