File: audio.c

package info (click to toggle)
guvcview 2.2.2-1
  • links: PTS, VCS
  • area: main
  • in suites: forky, sid
  • size: 3,748 kB
  • sloc: ansic: 26,250; cpp: 3,786; makefile: 28
file content (854 lines) | stat: -rw-r--r-- 20,119 bytes parent folder | download | duplicates (2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
/******************************************************************************#
#           guvcview              http://guvcview.sourceforge.net              #
#                                                                              #
#           Paulo Assis <pj.assis@gmail.com>                                   #
#           Nobuhiro Iwamatsu <iwamatsu@nigauri.org>                           #
#                             Add UYVY color support(Macbook iSight)           #
#           Flemming Frandsen <dren.dk@gmail.com>                              #
#                             Add VU meter OSD                                 #
#                                                                              #
# This program is free software; you can redistribute it and/or modify         #
# it under the terms of the GNU General Public License as published by         #
# the Free Software Foundation; either version 2 of the License, or            #
# (at your option) any later version.                                          #
#                                                                              #
# This program is distributed in the hope that it will be useful,              #
# but WITHOUT ANY WARRANTY; without even the implied warranty of               #
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the                #
# GNU General Public License for more details.                                 #
#                                                                              #
# You should have received a copy of the GNU General Public License            #
# along with this program; if not, write to the Free Software                  #
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA    #
#                                                                              #
*******************************************************************************/

/******************************************************************************
# # #  Audio library # # #
*******************************************************************************/

#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <unistd.h>
/* support for internationalization - i18n */
#include <libintl.h>
#include <locale.h>

#include "audio.h"
#include "audio_portaudio.h"
#include "gview.h"
#include "gviewaudio.h"
#if HAS_PULSEAUDIO
#include "audio_pulseaudio.h"
#endif

#define AUDBUFF_NUM 80                     /*number of audio buffers*/
#define AUDBUFF_FRAMES 1152                /*number of audio frames per buffer*/
static audio_buff_t *audio_buffers = NULL; /*pointer to buffers list*/
static int buffer_read_index = 0;          /*current read index of buffer list*/
static int buffer_write_index = 0; /*current write index of buffer list*/

int audio_verbosity = 0;

/*
 * set audio_verbosity
 * args:
 *   value - verbosity value
 *
 * asserts:
 *    none
 *
 * returns: none
 */
void audio_set_verbosity(int value) { audio_verbosity = value; }

/*
 * Lock the mutex
 * args:
 *   none
 *
 * asserts:
 *   none
 *
 * returns: none
 */
void audio_lock_mutex(audio_context_t *audio_ctx) {
  __LOCK_MUTEX(&(audio_ctx->mutex));
}

/*
 * Unlock the mutex
 * args:
 *   none
 *
 * asserts:
 *   none
 *
 * returns: none
 */
void audio_unlock_mutex(audio_context_t *audio_ctx) {
  __UNLOCK_MUTEX(&(audio_ctx->mutex));
}

/*
 * free audio buffers
 * args:
 *    none
 *
 * asserts:
 *    none
 *
 * returns: error code
 */
static void audio_free_buffers() {
  buffer_read_index = 0;
  buffer_write_index = 0;

  /*return if no buffers set*/
  if (!audio_buffers) {
    if (audio_verbosity > 0)
      fprintf(stderr, "AUDIO: can't free audio buffers (audio_free_buffers): "
                      "audio_buffers is null\n");
    return;
  }

  int i = 0;

  for (i = 0; i < AUDBUFF_NUM; ++i) {
    free(audio_buffers[i].data);
  }

  free(audio_buffers);
  audio_buffers = NULL;
}

/*
 * alloc a single audio buffer
 * args:
 *    audio_ctx - pointer to audio context data
 *
 * asserts:
 *    none
 *
 * returns: pointer to newly allocate audio buffer or NULL on error
 *   must be freed with audio_delete_buffer
 * data is allocated for float(32 bit) samples but can also store
 * int16 (16 bit) samples
 */
audio_buff_t *audio_get_buffer(audio_context_t *audio_ctx) {
  if (audio_ctx->capture_buff_size <= 0) {
    fprintf(stderr, "AUDIO: (get_buffer) invalid capture_buff_size(%i)\n",
            audio_ctx->capture_buff_size);
    return NULL;
  }

