static GstCaps *
gst_v4l2src_get_caps (GstBaseSrc * src, GstCaps * filter)
{
  GstV4l2Src *v4l2src;
  GstV4l2Object *obj;
  GstCaps *ret;
  GSList *walk;
  GSList *formats;

  v4l2src = GST_V4L2SRC (src);
  obj = v4l2src->v4l2object;

  if (!GST_V4L2_IS_OPEN (obj)) {
    return gst_pad_get_pad_template_caps (GST_BASE_SRC_PAD (v4l2src));
  }

  if (v4l2src->probed_caps)
    return gst_caps_ref (v4l2src->probed_caps);

  formats = gst_v4l2_object_get_format_list (obj);

  ret = gst_caps_new_empty ();

  for (walk = formats; walk; walk = walk->next) {
    struct v4l2_fmtdesc *format;
    GstStructure *template;

static gboolean
gst_v4l2src_set_caps (GstBaseSrc * src, GstCaps * caps)
{
  GstV4l2Src *v4l2src;
  GstV4l2Object *obj;

  v4l2src = GST_V4L2SRC (src);
  obj = v4l2src->v4l2object;

  /* make sure the caps changed before doing anything */
  if (gst_v4l2_object_caps_equal (obj, caps))
    return TRUE;

  /* make sure we stop capturing and dealloc buffers */
  if (!gst_v4l2_object_stop (obj))
    return FALSE;

  g_signal_emit (v4l2src, gst_v4l2_signals[SIGNAL_PRE_SET_FORMAT], 0,
      v4l2src->v4l2object->video_fd, caps);

  if (!gst_v4l2_object_set_format (obj, caps))
    /* error already posted */
    return FALSE;

  return TRUE;
}

static GstCaps *
gst_v4l2src_get_caps (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);
  GstCaps *ret;
  GSList *walk;
  GSList *formats;

  if (!GST_V4L2_IS_OPEN (v4l2src->v4l2object)) {
    /* FIXME: copy? */
    return
        gst_caps_copy (gst_pad_get_pad_template_caps (GST_BASE_SRC_PAD
            (v4l2src)));
  }

  if (v4l2src->probed_caps)
    return gst_caps_ref (v4l2src->probed_caps);

  formats = gst_v4l2_object_get_format_list (v4l2src->v4l2object);

  ret = gst_caps_new_empty ();

  for (walk = formats; walk; walk = walk->next) {
    struct v4l2_fmtdesc *format;

    GstStructure *template;

static gboolean
gst_v4l2src_iface_supported (GstImplementsInterface * iface, GType iface_type)
{
  GstV4l2Object *v4l2object = GST_V4L2SRC (iface)->v4l2object;

#ifdef HAVE_XVIDEO
  g_assert (iface_type == GST_TYPE_TUNER ||
      iface_type == GST_TYPE_X_OVERLAY ||
      iface_type == GST_TYPE_COLOR_BALANCE ||
      iface_type == GST_TYPE_VIDEO_ORIENTATION);
#else
  g_assert (iface_type == GST_TYPE_TUNER ||
      iface_type == GST_TYPE_COLOR_BALANCE ||
      iface_type == GST_TYPE_VIDEO_ORIENTATION);
#endif

  if (v4l2object->video_fd == -1)
    return FALSE;

#ifdef HAVE_XVIDEO
  if (iface_type == GST_TYPE_X_OVERLAY && !GST_V4L2_IS_OVERLAY (v4l2object))
    return FALSE;
#endif

  return TRUE;
}

static gboolean
gst_v4l2src_set_caps (GstBaseSrc * src, GstCaps * caps)
{
  GstV4l2Src *v4l2src;
  GstV4l2Object *obj;

  v4l2src = GST_V4L2SRC (src);
  obj = v4l2src->v4l2object;

