gstreamer/sys/oss/gstosselement.c

/* GStreamer
 * Copyright (C) 1999,2000 Erik Walthinsen <omega@cse.ogi.edu>
 *                    2000 Wim Taymans <wim.taymans@chello.be>
 *
 * gstosssink.c: 
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Library General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library 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
 * Library General Public License for more details.
 *
 * You should have received a copy of the GNU Library General Public
 * License along with this library; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 02111-1307, USA.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <sys/types.h>
#include <sys/stat.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <sys/soundcard.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>

#include <gst/propertyprobe/propertyprobe.h>

#include "gstosselement.h"
#include "gstossmixer.h"

enum {
  ARG_0,
  ARG_DEVICE,
  ARG_MIXERDEV,
  ARG_DEVICE_NAME,
};

/* elementfactory information */
static GstElementDetails gst_osselement_details = GST_ELEMENT_DETAILS (
  "Audio Mixer (OSS)",
  "Generic/Audio",
  "OSS-based mixer element",
  "Ronald Bultje <rbultje@ronald.bitfreak.net>"
);

static void			gst_osselement_base_init	(GstOssElementClass *klass);
static void 			gst_osselement_class_init	(GstOssElementClass *klass);

static void			gst_ossprobe_interface_init	(GstPropertyProbeInterface *iface);
static void 			gst_osselement_init		(GstOssElement *oss);
static void 			gst_osselement_dispose		(GObject *object);

static void 			gst_osselement_set_property	(GObject *object,
								 guint prop_id, 
								 const GValue *value,
								 GParamSpec *pspec);
static void 			gst_osselement_get_property	(GObject *object,
								 guint prop_id,
								 GValue *value,
								 GParamSpec *pspec);
static GstElementStateReturn 	gst_osselement_change_state	(GstElement *element);

static GstElementClass *parent_class = NULL;
/*static guint gst_osssrc_signals[LAST_SIGNAL] = { 0 }; */

GType
gst_osselement_get_type (void) 
{
  static GType osselement_type = 0;

  if (!osselement_type) {
    static const GTypeInfo osselement_info = {
      sizeof(GstOssElementClass),
      (GBaseInitFunc)gst_osselement_base_init,
      NULL,
      (GClassInitFunc)gst_osselement_class_init,
      NULL,
      NULL,
      sizeof(GstOssElement),
      0,
      (GInstanceInitFunc)gst_osselement_init,
    };
    static const GInterfaceInfo ossiface_info = {
      (GInterfaceInitFunc) gst_oss_interface_init,
      NULL,
      NULL,
    };
    static const GInterfaceInfo ossmixer_info = {
      (GInterfaceInitFunc) gst_ossmixer_interface_init,
      NULL,
      NULL,
    };
    static const GInterfaceInfo ossprobe_info = {
      (GInterfaceInitFunc) gst_ossprobe_interface_init,
      NULL,
      NULL,
    };

    osselement_type = g_type_register_static (GST_TYPE_ELEMENT,
					      "GstOssElement",
					      &osselement_info, 0);
    g_type_add_interface_static (osselement_type,
				 GST_TYPE_IMPLEMENTS_INTERFACE,
				 &ossiface_info);
    g_type_add_interface_static (osselement_type,
				 GST_TYPE_MIXER,
				 &ossmixer_info);
    g_type_add_interface_static (osselement_type,
				 GST_TYPE_PROPERTY_PROBE,
				 &ossprobe_info);
  }

  return osselement_type;
}

static void
gst_osselement_base_init (GstOssElementClass *klass)
{
  GstElementClass *element_class = GST_ELEMENT_CLASS (klass);

  klass->device_combinations = NULL;

  gst_element_class_set_details (element_class, &gst_osselement_details);
}

static void
gst_osselement_class_init (GstOssElementClass *klass) 
{
  GObjectClass *gobject_class;
  GstElementClass *gstelement_class;

  gobject_class = (GObjectClass*)klass;
  gstelement_class = (GstElementClass*)klass;

  parent_class = g_type_class_ref (GST_TYPE_ELEMENT);