  audio_buff_t *audio_buff = calloc(1, sizeof(audio_buff_t));

  if (audio_buff == NULL) {
    fprintf(stderr,
            "AUDIO: FATAL memory allocation failure (audio_get_buffer): %s\n",
            strerror(errno));
    exit(-1);
  }

  audio_buff->data = calloc(audio_ctx->capture_buff_size, sizeof(sample_t));

  if (audio_buff->data == NULL) {
    fprintf(stderr,
            "AUDIO: FATAL memory allocation failure (audio_get_buffer): %s\n",
            strerror(errno));
    exit(-1);
  }

  return audio_buff;
}

/*
 * deletes a single audio buffer
 * args:
 *    audio_buff - pointer to audio_buff_t data
 *
 * asserts:
 *    none
 *
 * returns: none
 */
void audio_delete_buffer(audio_buff_t *audio_buff) {
  if (!audio_buff)
    return;

  if (audio_buff->data)
    free(audio_buff->data);

  free(audio_buff);
}

/*
 * alloc audio buffers
 * args:
 *    audio_ctx - pointer to audio context data
 *
 * asserts:
 *    none
 *
 * returns: error code
 */
static int audio_init_buffers(audio_context_t *audio_ctx) {
  if (!audio_ctx)
    return -1;

  /*don't allocate if no audio*/
  if (audio_ctx->api == AUDIO_NONE) {
    audio_buffers = NULL;
    return 0;
  }

  int i = 0;

  /*set the buffers size*/
  if (!audio_ctx->capture_buff_size)
    audio_ctx->capture_buff_size = audio_ctx->channels * AUDBUFF_FRAMES;

  if (audio_ctx->capture_buff)
    free(audio_ctx->capture_buff);

  audio_ctx->capture_buff =
      calloc(audio_ctx->capture_buff_size, sizeof(sample_t));

  if (audio_ctx->capture_buff == NULL) {
    fprintf(stderr,
            "AUDIO: FATAL memory allocation failure (audio_init_buffers): %s\n",
            strerror(errno));
    exit(-1);
  }

  /*free audio_buffers (if any)*/
  audio_free_buffers();

  audio_buffers = calloc(AUDBUFF_NUM, sizeof(audio_buff_t));

  if (audio_buffers == NULL) {
    fprintf(stderr,
            "AUDIO: FATAL memory allocation failure (audio_init_buffers): %s\n",
            strerror(errno));
    exit(-1);
  }

  for (i = 0; i < AUDBUFF_NUM; ++i) {
    audio_buffers[i].data =
        calloc(audio_ctx->capture_buff_size, sizeof(sample_t));

    if (audio_buffers[i].data == NULL) {
      fprintf(
          stderr,
          "AUDIO: FATAL memory allocation failure (audio_init_buffers): %s\n",
          strerror(errno));
      exit(-1);
    }

    audio_buffers[i].flag = AUDIO_BUFF_FREE;
  }

  return 0;
}

/*
 * fill a audio buffer data and move write index to next one
 * args:
 *   audio_ctx - pointer to audio context data
 *   ts - timestamp for end of data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_fill_buffer(audio_context_t *audio_ctx, int64_t ts) {
  /*assertions*/
  assert(audio_ctx != NULL);

  if (audio_verbosity > 3)
    printf("AUDIO: filling buffer ts:%" PRId64 "\n", ts);

  /*in nanosec*/
  uint64_t frame_length = NSEC_PER_SEC / audio_ctx->samprate;
  uint64_t buffer_length =
      frame_length * (audio_ctx->capture_buff_size / audio_ctx->channels);

  audio_ctx->current_ts += buffer_length; /*buffer end time*/

  audio_ctx->ts_drift = audio_ctx->current_ts - ts;

  /*get the current write indexed buffer flag*/
  audio_lock_mutex(audio_ctx);
  int flag = audio_buffers[buffer_write_index].flag;
  audio_unlock_mutex(audio_ctx);

  if (flag == AUDIO_BUFF_USED) {
    fprintf(stderr, "AUDIO: write buffer(%i) is still in use - dropping data\n",
            buffer_write_index);
    return;
  }