  /* make sure the caps changed before doing anything */
  if (gst_v4l2_object_caps_equal (obj, caps))
    return TRUE;

  if (GST_V4L2_IS_ACTIVE (obj)) {
    /* Just check if the format is acceptable, once we know
     * no buffers should be outstanding we try S_FMT.
     *
     * Basesrc will do an allocation query that
     * should indirectly reclaim buffers, after that we can
     * set the format and then configure our pool */
    if (gst_v4l2_object_try_format (obj, caps)) {
      v4l2src->renegotiation_adjust = v4l2src->offset + 1;
      v4l2src->pending_set_fmt = TRUE;
    } else
      return FALSE;
  } else {
    /* make sure we stop capturing and dealloc buffers */
    if (!gst_v4l2_object_stop (obj))
      return FALSE;

    return gst_v4l2src_set_format (v4l2src, caps);
  }

  return TRUE;
}

static GstStateChangeReturn
gst_v4l2src_change_state (GstElement * element, GstStateChange transition)
{
  GstStateChangeReturn ret = GST_STATE_CHANGE_SUCCESS;
  GstV4l2Src *v4l2src = GST_V4L2SRC (element);
  GstV4l2Object *obj = v4l2src->v4l2object;

  switch (transition) {
    case GST_STATE_CHANGE_NULL_TO_READY:
      /* open the device */
      if (!gst_v4l2_object_open (obj))
        return GST_STATE_CHANGE_FAILURE;
      break;
    default:
      break;
  }

  ret = GST_ELEMENT_CLASS (parent_class)->change_state (element, transition);

  switch (transition) {
    case GST_STATE_CHANGE_READY_TO_NULL:
      /* close the device */
      if (!gst_v4l2_object_close (obj))
        return GST_STATE_CHANGE_FAILURE;

      break;
    default:
      break;
  }

  return ret;
}

static gboolean
gst_v4l2src_unlock_stop (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);

  v4l2src->last_timestamp = 0;

  return gst_v4l2_object_unlock_stop (v4l2src->v4l2object);
}

static void
gst_v4l2src_dispose (GObject * object)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (object);

  if (v4l2src->probed_caps) {
    gst_caps_unref (v4l2src->probed_caps);
  }

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

static gchar *
gst_v4l2src_uri_get_uri (GstURIHandler * handler)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (handler);

  if (v4l2src->v4l2object->videodev != NULL) {
    return g_strdup_printf ("v4l2://%s", v4l2src->v4l2object->videodev);
  }

  return g_strdup ("v4l2://");
}

static gboolean
gst_v4l2src_stop (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);
  GstV4l2Object *obj = v4l2src->v4l2object;

  if (GST_V4L2_IS_ACTIVE (obj)) {
    if (!gst_v4l2_object_stop (obj))
      return FALSE;
  }
  return TRUE;
}

/* start and stop are not symmetric -- start will open the device, but not start
 * capture. it's setcaps that will start capture, which is called via basesrc's
 * negotiate method. stop will both stop capture and close the device.
 */
static gboolean
gst_v4l2src_start (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);

  v4l2src->offset = 0;

  /* activate settings for first frame */
  v4l2src->ctrl_time = 0;
  gst_object_sync_values (GST_OBJECT (src), v4l2src->ctrl_time);

  return TRUE;
}

/* this is somewhat of a hack.. but better to keep the hack in
 * one place than copy/pasting it around..
 */
static GstV4l2Object *
get_v4l2_object (GstElement * v4l2elem)
{
  GstV4l2Object *v4l2object = NULL;
  if (GST_IS_V4L2SRC (v4l2elem)) {
    v4l2object = (GST_V4L2SRC (v4l2elem))->v4l2object;
  } else if (GST_IS_V4L2SINK (v4l2elem)) {
    v4l2object = (GST_V4L2SINK (v4l2elem))->v4l2object;
  } else {
    GST_ERROR_OBJECT (v4l2elem, "unknown v4l2 element");
  }
  return v4l2object;
}