  g_object_class_install_property(G_OBJECT_CLASS(klass), ARG_DEVICE,
    g_param_spec_string ("device", "Device", "OSS device (/dev/dspN usually)",
                         "default", G_PARAM_READWRITE));
  g_object_class_install_property(G_OBJECT_CLASS(klass), ARG_MIXERDEV,
    g_param_spec_string ("mixerdev", "Mixer device",
			 "OSS mixer device (/dev/mixerN usually)",
                         "default", G_PARAM_READWRITE));
  g_object_class_install_property(G_OBJECT_CLASS(klass), ARG_DEVICE_NAME,
    g_param_spec_string ("device_name", "Device name", "Name of the device",
                         NULL, G_PARAM_READABLE));
  
  gobject_class->set_property = gst_osselement_set_property;
  gobject_class->get_property = gst_osselement_get_property;
  gobject_class->dispose      = gst_osselement_dispose;

  gstelement_class->change_state = gst_osselement_change_state;
}

static const GList *
gst_ossprobe_get_properties (GstPropertyProbe *probe)
{
  GObjectClass *klass = G_OBJECT_GET_CLASS (probe);
  static GList *list = NULL;

  if (!list) {
    list = g_list_append (NULL, g_object_class_find_property (klass, "device"));
  }

  return list;
}

static void
gst_osselement_probe (gchar  *device_base,
		      gint    device_num,
		      gchar **put)
{
  gchar *device;
  struct stat s;

  /* only if yet unfilled */
  if (*put != NULL)
    return;

  if (device_num == 0)
    device = g_strdup (device_base);
  else
    device = g_strdup_printf ("%s%d", device_base, device_num);

  if (lstat (device, &s) || !S_ISCHR (s.st_mode))
    goto end;

  *put = device;
  return;

end:
  g_free (device);
}

static gboolean
gst_osselement_class_probe_devices (GstOssElementClass *klass,
				    gboolean            check)
{
  static gboolean init = FALSE;
  static GList *device_combinations;

  if (!init && !check) {
    gchar *dsp_base[] = { "/dev/dsp", "/dev/sound/dsp", NULL };
    gchar *mixer_base[] = { "/dev/mixer", "/dev/sound/mixer", NULL };
    GstOssDeviceCombination devices[16];
    gint n;

    while (device_combinations) {
      GList *item = device_combinations;
      GstOssDeviceCombination *combi = item->data;

      device_combinations = g_list_remove (device_combinations, item);

      g_free (combi->dsp);
      g_free (combi->mixer);
      g_free (combi);
    }

    /* probe for all /dev entries */
    memset (devices, 0, sizeof (devices));

    /* OSS (without devfs) allows at max. 16 devices */
    for (n = 0; n < 16; n++) {
      gint base;

      for (base = 0; dsp_base[base] != NULL; base++)
        gst_osselement_probe (dsp_base[base], n, &devices[n].dsp);

      for (base = 0; mixer_base[base] != NULL; base++)
        gst_osselement_probe (mixer_base[base], n, &devices[n].mixer);
    }

    /* does the device exist (can we open them)? */
    for (n = 0; n < 16; n++) {
      gint fd;

      if (!devices[n].dsp)
        continue;

      /* we just check the dsp. we assume the mixer always works.
       * we don't need a mixer anyway (says OSS)... */
      if ((fd = open (devices[n].dsp, O_RDONLY)) > 0 || errno == EBUSY) {
        GstOssDeviceCombination *combi;

        if (fd > 0)
          close (fd);

        /* yay! \o/ */
        combi = g_new0 (GstOssDeviceCombination, 1);
        combi->dsp   = devices[n].dsp;
        combi->mixer = devices[n].mixer;
        devices[n].dsp = devices[n].mixer = NULL;

        device_combinations = g_list_append (device_combinations, combi);
      }
    }

    /* free */
    for (n = 0; n < 16; n++) {
      if (devices[n].dsp)
        g_free (devices[n].dsp);

      if (devices[n].mixer)
        g_free (devices[n].mixer);
    }

    init = TRUE;
  }

  klass->device_combinations = device_combinations;

