modules/access/alsa.c

   1 /*****************************************************************************
   2  * alsa.c : Alsa input module for vlc
   3  *****************************************************************************
   4  * Copyright (C) 2002-2009 the VideoLAN team
   5  * $Id$
   6  *
   7  * Authors: Benjamin Pracht <bigben at videolan dot org>
   8  *          Richard Hosking <richard at hovis dot net>
   9  *          Antoine Cellerier <dionoea at videolan d.t org>
  10  *          Dennis Lou <dlou99 at yahoo dot com>
  11  *
  12  * This program is free software; you can redistribute it and/or modify
  13  * it under the terms of the GNU General Public License as published by
  14  * the Free Software Foundation; either version 2 of the License, or
  15  * (at your option) any later version.
  16  *
  17  * This program is distributed in the hope that it will be useful,
  18  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  19  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  20  * GNU General Public License for more details.
  21  *
  22  * You should have received a copy of the GNU General Public License
  23  * along with this program; if not, write to the Free Software
  24  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
  25  *****************************************************************************/
  26
  27 /*
  28  * ALSA support based on parts of
  29  * http://www.equalarea.com/paul/alsa-audio.html
  30  * and hints taken from alsa-utils (aplay/arecord)
  31  * http://www.alsa-project.org
  32  */
  33
  34 /*****************************************************************************
  35  * Preamble
  36  *****************************************************************************/
  37
  38 #ifdef HAVE_CONFIG_H
  39 # include "config.h"
  40 #endif
  41
  42 #include <vlc_common.h>
  43 #include <vlc_plugin.h>
  44 #include <vlc_access.h>
  45 #include <vlc_demux.h>
  46 #include <vlc_input.h>
  47
  48 #include <unistd.h>
  49 #include <sys/ioctl.h>
  50 #include <sys/mman.h>
  51
  52 #include <sys/soundcard.h>
  53
  54 #define ALSA_PCM_NEW_HW_PARAMS_API
  55 #define ALSA_PCM_NEW_SW_PARAMS_API
  56 #include <alsa/asoundlib.h>
  57
  58 #include <poll.h>
  59
  60 /*****************************************************************************
  61  * Module descriptior
  62  *****************************************************************************/
  63
  64 static int  DemuxOpen ( vlc_object_t * );
  65 static void DemuxClose( vlc_object_t * );
  66
  67 #define STEREO_TEXT N_( "Stereo" )
  68 #define STEREO_LONGTEXT N_( \
  69     "Capture the audio stream in stereo." )
  70
  71 #define SAMPLERATE_TEXT N_( "Samplerate" )
  72 #define SAMPLERATE_LONGTEXT N_( \
  73     "Samplerate of the captured audio stream, in Hz (eg: 11025, 22050, 44100, 48000)" )
  74
  75 #define CACHING_TEXT N_("Caching value in ms")
  76 #define CACHING_LONGTEXT N_( \
  77     "Caching value for Alsa captures. This " \
  78     "value should be set in milliseconds." )
  79
  80 #define HELP_TEXT N_( \
  81     "Use alsa:// to open the default audio input. If multiple audio " \
  82     "inputs are available, they will be listed in the vlc debug output. " \
  83     "To select hw:0,1 , use alsa://hw:0,1 ." )
  84
  85 #define ALSA_DEFAULT "hw"
  86 #define CFG_PREFIX "alsa-"
  87
  88 vlc_module_begin()
  89     set_shortname( N_("ALSA") )
  90     set_description( N_("ALSA audio capture input") )
  91     set_category( CAT_INPUT )
  92     set_subcategory( SUBCAT_INPUT_ACCESS )
  93     set_help( HELP_TEXT )