  /*write max_frames and fill a buffer*/
  memcpy(audio_buffers[buffer_write_index].data, audio_ctx->capture_buff,
         audio_ctx->capture_buff_size * sizeof(sample_t));
  /*buffer begin time*/
  audio_buffers[buffer_write_index].timestamp =
      audio_ctx->current_ts - buffer_length;

  if (audio_buffers[buffer_write_index].timestamp < 0)
    fprintf(stderr,
            "AUDIO: write buffer(%i) - invalid timestamp (< 0): cur_ts:%" PRId64
            " buf_length:%" PRId64 "\n",
            buffer_write_index, audio_ctx->current_ts, buffer_length);

  audio_buffers[buffer_write_index].level_meter[0] =
      audio_ctx->capture_buff_level[0];
  audio_buffers[buffer_write_index].level_meter[1] =
      audio_ctx->capture_buff_level[1];

  audio_lock_mutex(audio_ctx);
  audio_buffers[buffer_write_index].flag = AUDIO_BUFF_USED;
  NEXT_IND(buffer_write_index, AUDBUFF_NUM);
  audio_unlock_mutex(audio_ctx);
}

/* saturate float samples to int16 limits*/
static int16_t clip_int16(float in) {
  // int16_t out = (int16_t) (in < -32768) ? -32768 : (in > 32767) ? 32767 : in;

  long lout = lroundf(in);
  int16_t out = (lout < INT16_MIN)   ? INT16_MIN
                : (lout > INT16_MAX) ? INT16_MAX
                                     : (int16_t)lout;
  return (out);
}

/*
 * get the next used buffer from the ring buffer
 * args:
 *   audio_ctx - pointer to audio context
 *   buff - pointer to an allocated audio buffer
 *   type - type of data (SAMPLE_TYPE_[INT16|FLOAT])
 *   mask - audio fx mask
 *
 * asserts:
 *   none
 *
 * returns: error code
 */
int audio_get_next_buffer(audio_context_t *audio_ctx, audio_buff_t *buff,
                          int type, uint32_t mask) {
  audio_lock_mutex(audio_ctx);
  int flag = audio_buffers[buffer_read_index].flag;
  audio_unlock_mutex(audio_ctx);

  if (flag == AUDIO_BUFF_FREE)
    return 1; /*all done*/

  /*aplly fx*/
  audio_fx_apply(audio_ctx, (sample_t *)audio_buffers[buffer_read_index].data,
                 mask);

  /*copy data into requested format type*/
  int i = 0;

  switch (type) {

  case GV_SAMPLE_TYPE_FLOAT: {
    sample_t *my_data = (sample_t *)buff->data;
    memcpy(my_data, audio_buffers[buffer_read_index].data,
           audio_ctx->capture_buff_size * sizeof(sample_t));
    break;
  }

  case GV_SAMPLE_TYPE_INT16: {
    int16_t *my_data = (int16_t *)buff->data;
    sample_t *buff_p = (sample_t *)audio_buffers[buffer_read_index].data;
    for (i = 0; i < audio_ctx->capture_buff_size; ++i) {
      my_data[i] = clip_int16((buff_p[i]) * INT16_MAX);
    }
    break;
  }

  case GV_SAMPLE_TYPE_FLOATP: {
    int j = 0;

    float *my_data[audio_ctx->channels];
    sample_t *buff_p = (sample_t *)audio_buffers[buffer_read_index].data;

    for (j = 0; j < audio_ctx->channels; ++j)
      my_data[j] =
          (float *)(((float *)buff->data) +
                    (j * audio_ctx->capture_buff_size / audio_ctx->channels));

    for (i = 0; i < audio_ctx->capture_buff_size / audio_ctx->channels; ++i)
      for (j = 0; j < audio_ctx->channels; ++j) {
        my_data[j][i] = *buff_p++;
      }
    break;
  }

  case GV_SAMPLE_TYPE_INT16P: {
    int j = 0;

    int16_t *my_data[audio_ctx->channels];
    sample_t *buff_p = (sample_t *)audio_buffers[buffer_read_index].data;

    for (j = 0; j < audio_ctx->channels; ++j)
      my_data[j] =
          (int16_t *)(((int16_t *)buff->data) +
                      (j * audio_ctx->capture_buff_size / audio_ctx->channels));

    for (i = 0; i < audio_ctx->capture_buff_size / audio_ctx->channels; ++i)
      for (j = 0; j < audio_ctx->channels; ++j) {
        my_data[j][i] = clip_int16((*buff_p++) * INT16_MAX);
      }
    break;
  }