  return init;
}

static GValueArray *
gst_osselement_class_list_devices (GstOssElementClass *klass)
{
  GValueArray *array;
  GValue value = { 0 };
  GList *item;

  if (!klass->device_combinations)
    return NULL;

  array = g_value_array_new (g_list_length (klass->device_combinations));
  item = klass->device_combinations;
  g_value_init (&value, G_TYPE_STRING);
  while (item) {
    GstOssDeviceCombination *combi = item->data;

    g_value_set_string (&value, combi->dsp);
    g_value_array_append (array, &value);

    item = item->next;
  }
  g_value_unset (&value);

  return array;
}

static void
gst_ossprobe_probe_property (GstPropertyProbe *probe,
			     guint             prop_id,
			     const GParamSpec *pspec)
{
  GstOssElementClass *klass = GST_OSSELEMENT_GET_CLASS (probe);

  switch (prop_id) {
    case ARG_DEVICE:
      gst_osselement_class_probe_devices (klass, FALSE);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (probe, prop_id, pspec);
      break;
  }
}

static gboolean
gst_ossprobe_needs_probe (GstPropertyProbe *probe,
			  guint             prop_id,
			  const GParamSpec *pspec)
{
  GstOssElementClass *klass = GST_OSSELEMENT_GET_CLASS (probe);
  gboolean ret = FALSE;

  switch (prop_id) {
    case ARG_DEVICE:
      ret = !gst_osselement_class_probe_devices (klass, TRUE);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (probe, prop_id, pspec);
      break;
  }

  return ret;
}

static GValueArray *
gst_ossprobe_get_values (GstPropertyProbe *probe,
			 guint             prop_id,
			 const GParamSpec *pspec)
{
  GstOssElementClass *klass = GST_OSSELEMENT_GET_CLASS (probe);
  GValueArray *array = NULL;

  switch (prop_id) {
    case ARG_DEVICE:
      array = gst_osselement_class_list_devices (klass);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (probe, prop_id, pspec);
      break;
  }

  return array;
}

static void
gst_ossprobe_interface_init (GstPropertyProbeInterface *iface)
{
  iface->get_properties = gst_ossprobe_get_properties;
  iface->probe_property = gst_ossprobe_probe_property;
  iface->needs_probe    = gst_ossprobe_needs_probe;
  iface->get_values     = gst_ossprobe_get_values;
}

static void 
gst_osselement_init (GstOssElement *oss) 
{
  oss->device = g_strdup ("/dev/dsp");
  oss->mixer_dev = g_strdup ("/dev/mixer");
  oss->fd = -1;
  oss->mixer_fd = -1;
  oss->tracklist = NULL;
  oss->device_name = NULL;

  gst_osselement_reset (oss);
}

static void
gst_osselement_dispose (GObject *object)
{
  GstOssElement *oss = (GstOssElement *) object;

  g_free (oss->device);
  g_free (oss->mixer_dev);

  G_OBJECT_CLASS (parent_class)->dispose (object);
}

void 
gst_osselement_reset (GstOssElement *oss) 
{
  oss->law = 0;
  oss->endianness = G_BYTE_ORDER;
  oss->sign = TRUE;
  oss->width = 16;
  oss->depth = 16;
  oss->channels = 2;
  oss->rate = 44100;
  oss->fragment = 6;
  oss->bps = 0;

/* AFMT_*_BE not available on all OSS includes (e.g. FBSD) */
#ifdef WORDS_BIGENDIAN
  oss->format = AFMT_S16_BE;
#else
  oss->format = AFMT_S16_LE;
#endif /* WORDS_BIGENDIAN */  
}

static gboolean 
gst_ossformat_get (gint law, gint endianness, gboolean sign, gint width, gint depth,
		   gint *format, gint *bps) 
{
  if (width != depth) 
    return FALSE;