  94
  95     add_shortcut( "alsa" )
  96     set_capability( "access_demux", 10 )
  97     set_callbacks( DemuxOpen, DemuxClose )
  98
  99     add_bool( CFG_PREFIX "stereo", true, NULL, STEREO_TEXT, STEREO_LONGTEXT,
 100                 true )
 101     add_integer( CFG_PREFIX "samplerate", 48000, NULL, SAMPLERATE_TEXT,
 102                 SAMPLERATE_LONGTEXT, true )
 103     add_integer( CFG_PREFIX "caching", DEFAULT_PTS_DELAY / 1000, NULL,
 104                 CACHING_TEXT, CACHING_LONGTEXT, true )
 105 vlc_module_end()
 106
 107 /*****************************************************************************
 108  * Access: local prototypes
 109  *****************************************************************************/
 110
 111 static int DemuxControl( demux_t *, int, va_list );
 112
 113 static int Demux( demux_t * );
 114
 115 static block_t* GrabAudio( demux_t *p_demux );
 116
 117 static int OpenAudioDev( demux_t *, const char * );
 118 static bool ProbeAudioDevAlsa( demux_t *, const char * );
 119 static char *ListAvailableDevices( demux_t *, bool b_probe );
 120
 121 struct demux_sys_t
 122 {
 123     /* Audio */
 124     int i_cache;
 125     unsigned int i_sample_rate;
 126     bool b_stereo;
 127     size_t i_max_frame_size;
 128     block_t *p_block;
 129     es_out_id_t *p_es;
 130
 131     /* ALSA Audio */
 132     snd_pcm_t *p_alsa_pcm;
 133     size_t i_alsa_frame_size;
 134     int i_alsa_chunk_size;
 135
 136     int64_t i_next_demux_date; /* Used to handle alsa:// as input-slave properly */
 137 };
 138
 139 static int FindMainDevice( demux_t *p_demux, const char *psz_device )
 140 {
 141     if( psz_device )
 142     {
 143         msg_Dbg( p_demux, "opening device '%s'", psz_device );
 144         if( ProbeAudioDevAlsa( p_demux, psz_device ) )
 145         {
 146             msg_Dbg( p_demux, "'%s' is an audio device", psz_device );
 147             OpenAudioDev( p_demux, psz_device );
 148         }
 149     }
 150     else if( ProbeAudioDevAlsa( p_demux, ALSA_DEFAULT ) )
 151     {
 152         msg_Dbg( p_demux, "'%s' is an audio device", ALSA_DEFAULT );
 153         OpenAudioDev( p_demux, ALSA_DEFAULT );
 154     }
 155     else if( ( psz_device = ListAvailableDevices( p_demux, true ) ) )
 156     {
 157         msg_Dbg( p_demux, "'%s' is an audio device", psz_device );
 158         OpenAudioDev( p_demux, psz_device );
 159         free( (char *)psz_device );
 160     }
 161
 162     if( p_demux->p_sys->p_alsa_pcm == NULL )
 163         return VLC_EGENERIC;
 164     return VLC_SUCCESS;
 165 }
 166
 167 static char *ListAvailableDevices( demux_t *p_demux, bool b_probe )
 168 {
 169     snd_ctl_card_info_t *p_info = NULL;
 170     snd_ctl_card_info_alloca( &p_info );
 171
 172     snd_pcm_info_t *p_pcminfo = NULL;
 173     snd_pcm_info_alloca( &p_pcminfo );
 174
 175     if( !b_probe )
 176         msg_Dbg( p_demux, "Available alsa capture devices:" );
 177     int i_card = -1;
 178     while( !snd_card_next( &i_card ) && i_card >= 0 )
 179     {
 180         char psz_devname[10];
 181         snprintf( psz_devname, 10, "hw:%d", i_card );
 182
 183         snd_ctl_t *p_ctl = NULL;
 184         if( snd_ctl_open( &p_ctl, psz_devname, 0 ) < 0 ) continue;
 185
 186         snd_ctl_card_info( p_ctl, p_info );
 187         if( !b_probe )
 188             msg_Dbg( p_demux, "  %s (%s)",
 189                      snd_ctl_card_info_get_id( p_info ),
 190                      snd_ctl_card_info_get_name( p_info ) );
 191
 192         int i_dev = -1;
 193         while( !snd_ctl_pcm_next_device( p_ctl, &i_dev ) && i_dev >= 0 )
 194         {