  } // end switch

  buff->timestamp = audio_buffers[buffer_read_index].timestamp;

  buff->level_meter[0] = audio_buffers[buffer_read_index].level_meter[0];
  buff->level_meter[1] = audio_buffers[buffer_read_index].level_meter[1];

  audio_lock_mutex(audio_ctx);
  audio_buffers[buffer_read_index].flag = AUDIO_BUFF_FREE;
  NEXT_IND(buffer_read_index, AUDBUFF_NUM);
  audio_unlock_mutex(audio_ctx);

  return 0;
}

/*
 * audio initialization
 * args:
 *   api - audio API to use
 *           (AUDIO_NONE, AUDIO_PORTAUDIO, AUDIO_PULSE, ...)
 *   device - api device index to use (-1 - use api default)
 *
 * asserts:
 *   none
 *
 * returns: pointer to audio context data (or NULL on error)
 */
audio_context_t *audio_init(int api, int device) {
  audio_context_t *audio_ctx = calloc(1, sizeof(audio_context_t));

  if (audio_ctx == NULL) {
    fprintf(stderr, "AUDIO: (audio_init) couldn't allocate audio context\n");
    return NULL;
  }

  /*initialize the mutex*/
  __INIT_MUTEX(&(audio_ctx->mutex));

  int ret = 0;

  switch (api) {

  case AUDIO_NONE:
    audio_ctx->api = AUDIO_NONE;
    break;

#if HAS_PULSEAUDIO
  case AUDIO_PULSE:
    ret = audio_init_pulseaudio(audio_ctx);
    break;
#endif

  case AUDIO_PORTAUDIO:
  default:
    ret = audio_init_portaudio(audio_ctx);
    break;
  } // end switch

  /*if api couldn't be initialized set audio to none*/
  if (ret != 0)
    audio_ctx->api = AUDIO_NONE;

  /*set default api device*/
  audio_set_device_index(audio_ctx, device);

  /*force a valid number of channels*/
  if (audio_ctx->channels > 2)
    audio_ctx->channels = 2;

  return audio_ctx;
}

/*
 * get audio api
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: audio API
 */
int audio_get_api(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->api;
}

/*
 * set the audio device index to use
 * args:
 *   audio_ctx - pointer to audio context data
 *   index - device index (from device list) to set
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_set_device_index(audio_context_t *audio_ctx, int index) {
  /*assertions*/
  assert(audio_ctx != NULL);

  switch (audio_ctx->api) {

  case AUDIO_NONE:
    break;

#if HAS_PULSEAUDIO
  case AUDIO_PULSE:
    audio_set_pulseaudio_device(audio_ctx, index);
    break;
#endif

  case AUDIO_PORTAUDIO:
  default:
    audio_set_portaudio_device(audio_ctx, index);
    break;
  } // end switch
}

/*
 * get the current audio device index
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: current device index (from device list)
 */
int audio_get_device_index(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->device;
}

/*
 * get the number of available input audio devices
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: number of listed audio devices
 */
int audio_get_num_inp_devices(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->num_input_dev;
}