  *bps = 1;

  if (law == 0) {
    if (width == 16) {
      if (sign == TRUE) {
        if (endianness == G_LITTLE_ENDIAN) {
	  *format = AFMT_S16_LE;
	  GST_DEBUG (
	             "16 bit signed LE, no law (%d)", *format);
	}
        else if (endianness == G_BIG_ENDIAN) {
	  *format = AFMT_S16_BE;
	  GST_DEBUG (
	             "16 bit signed BE, no law (%d)", *format);
	}
      }
      else {
        if (endianness == G_LITTLE_ENDIAN) {
	  *format = AFMT_U16_LE;
	  GST_DEBUG (
	             "16 bit unsigned LE, no law (%d)", *format);
	}
        else if (endianness == G_BIG_ENDIAN) {
	  *format = AFMT_U16_BE;
	  GST_DEBUG (
	             "16 bit unsigned BE, no law (%d)", *format);
	}
      }
      *bps = 2;
    }
    else if (width == 8) {
      if (sign == TRUE) {
	*format = AFMT_S8;
	GST_DEBUG (
	           "8 bit signed, no law (%d)", *format);
      }
      else {
        *format = AFMT_U8;
	GST_DEBUG (
	           "8 bit unsigned, no law (%d)", *format);
      }
      *bps = 1;
    }
  } else if (law == 1) {
    *format = AFMT_MU_LAW;
    GST_DEBUG (
	       "mu law (%d)", *format);
  } else if (law == 2) {
    *format = AFMT_A_LAW;
    GST_DEBUG (
	       "a law (%d)", *format);
  } else {
    g_critical ("unknown law");
    return FALSE;
  }

  return TRUE;
}

gboolean 
gst_osselement_parse_caps (GstOssElement *oss, const GstCaps *caps) 
{
  gint bps, format;
  GstStructure *structure;

  structure = gst_caps_get_structure (caps, 0);

  gst_structure_get_int  (structure, "width", &oss->width);
  gst_structure_get_int  (structure, "depth", &oss->depth);
	        
  if (oss->width != oss->depth) 
    return FALSE;
		  
  gst_structure_get_int  (structure, "law", &oss->law); 
  gst_structure_get_int  (structure, "endianness", &oss->endianness);
  gst_structure_get_boolean  (structure, "signed", &oss->sign);
			    
  if (!gst_ossformat_get (oss->law, oss->endianness, oss->sign, 
                          oss->width, oss->depth, &format, &bps))
  { 
     GST_DEBUG ("could not get format");
     return FALSE;
  }

  gst_structure_get_int  (structure, "channels", &oss->channels);
  gst_structure_get_int  (structure, "rate", &oss->rate);
			      
  oss->bps = bps * oss->channels * oss->rate;
  oss->format = format;

  return TRUE;
}

#define GET_FIXED_INT(caps, name, dest)         \
G_STMT_START {                                  \
  if (gst_caps_has_fixed_property (caps, name)) \
    gst_structure_get_int  (structure, name, dest);        \
} G_STMT_END
#define GET_FIXED_BOOLEAN(caps, name, dest)     \
G_STMT_START {                                  \
  if (gst_caps_has_fixed_property (caps, name)) \
    gst_structure_get_boolean  (structure, name, dest);    \
} G_STMT_END

gboolean 
gst_osselement_merge_fixed_caps (GstOssElement *oss, GstCaps *caps) 
{
  gint bps, format;
  GstStructure *structure;

  structure = gst_caps_get_structure (caps, 0);
  
  /* peel off fixed stuff from the caps */
  gst_structure_get_int (structure, "law",        &oss->law);
  gst_structure_get_int (structure, "endianness", &oss->endianness);
  gst_structure_get_boolean (structure, "signed",     &oss->sign);
  gst_structure_get_int (structure, "width",      &oss->width);
  gst_structure_get_int (structure, "depth",      &oss->depth);

  if (!gst_ossformat_get (oss->law, oss->endianness, oss->sign, 
                          oss->width, oss->depth, &format, &bps))
  { 
     return FALSE;
  }

  gst_structure_get_int (structure, "rate",       &oss->rate);
  gst_structure_get_int (structure, "channels",   &oss->channels);
			      
  oss->bps = bps * oss->channels * oss->rate;
  oss->format = format;
					  
  return TRUE;
}

gboolean 
gst_osselement_sync_parms (GstOssElement *oss) 
{
  audio_buf_info space;
  int frag;
  gint target_format;
  gint target_channels;
  gint target_rate;
  gint fragscale, frag_ln;

  if (oss->fd == -1)
    return FALSE;
  
  if (oss->fragment >> 16)
    frag = oss->fragment;
  else
    frag = 0x7FFF0000 | oss->fragment;
  