 195             snd_pcm_info_set_device( p_pcminfo, i_dev );
 196             snd_pcm_info_set_subdevice( p_pcminfo, 0 );
 197             snd_pcm_info_set_stream( p_pcminfo, SND_PCM_STREAM_CAPTURE );
 198             if( snd_ctl_pcm_info( p_ctl, p_pcminfo ) < 0 ) continue;
 199
 200             if( !b_probe )
 201                 msg_Dbg( p_demux, "    hw:%d,%d : %s (%s)", i_card, i_dev,
 202                          snd_pcm_info_get_id( p_pcminfo ),
 203                          snd_pcm_info_get_name( p_pcminfo ) );
 204             else
 205             {
 206                 char *psz_device;
 207                 if( asprintf( &psz_device, "hw:%d,%d", i_card, i_dev ) > 0 )
 208                 {
 209                     if( ProbeAudioDevAlsa( p_demux, psz_device ) )
 210                     {
 211                         snd_ctl_close( p_ctl );
 212                         return psz_device;
 213                     }
 214                     else
 215                         free( psz_device );
 216                 }
 217             }
 218         }
 219
 220         snd_ctl_close( p_ctl );
 221     }
 222     return NULL;
 223 }
 224
 225 /*****************************************************************************
 226  * DemuxOpen: opens alsa device, access_demux callback
 227  *****************************************************************************
 228  *
 229  * url: <alsa device>::::
 230  *
 231  *****************************************************************************/
 232 static int DemuxOpen( vlc_object_t *p_this )
 233 {
 234     demux_t     *p_demux = (demux_t*)p_this;
 235     demux_sys_t *p_sys;
 236
 237     /* Only when selected */
 238     if( *p_demux->psz_access == '\0' ) return VLC_EGENERIC;
 239
 240     /* Set up p_demux */
 241     p_demux->pf_control = DemuxControl;
 242     p_demux->pf_demux = Demux;
 243     p_demux->info.i_update = 0;
 244     p_demux->info.i_title = 0;
 245     p_demux->info.i_seekpoint = 0;
 246
 247     p_demux->p_sys = p_sys = calloc( 1, sizeof( demux_sys_t ) );
 248     if( p_sys == NULL ) return VLC_ENOMEM;
 249
 250     p_sys->i_sample_rate = var_InheritInteger( p_demux, CFG_PREFIX "samplerate" );
 251     p_sys->b_stereo = var_InheritBool( p_demux, CFG_PREFIX "stereo" );
 252     p_sys->i_cache = var_InheritInteger( p_demux, CFG_PREFIX "caching" );
 253     p_sys->p_es = NULL;
 254     p_sys->p_block = NULL;
 255     p_sys->i_next_demux_date = -1;
 256
 257     const char *psz_device = NULL;
 258     if( p_demux->psz_location && *p_demux->psz_location )
 259         psz_device = p_demux->psz_location;
 260     else
 261         ListAvailableDevices( p_demux, false );
 262
 263     if( FindMainDevice( p_demux, psz_device ) != VLC_SUCCESS )
 264     {
 265         if( p_demux->psz_location && *p_demux->psz_location )
 266             ListAvailableDevices( p_demux, false );
 267         DemuxClose( p_this );
 268         return VLC_EGENERIC;
 269     }
 270
 271     return VLC_SUCCESS;
 272 }
 273
 274 /*****************************************************************************
 275  * Close: close device, free resources
 276  *****************************************************************************/
 277 static void DemuxClose( vlc_object_t *p_this )
 278 {
 279     demux_t     *p_demux = (demux_t *)p_this;
 280     demux_sys_t *p_sys   = p_demux->p_sys;
 281
 282     if( p_sys->p_alsa_pcm )
 283     {
 284         snd_pcm_close( p_sys->p_alsa_pcm );
 285     }
 286
 287     if( p_sys->p_block ) block_Release( p_sys->p_block );
 288
 289     free( p_sys );
 290 }
 291