/*
 * get the audio device referenced by index
 * args:
 *   audio_ctx - pointer to audio context data
 *   index - index of audio device
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: audio device referenced by index
 */
audio_device_t *audio_get_device(audio_context_t *audio_ctx, int index) {
  /*assertions*/
  assert(audio_ctx != NULL);

  if (index >= audio_ctx->num_input_dev) {
    fprintf(stderr, "AUDIO: (audio_get_device) bad index %i using %i\n", index,
            audio_ctx->num_input_dev - 1);
    index = audio_ctx->num_input_dev - 1;
  }

  if (index < 0) {
    fprintf(stderr, "AUDIO: (audio_get_device) bad index %i using 0\n", index);
    index = 0;
  }

  return &audio_ctx->list_devices[index];
}

/*
 * set the current latency
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_set_latency(audio_context_t *audio_ctx, double latency) {
  /*assertions*/
  assert(audio_ctx != NULL);

  audio_ctx->latency = latency;
}

/*
 * get the current latency
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: defined lantency
 */
double audio_get_latency(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->latency;
}

/*
 * set the number of channels
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_set_channels(audio_context_t *audio_ctx, int channels) {
  /*assertions*/
  assert(audio_ctx != NULL);

  audio_ctx->channels = channels;
}

/*
 * get the number of channels
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: number of channels
 */
int audio_get_channels(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->channels;
}

/*
 * set the sample rate
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_set_samprate(audio_context_t *audio_ctx, int samprate) {
  /*assertions*/
  assert(audio_ctx != NULL);

  audio_ctx->samprate = samprate;
}

/*
 * get the sample rate
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: sample rate
 */
int audio_get_samprate(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  return audio_ctx->samprate;
}

/*
 * set the capture buffer size
 * args:
 *   audio_ctx - pointer to audio context data
 *   size - capture buffer size in bytes
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_set_cap_buffer_size(audio_context_t *audio_ctx, int size) {
  /*assertions*/
  assert(audio_ctx != NULL);

  if (audio_verbosity > 2)
    printf("AUDIO: set capture buffer size to %i samples\n", size);

  audio_ctx->capture_buff_size = size;
}

/*
 * start audio stream capture
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: error code
 */
int audio_start(audio_context_t *audio_ctx) {
  if (audio_verbosity > 1)
    printf("AUDIO: starting audio capture\n");

  /*assertions*/
  assert(audio_ctx != NULL);

  /*alloc the ring buffer*/
  audio_init_buffers(audio_ctx);

  /*reset timestamp values*/
  audio_ctx->current_ts = 0;
  audio_ctx->last_ts = 0;
  audio_ctx->snd_begintime = 0;
  audio_ctx->ts_drift = 0;

  int err = 0;

  switch (audio_ctx->api) {

  case AUDIO_NONE:
    break;

#if HAS_PULSEAUDIO
  case AUDIO_PULSE:
    err = audio_start_pulseaudio(audio_ctx);
    break;
#endif

  case AUDIO_PORTAUDIO:
  default:
    err = audio_start_portaudio(audio_ctx);
    break;
  } // end switch

  return err;
}

/*
 * stop audio stream capture
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: error code
 */
int audio_stop(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  int err = 0;

  switch (audio_ctx->api) {

  case AUDIO_NONE:
    break;

#if HAS_PULSEAUDIO
  case AUDIO_PULSE:
    err = audio_stop_pulseaudio(audio_ctx);
    break;
#endif

  case AUDIO_PORTAUDIO:
  default:
    err = audio_stop_portaudio(audio_ctx);
    break;
  } // end switch

  /*free the ring buffer (if any)*/
  audio_free_buffers();

  return err;
}

/*
 * close and clean audio context
 * args:
 *   audio_ctx - pointer to audio context data
 *
 * asserts:
 *   audio_ctx is not null
 *
 * returns: none
 */
void audio_close(audio_context_t *audio_ctx) {
  /*assertions*/
  assert(audio_ctx != NULL);

  audio_fx_close();

  /* thread must be joined before destroying the mutex
   * so no need to unlock before destroying it
   */

  /*destroy the mutex*/
  __CLOSE_MUTEX(&(audio_ctx->mutex));

  switch (audio_ctx->api) {

  case AUDIO_NONE:
    break;

#if HAS_PULSEAUDIO
  case AUDIO_PULSE:
    audio_close_pulseaudio(audio_ctx);
    break;
#endif

  case AUDIO_PORTAUDIO:
  default:
    audio_close_portaudio(audio_ctx);
    break;
  } // end switch

  if (audio_buffers != NULL)
    audio_free_buffers();
}