  GST_INFO ("osselement: setting sound card to %dHz %d format %s (%08x fragment)",
            oss->rate, oss->format,
            (oss->channels == 2) ? "stereo" : "mono", frag);

  ioctl (oss->fd, SNDCTL_DSP_SETFRAGMENT, &frag);
  ioctl (oss->fd, SNDCTL_DSP_RESET, 0);

  target_format   = oss->format;
  target_channels = oss->channels;
  target_rate     = oss->rate;

  ioctl (oss->fd, SNDCTL_DSP_SETFMT,   &oss->format);
  ioctl (oss->fd, SNDCTL_DSP_CHANNELS, &oss->channels);
  ioctl (oss->fd, SNDCTL_DSP_SPEED,    &oss->rate);

  ioctl (oss->fd, SNDCTL_DSP_GETBLKSIZE, &oss->fragment_size);

  if (oss->mode == GST_OSSELEMENT_WRITE) {
    ioctl (oss->fd, SNDCTL_DSP_GETOSPACE, &space);
  }
  else {
    ioctl (oss->fd, SNDCTL_DSP_GETISPACE, &space);
  }

  /* calculate new fragment using a poor man's logarithm function */
  fragscale = 1;
  frag_ln = 0;
  while (fragscale < space.fragsize) {
    fragscale <<= 1;
    frag_ln++;
  }
  oss->fragment = space.fragstotal << 16 | frag_ln;
	  
  GST_INFO ("osselement: set sound card to %dHz, %d format, %s "
	    "(%d bytes buffer, %08x fragment)",
            oss->rate, oss->format,
            (oss->channels == 2) ? "stereo" : "mono", 
	    space.bytes, oss->fragment);

  oss->fragment_time = (GST_SECOND * oss->fragment_size) / oss->bps;
  GST_INFO ("fragment time %u %" G_GUINT64_FORMAT "\n", 
            oss->bps, oss->fragment_time);

  if (target_format   != oss->format   ||
      target_channels != oss->channels ||
      target_rate     != oss->rate) 
  {
    g_warning ("couldn't set requested OSS parameters, enjoy the noise :)");
    /* we could eventually return FALSE here, or just do some additional tests
     * to see that the frequencies don't differ too much etc.. */
  }
  return TRUE;
}

static gboolean
gst_osselement_open_audio (GstOssElement *oss)
{
  gint caps;
  GstOssOpenMode mode = GST_OSSELEMENT_READ;
  const GList *padlist;

  g_return_val_if_fail (oss->fd == -1, FALSE);
  GST_INFO ("osselement: attempting to open sound device");

  /* Ok, so how do we open the device? We assume that we have (max.) one
   * pad, and if this is a sinkpad, we're osssink (w). else, we're osssrc (r) */
  padlist = gst_element_get_pad_list (GST_ELEMENT (oss));
  if (padlist != NULL) {
    GstPad *firstpad = padlist->data;
    if (GST_PAD_IS_SINK (firstpad)) {
      mode = GST_OSSELEMENT_WRITE;
    }
  } else {
    goto do_mixer;
  }

  /* first try to open the sound card */
  if (mode == GST_OSSELEMENT_WRITE) {
    /* open non blocking first so that it returns immediatly with an error
     * when we cannot get to the device */
    oss->fd = open (oss->device, O_WRONLY | O_NONBLOCK);

    if (oss->fd >= 0) {
      close (oss->fd);
			  