 292 /*****************************************************************************
 293  * DemuxControl:
 294  *****************************************************************************/
 295 static int DemuxControl( demux_t *p_demux, int i_query, va_list args )
 296 {
 297     demux_sys_t *p_sys = p_demux->p_sys;
 298
 299     switch( i_query )
 300     {
 301         /* Special for access_demux */
 302         case DEMUX_CAN_PAUSE:
 303         case DEMUX_CAN_SEEK:
 304         case DEMUX_SET_PAUSE_STATE:
 305         case DEMUX_CAN_CONTROL_PACE:
 306             *va_arg( args, bool * ) = false;
 307             return VLC_SUCCESS;
 308
 309         case DEMUX_GET_PTS_DELAY:
 310             *va_arg( args, int64_t * ) = (int64_t)p_sys->i_cache * 1000;
 311             return VLC_SUCCESS;
 312
 313         case DEMUX_GET_TIME:
 314             *va_arg( args, int64_t * ) = mdate();
 315             return VLC_SUCCESS;
 316
 317         case DEMUX_SET_NEXT_DEMUX_TIME:
 318             p_sys->i_next_demux_date = va_arg( args, int64_t );
 319             return VLC_SUCCESS;
 320
 321         /* TODO implement others */
 322         default:
 323             return VLC_EGENERIC;
 324     }
 325
 326     return VLC_EGENERIC;
 327 }
 328
 329 /*****************************************************************************
 330  * Demux: Processes the audio frame
 331  *****************************************************************************/
 332 static int Demux( demux_t *p_demux )
 333 {
 334     demux_sys_t *p_sys = p_demux->p_sys;
 335
 336     block_t *p_block = NULL;
 337
 338     do
 339     {
 340         if( p_block )
 341         {
 342             es_out_Send( p_demux->out, p_sys->p_es, p_block );
 343             p_block = NULL;
 344         }
 345
 346         /* Wait for data */
 347         int i_wait = snd_pcm_wait( p_sys->p_alsa_pcm, 10 ); /* See poll() comment in oss.c */
 348         switch( i_wait )
 349         {
 350             case 1:
 351             {
 352                 p_block = GrabAudio( p_demux );
 353                 if( p_block )
 354                     es_out_Control( p_demux->out, ES_OUT_SET_PCR, p_block->i_pts );
 355             }
 356
 357             /* FIXME: this is a copy paste from below. Shouldn't be needed
 358              * twice. */
 359             case -EPIPE:
 360                 /* xrun */
 361                 snd_pcm_prepare( p_sys->p_alsa_pcm );
 362                 break;
 363             case -ESTRPIPE:
 364             {
 365                 /* suspend */
 366                 int i_resume = snd_pcm_resume( p_sys->p_alsa_pcm );
 367                 if( i_resume < 0 && i_resume != -EAGAIN ) snd_pcm_prepare( p_sys->p_alsa_pcm );
 368                 break;
 369             }
 370             /* </FIXME> */
 371         }
 372     } while( p_block && p_sys->i_next_demux_date > 0 &&
 373              p_block->i_pts < p_sys->i_next_demux_date );
 374
 375     if( p_block )
 376         es_out_Send( p_demux->out, p_sys->p_es, p_block );
 377
 378     return 1;
 379 }
 380
 381
 382 /*****************************************************************************
 383  * GrabAudio: Grab an audio frame
 384  *****************************************************************************/
 385 static block_t* GrabAudio( demux_t *p_demux )
 386 {
 387     demux_sys_t *p_sys = p_demux->p_sys;
 388     int i_read, i_correct;
 389     block_t *p_block;
 390
 391     if( p_sys->p_block ) p_block = p_sys->p_block;
 392     else p_block = block_New( p_demux, p_sys->i_max_frame_size );
 393
 394     if( !p_block )
 395     {