static gboolean
gst_v4l2src_uri_set_uri (GstURIHandler * handler, const gchar * uri,
    GError ** error)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (handler);
  const gchar *device = DEFAULT_PROP_DEVICE;

  if (strcmp (uri, "v4l2://") != 0) {
    device = uri + 7;
  }
  g_object_set (v4l2src, "device", device, NULL);

  return TRUE;
}

static GstCaps *
gst_v4l2src_get_caps (GstBaseSrc * src, GstCaps * filter)
{
  GstV4l2Src *v4l2src;
  GstV4l2Object *obj;

  v4l2src = GST_V4L2SRC (src);
  obj = v4l2src->v4l2object;

  if (!GST_V4L2_IS_OPEN (obj)) {
    return gst_pad_get_pad_template_caps (GST_BASE_SRC_PAD (v4l2src));
  }

  return gst_v4l2_object_get_caps (obj, filter);
}

static void
gst_v4l2src_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (object);

  if (!gst_v4l2_object_get_property_helper (v4l2src->v4l2object,
          prop_id, value, pspec)) {
    switch (prop_id) {
      default:
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
        break;
    }
  }
}

/* start and stop are not symmetric -- start will open the device, but not start
 * capture. it's setcaps that will start capture, which is called via basesrc's
 * negotiate method. stop will both stop capture and close the device.
 */
static gboolean
gst_v4l2src_start (GstBaseSrc * src)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);

  v4l2src->offset = 0;
  v4l2src->renegotiation_adjust = 0;

  /* activate settings for first frame */
  v4l2src->ctrl_time = 0;
  gst_object_sync_values (GST_OBJECT (src), v4l2src->ctrl_time);

  v4l2src->has_bad_timestamp = FALSE;
  v4l2src->last_timestamp = 0;

  return TRUE;
}

static gboolean
gst_v4l2src_decide_allocation (GstBaseSrc * bsrc, GstQuery * query)
{
  GstV4l2Src *src = GST_V4L2SRC (bsrc);
  gboolean ret = TRUE;

  if (src->pending_set_fmt) {
    GstCaps *caps = gst_pad_get_current_caps (GST_BASE_SRC_PAD (bsrc));

    if (!gst_v4l2_object_stop (src->v4l2object))
      return FALSE;
    ret = gst_v4l2src_set_format (src, caps);
    gst_caps_unref (caps);
    src->pending_set_fmt = FALSE;
  }

  if (ret) {
    ret = gst_v4l2_object_decide_allocation (src->v4l2object, query);
    if (ret)
      ret = GST_BASE_SRC_CLASS (parent_class)->decide_allocation (bsrc, query);
  }

  if (ret) {
    if (!gst_buffer_pool_set_active (src->v4l2object->pool, TRUE))
      goto activate_failed;
  }

  return ret;

activate_failed:
  {
    GST_ELEMENT_ERROR (src, RESOURCE, SETTINGS,
        (_("Failed to allocate required memory.")),
        ("Buffer pool activation failed"));
    return FALSE;
  }
}

static gboolean
gst_v4l2src_decide_allocation (GstBaseSrc * bsrc, GstQuery * query)
{
  GstV4l2Src *src = GST_V4L2SRC (bsrc);
  gboolean ret = FALSE;

  if (gst_v4l2_object_decide_allocation (src->v4l2object, query))
    ret = GST_BASE_SRC_CLASS (parent_class)->decide_allocation (bsrc, query);

  if (ret) {
    if (!gst_buffer_pool_set_active (src->v4l2object->pool, TRUE))
      goto activate_failed;
  }

  return ret;

activate_failed:
  {
    GST_ELEMENT_ERROR (src, RESOURCE, SETTINGS,
        (_("Failed to allocate required memory.")),
        ("Buffer pool activation failed"));
    return FALSE;
  }
}

static gboolean
gst_v4l2src_decide_allocation (GstBaseSrc * bsrc, GstQuery * query)
{
  GstV4l2Src *src;
  GstV4l2Object *obj;
  GstBufferPool *pool;
  guint size, min, max;
  gboolean update;

  src = GST_V4L2SRC (bsrc);
  obj = src->v4l2object;

  if (gst_query_get_n_allocation_pools (query) > 0) {
    gst_query_parse_nth_allocation_pool (query, 0, &pool, &size, &min, &max);
    update = TRUE;
  } else {
    pool = NULL;
    min = max = 0;
    size = 0;
    update = FALSE;
  }