      /* re-open the sound device in blocking mode */
      oss->fd = open (oss->device, O_WRONLY);
    }
  }
  else {
    oss->fd = open (oss->device, O_RDONLY);
  }

  if (oss->fd < 0) {
    switch (errno) {
      case EBUSY:
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Unable to open %s (in use ?)",
			   oss->device);
	break;
      case EISDIR:
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Device %s is a directory",
			   oss->device);
	break;
      case EACCES:
      case ETXTBSY:
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Cannot access %s, check permissions",
			   oss->device);
	break;
      case ENXIO:
      case ENODEV:
      case ENOENT:
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Cannot access %s, does it exist ?",
			   oss->device);
	break;
      case EROFS:
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Cannot access %s, read-only filesystem ?",
			   oss->device);
      default:
	/* FIXME: strerror is not threadsafe */
	gst_element_error (GST_ELEMENT (oss),
			   "osselement: Cannot open %s, generic error: %s",
			   oss->device, strerror (errno));
	break;
    }
    return FALSE;
  }

  oss->mode = mode;

  /* we have it, set the default parameters and go have fun */
  /* set card state */
  ioctl (oss->fd, SNDCTL_DSP_GETCAPS, &caps);

  GST_INFO ("osselement: Capabilities %08x", caps);

  if (caps & DSP_CAP_DUPLEX)	GST_INFO ( "osselement:   Full duplex");
  if (caps & DSP_CAP_REALTIME) 	GST_INFO ( "osselement:   Realtime");
  if (caps & DSP_CAP_BATCH)    	GST_INFO ( "osselement:   Batch");
  if (caps & DSP_CAP_COPROC)   	GST_INFO ( "osselement:   Has coprocessor");
  if (caps & DSP_CAP_TRIGGER)  	GST_INFO ( "osselement:   Trigger");
  if (caps & DSP_CAP_MMAP)     	GST_INFO ( "osselement:   Direct access");

#ifdef DSP_CAP_MULTI
  if (caps & DSP_CAP_MULTI)    	GST_INFO ( "osselement:   Multiple open");
#endif /* DSP_CAP_MULTI */

#ifdef DSP_CAP_BIND
  if (caps & DSP_CAP_BIND)     	GST_INFO ( "osselement:   Channel binding");
#endif /* DSP_CAP_BIND */

  ioctl(oss->fd, SNDCTL_DSP_GETFMTS, &caps);

  GST_INFO ( "osselement: Formats %08x", caps);
  if (caps & AFMT_MU_LAW)  	GST_INFO ( "osselement:   MU_LAW");
  if (caps & AFMT_A_LAW)    	GST_INFO ( "osselement:   A_LAW");
  if (caps & AFMT_IMA_ADPCM)   	GST_INFO ( "osselement:   IMA_ADPCM");
  if (caps & AFMT_U8)    	GST_INFO ( "osselement:   U8");
  if (caps & AFMT_S16_LE)    	GST_INFO ( "osselement:   S16_LE");
  if (caps & AFMT_S16_BE)    	GST_INFO ( "osselement:   S16_BE");
  if (caps & AFMT_S8)    	GST_INFO ( "osselement:   S8");
  if (caps & AFMT_U16_LE)       GST_INFO ( "osselement:   U16_LE");
  if (caps & AFMT_U16_BE)    	GST_INFO ( "osselement:   U16_BE");
  if (caps & AFMT_MPEG)    	GST_INFO ( "osselement:   MPEG");
#ifdef AFMT_AC3
  if (caps & AFMT_AC3)    	GST_INFO ( "osselement:   AC3");
#endif

  GST_INFO ("osselement: opened audio (%s) with fd=%d",
	    oss->device, oss->fd);

  oss->caps = caps;

do_mixer:
  gst_ossmixer_build_list (oss);

  return TRUE;
}

static void
gst_osselement_close_audio (GstOssElement *oss)
{
  gst_ossmixer_free_list (oss);

  if (oss->fd < 0) 
    return;

  close(oss->fd);
  oss->fd = -1;
}

gboolean
gst_osselement_convert (GstOssElement *oss,
			GstFormat      src_format,
			gint64         src_value,
	        	GstFormat     *dest_format,
			gint64        *dest_value)
{
  gboolean res = TRUE;

  if (src_format == *dest_format) {
    *dest_value = src_value;
    return TRUE;
  }

  if (oss->bps == 0 || oss->channels == 0 || oss->width == 0)
    return FALSE;