 396         msg_Warn( p_demux, "cannot get block" );
 397         return 0;
 398     }
 399
 400     p_sys->p_block = p_block;
 401
 402     /* ALSA */
 403     i_read = snd_pcm_readi( p_sys->p_alsa_pcm, p_block->p_buffer, p_sys->i_alsa_chunk_size );
 404     if( i_read <= 0 )
 405     {
 406         int i_resume;
 407         switch( i_read )
 408         {
 409             case -EAGAIN:
 410                 break;
 411             case -EPIPE:
 412                 /* xrun */
 413                 snd_pcm_prepare( p_sys->p_alsa_pcm );
 414                 break;
 415             case -ESTRPIPE:
 416                 /* suspend */
 417                 i_resume = snd_pcm_resume( p_sys->p_alsa_pcm );
 418                 if( i_resume < 0 && i_resume != -EAGAIN ) snd_pcm_prepare( p_sys->p_alsa_pcm );
 419                 break;
 420             default:
 421                 msg_Err( p_demux, "Failed to read alsa frame (%s)", snd_strerror( i_read ) );
 422                 return 0;
 423         }
 424     }
 425     else
 426     {
 427         /* convert from frames to bytes */
 428         i_read *= p_sys->i_alsa_frame_size;
 429     }
 430
 431     if( i_read <= 0 ) return 0;
 432
 433     p_block->i_buffer = i_read;
 434     p_sys->p_block = 0;
 435
 436     /* Correct the date because of kernel buffering */
 437     i_correct = i_read;
 438     /* ALSA */
 439     int i_err;
 440     snd_pcm_sframes_t delay = 0;
 441     if( ( i_err = snd_pcm_delay( p_sys->p_alsa_pcm, &delay ) ) >= 0 )
 442     {
 443         size_t i_correction_delta = delay * p_sys->i_alsa_frame_size;
 444         /* Test for overrun */
 445         if( i_correction_delta > p_sys->i_max_frame_size )
 446         {
 447             msg_Warn( p_demux, "ALSA read overrun (%zu > %zu)",
 448                       i_correction_delta, p_sys->i_max_frame_size );
 449             i_correction_delta = p_sys->i_max_frame_size;
 450             snd_pcm_prepare( p_sys->p_alsa_pcm );
 451         }
 452         i_correct += i_correction_delta;
 453     }
 454     else
 455     {
 456         /* delay failed so reset */
 457         msg_Warn( p_demux, "ALSA snd_pcm_delay failed (%s)", snd_strerror( i_err ) );
 458         snd_pcm_prepare( p_sys->p_alsa_pcm );
 459     }
 460
 461     /* Timestamp */
 462     p_block->i_pts = p_block->i_dts =
 463         mdate() - INT64_C(1000000) * (mtime_t)i_correct /
 464         2 / ( p_sys->b_stereo ? 2 : 1) / p_sys->i_sample_rate;
 465
 466     return p_block;
 467 }
 468
 469 /*****************************************************************************
 470  * OpenAudioDev: open and set up the audio device and probe for capabilities
 471  *****************************************************************************/
 472 static int OpenAudioDevAlsa( demux_t *p_demux, const char *psz_device )
 473 {
 474     demux_sys_t *p_sys = p_demux->p_sys;
 475     p_sys->p_alsa_pcm = NULL;
 476     snd_pcm_hw_params_t *p_hw_params = NULL;
 477     snd_pcm_uframes_t buffer_size;
 478     snd_pcm_uframes_t chunk_size;
 479
 480     /* ALSA */
 481     int i_err;
 482
 483     if( ( i_err = snd_pcm_open( &p_sys->p_alsa_pcm, psz_device,
 484         SND_PCM_STREAM_CAPTURE, SND_PCM_NONBLOCK ) ) < 0)
 485     {
 486         msg_Err( p_demux, "Cannot open ALSA audio device %s (%s)",
 487                  psz_device, snd_strerror( i_err ) );
 488         goto adev_fail;
 489     }
 490
 491     if( ( i_err = snd_pcm_nonblock( p_sys->p_alsa_pcm, 1 ) ) < 0)
 492     {
 493         msg_Err( p_demux, "Cannot set ALSA nonblock (%s)",
 494                  snd_strerror( i_err ) );
 495         goto adev_fail;
 496     }
 497
 498     /* Begin setting hardware parameters */
 499
 500     if( ( i_err = snd_pcm_hw_params_malloc( &p_hw_params ) ) < 0 )
 501     {
 502         msg_Err( p_demux,
 503                  "ALSA: cannot allocate hardware parameter structure (%s)",
 504                  snd_strerror( i_err ) );
 505         goto adev_fail;
 506     }
 507
 508     if( ( i_err = snd_pcm_hw_params_any( p_sys->p_alsa_pcm, p_hw_params ) ) < 0 )
 509     {
 510         msg_Err( p_demux,
 511                 "ALSA: cannot initialize hardware parameter structure (%s)",
 512                  snd_strerror( i_err ) );
 513         goto adev_fail;
 514     }
 515
 516     /* Set Interleaved access */
 517     if( ( i_err = snd_pcm_hw_params_set_access( p_sys->p_alsa_pcm, p_hw_params, SND_PCM_ACCESS_RW_INTERLEAVED ) ) < 0 )
 518     {
 519         msg_Err( p_demux, "ALSA: cannot set access type (%s)",
 520                  snd_strerror( i_err ) );
 521         goto adev_fail;
 522     }
 523
 524     /* Set 16 bit little endian */
 525     if( ( i_err = snd_pcm_hw_params_set_format( p_sys->p_alsa_pcm, p_hw_params, SND_PCM_FORMAT_S16_LE ) ) < 0 )
 526     {
 527         msg_Err( p_demux, "ALSA: cannot set sample format (%s)",
 528                  snd_strerror( i_err ) );
 529         goto adev_fail;
 530     }
 531
 532     /* Set sample rate */
 533     i_err = snd_pcm_hw_params_set_rate_near( p_sys->p_alsa_pcm, p_hw_params, &p_sys->i_sample_rate, NULL );
 534     if( i_err < 0 )
 535     {
 536         msg_Err( p_demux, "ALSA: cannot set sample rate (%s)",
 537                  snd_strerror( i_err ) );
 538         goto adev_fail;
 539     }
 540
 541     /* Set channels */
 542     unsigned int channels = p_sys->b_stereo ? 2 : 1;
 543     if( ( i_err = snd_pcm_hw_params_set_channels( p_sys->p_alsa_pcm, p_hw_params, channels ) ) < 0 )
 544     {
 545         channels = ( channels==1 ) ? 2 : 1;
 546         msg_Warn( p_demux, "ALSA: cannot set channel count (%s). "
 547                   "Trying with channels=%d",
 548                   snd_strerror( i_err ),
 549                   channels );
 550         if( ( i_err = snd_pcm_hw_params_set_channels( p_sys->p_alsa_pcm, p_hw_params, channels ) ) < 0 )
 551         {
 552             msg_Err( p_demux, "ALSA: cannot set channel count (%s)",
 553                      snd_strerror( i_err ) );
 554             goto adev_fail;
 555         }
 556         p_sys->b_stereo = ( channels == 2 );
 557     }
 558
 559     /* Set metrics for buffer calculations later */
 560     unsigned int buffer_time;
 561     if( ( i_err = snd_pcm_hw_params_get_buffer_time_max(p_hw_params, &buffer_time, 0) ) < 0 )
 562     {
 563         msg_Err( p_demux, "ALSA: cannot get buffer time max (%s)",
 564                  snd_strerror( i_err ) );
 565         goto adev_fail;
 566     }
 567     if( buffer_time > 500000 ) buffer_time = 500000;
 568
 569     /* Set period time */
 570     unsigned int period_time = buffer_time / 4;
 571     i_err = snd_pcm_hw_params_set_period_time_near( p_sys->p_alsa_pcm, p_hw_params, &period_time, 0 );
 572     if( i_err < 0 )
 573     {
 574         msg_Err( p_demux, "ALSA: cannot set period time (%s)",
 575                  snd_strerror( i_err ) );
 576         goto adev_fail;
 577     }
 578
 579     /* Set buffer time */
 580     i_err = snd_pcm_hw_params_set_buffer_time_near( p_sys->p_alsa_pcm, p_hw_params, &buffer_time, 0 );
 581     if( i_err < 0 )
 582     {
 583         msg_Err( p_demux, "ALSA: cannot set buffer time (%s)",
 584                  snd_strerror( i_err ) );