  switch (src_format) {
    case GST_FORMAT_BYTES:
      switch (*dest_format) {
        case GST_FORMAT_TIME:
	  *dest_value = src_value * GST_SECOND / oss->bps;
          break;
        case GST_FORMAT_DEFAULT:
	  *dest_value = src_value / (oss->width * oss->channels / 8);
          break;
        default:
          res = FALSE;
      }
      break;
    case GST_FORMAT_TIME:
      switch (*dest_format) {
        case GST_FORMAT_BYTES:
	  *dest_value = src_value * oss->bps / GST_SECOND;
          break;
        case GST_FORMAT_DEFAULT:
	  *dest_value = src_value * oss->rate / GST_SECOND;
          break;
        default:
          res = FALSE;
      }
      break;
    case GST_FORMAT_DEFAULT:
      switch (*dest_format) {
        case GST_FORMAT_TIME:
	  *dest_value = src_value * GST_SECOND / oss->rate;
          break;
        case GST_FORMAT_BYTES:
	  *dest_value = src_value * oss->width * oss->channels / 8;
          break;
        default:
          res = FALSE;
      }
      break;
    default:
      res = FALSE;
  }

  return res;
}

static void 
gst_osselement_set_property (GObject *object,
			     guint prop_id,
			     const GValue *value,
			     GParamSpec *pspec) 
{
  GstOssElement *oss = GST_OSSELEMENT (object);

  switch (prop_id) {
    case ARG_DEVICE:
      /* disallow changing the device while it is opened
         get_property("device") should return the right one */
      if (gst_element_get_state (GST_ELEMENT (oss)) == GST_STATE_NULL) {
        g_free (oss->device);
        oss->device = g_strdup (g_value_get_string (value));

        /* let's assume that if we have a device map for the mixer,
	 * we're allowed to do all that automagically here */
        if (GST_OSSELEMENT_GET_CLASS (oss)->device_combinations != NULL) {
          GList *list = GST_OSSELEMENT_GET_CLASS (oss)->device_combinations;

          while (list) {
            GstOssDeviceCombination *combi = list->data;

            if (!strcmp (combi->dsp, oss->device)) {
              g_free (oss->mixer_dev);
              oss->mixer_dev = g_strdup (combi->mixer);
              break;
            }

            list = list->next;
          }
        }
      }
      break;
    case ARG_MIXERDEV:
      /* disallow changing the device while it is opened
         get_property("mixerdev") should return the right one */
      if (gst_element_get_state (GST_ELEMENT (oss)) == GST_STATE_NULL) {
        g_free (oss->mixer_dev);
        oss->mixer_dev = g_strdup (g_value_get_string (value));
      }
      break;
    default:
      break;
  }
}

static void 
gst_osselement_get_property (GObject *object,
			     guint prop_id,
			     GValue *value,
			     GParamSpec *pspec) 
{
  GstOssElement *oss = GST_OSSELEMENT (object);

  switch (prop_id) {
    case ARG_DEVICE:
      g_value_set_string (value, oss->device);
      break;
    case ARG_MIXERDEV:
      g_value_set_string (value, oss->mixer_dev);
      break;
    case ARG_DEVICE_NAME:
      g_value_set_string (value, oss->device_name);
      break;
    default:
      G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      break;
  }
}

static GstElementStateReturn 
gst_osselement_change_state (GstElement *element) 
{
  GstOssElement *oss = GST_OSSELEMENT (element);

  switch (GST_STATE_TRANSITION (element)) {
    case GST_STATE_NULL_TO_READY:
      if (!gst_osselement_open_audio (oss)) {
        return GST_STATE_FAILURE;
      }
      GST_INFO ("osselement: opened sound device");
      break;
    case GST_STATE_READY_TO_NULL:
      gst_osselement_close_audio (oss);
      gst_osselement_reset (oss);
      GST_INFO ("osselement: closed sound device");
      break;
    default:
      break;
  }
      
  if (GST_ELEMENT_CLASS (parent_class)->change_state)
    return GST_ELEMENT_CLASS (parent_class)->change_state (element);

  return GST_STATE_SUCCESS;
}