 585         goto adev_fail;
 586     }
 587
 588     /* Apply new hardware parameters */
 589     if( ( i_err = snd_pcm_hw_params( p_sys->p_alsa_pcm, p_hw_params ) ) < 0 )
 590     {
 591         msg_Err( p_demux, "ALSA: cannot set hw parameters (%s)",
 592                  snd_strerror( i_err ) );
 593         goto adev_fail;
 594     }
 595
 596     /* Get various buffer metrics */
 597     snd_pcm_hw_params_get_period_size( p_hw_params, &chunk_size, 0 );
 598     snd_pcm_hw_params_get_buffer_size( p_hw_params, &buffer_size );
 599     if( chunk_size == buffer_size )
 600     {
 601         msg_Err( p_demux,
 602                  "ALSA: period cannot equal buffer size (%lu == %lu)",
 603                  chunk_size, buffer_size);
 604         goto adev_fail;
 605     }
 606
 607     int bits_per_sample = snd_pcm_format_physical_width(SND_PCM_FORMAT_S16_LE);
 608     int bits_per_frame = bits_per_sample * channels;
 609
 610     p_sys->i_alsa_chunk_size = chunk_size;
 611     p_sys->i_alsa_frame_size = bits_per_frame / 8;
 612     p_sys->i_max_frame_size = chunk_size * bits_per_frame / 8;
 613
 614     snd_pcm_hw_params_free( p_hw_params );
 615     p_hw_params = NULL;
 616
 617     /* Prep device */
 618     if( ( i_err = snd_pcm_prepare( p_sys->p_alsa_pcm ) ) < 0 )
 619     {
 620         msg_Err( p_demux,
 621                  "ALSA: cannot prepare audio interface for use (%s)",
 622                  snd_strerror( i_err ) );
 623         goto adev_fail;
 624     }
 625
 626     snd_pcm_start( p_sys->p_alsa_pcm );
 627
 628     return VLC_SUCCESS;
 629
 630  adev_fail:
 631
 632     if( p_hw_params ) snd_pcm_hw_params_free( p_hw_params );
 633     if( p_sys->p_alsa_pcm ) snd_pcm_close( p_sys->p_alsa_pcm );
 634     p_sys->p_alsa_pcm = NULL;
 635
 636     return VLC_EGENERIC;
 637
 638 }
 639
 640 static int OpenAudioDev( demux_t *p_demux, const char *psz_device )
 641 {
 642     demux_sys_t *p_sys = p_demux->p_sys;
 643     if( OpenAudioDevAlsa( p_demux, psz_device ) != VLC_SUCCESS )
 644         return VLC_EGENERIC;
 645
 646     msg_Dbg( p_demux, "opened adev=`%s' %s %dHz",
 647              psz_device, p_sys->b_stereo ? "stereo" : "mono",
 648              p_sys->i_sample_rate );
 649
 650     es_format_t fmt;
 651     es_format_Init( &fmt, AUDIO_ES, VLC_FOURCC('a','r','a','w') );
 652
 653     fmt.audio.i_channels = p_sys->b_stereo ? 2 : 1;
 654     fmt.audio.i_rate = p_sys->i_sample_rate;
 655     fmt.audio.i_bitspersample = 16;
 656     fmt.audio.i_blockalign = fmt.audio.i_channels * fmt.audio.i_bitspersample / 8;
 657     fmt.i_bitrate = fmt.audio.i_channels * fmt.audio.i_rate * fmt.audio.i_bitspersample;
 658
 659     msg_Dbg( p_demux, "new audio es %d channels %dHz",
 660              fmt.audio.i_channels, fmt.audio.i_rate );
 661
 662     p_sys->p_es = es_out_Add( p_demux->out, &fmt );
 663
 664     return VLC_SUCCESS;
 665 }
 666
 667 /*****************************************************************************
 668  * ProbeAudioDevAlsa: probe audio for capabilities
 669  *****************************************************************************/
 670 static bool ProbeAudioDevAlsa( demux_t *p_demux, const char *psz_device )
 671 {
 672     int i_err;
 673     snd_pcm_t *p_alsa_pcm;
 674
 675     if( ( i_err = snd_pcm_open( &p_alsa_pcm, psz_device, SND_PCM_STREAM_CAPTURE, SND_PCM_NONBLOCK ) ) < 0 )
 676     {
 677         msg_Err( p_demux, "cannot open device %s for ALSA audio (%s)", psz_device, snd_strerror( i_err ) );
 678         return false;
 679     }
 680
 681     snd_pcm_close( p_alsa_pcm );
 682
 683     return true;
 684 }