  GST_DEBUG_OBJECT (src, "allocation: size:%u min:%u max:%u pool:%"
      GST_PTR_FORMAT, size, min, max, pool);

  if (min != 0) {
    /* if there is a min-buffers suggestion, use it. We add 1 because we need 1
     * buffer extra to capture while the other two buffers are downstream */
    min += 1;
  } else {
    min = 2;
  }

  /* select a pool */
  switch (obj->mode) {
    case GST_V4L2_IO_RW:
      if (pool == NULL) {
        /* no downstream pool, use our own then */
        GST_DEBUG_OBJECT (src,
            "read/write mode: no downstream pool, using our own");
        pool = GST_BUFFER_POOL_CAST (obj->pool);
        size = obj->sizeimage;
      } else {
        /* in READ/WRITE mode, prefer a downstream pool because our own pool
         * doesn't help much, we have to write to it as well */
        GST_DEBUG_OBJECT (src, "read/write mode: using downstream pool");
        /* use the bigest size, when we use our own pool we can't really do any
         * other size than what the hardware gives us but for downstream pools
         * we can try */
        size = MAX (size, obj->sizeimage);
      }
      break;
    case GST_V4L2_IO_MMAP:
    case GST_V4L2_IO_USERPTR:
    case GST_V4L2_IO_DMABUF:
      /* in streaming mode, prefer our own pool */
      pool = GST_BUFFER_POOL_CAST (obj->pool);
      size = obj->sizeimage;
      GST_DEBUG_OBJECT (src,
          "streaming mode: using our own pool %" GST_PTR_FORMAT, pool);
      break;
    case GST_V4L2_IO_AUTO:
    default:
      GST_WARNING_OBJECT (src, "unhandled mode");
      break;
  }

  if (pool) {
    GstStructure *config;
    GstCaps *caps;

    config = gst_buffer_pool_get_config (pool);
    gst_buffer_pool_config_get_params (config, &caps, NULL, NULL, NULL);
    gst_buffer_pool_config_set_params (config, caps, size, min, max);

    /* if downstream supports video metadata, add this to the pool config */
    if (gst_query_find_allocation_meta (query, GST_VIDEO_META_API_TYPE, NULL)) {
      GST_DEBUG_OBJECT (pool, "activate Video Meta");
      gst_buffer_pool_config_add_option (config,
          GST_BUFFER_POOL_OPTION_VIDEO_META);
    }

    gst_buffer_pool_set_config (pool, config);
  }

  if (update)
    gst_query_set_nth_allocation_pool (query, 0, pool, size, min, max);
  else
    gst_query_add_allocation_pool (query, pool, size, min, max);

  return GST_BASE_SRC_CLASS (parent_class)->decide_allocation (bsrc, query);
}

static GstFlowReturn
gst_v4l2src_create (GstPushSrc * src, GstBuffer ** buf)
{
  GstV4l2Src *v4l2src = GST_V4L2SRC (src);
  GstV4l2Object *obj = v4l2src->v4l2object;
  GstV4l2BufferPool *pool = GST_V4L2_BUFFER_POOL_CAST (obj->pool);
  GstFlowReturn ret;
  GstClock *clock;
  GstClockTime abs_time, base_time, timestamp, duration;
  GstClockTime delay;

  do {
    ret = GST_BASE_SRC_CLASS (parent_class)->alloc (GST_BASE_SRC (src), 0,
        obj->info.size, buf);

    if (G_UNLIKELY (ret != GST_FLOW_OK))
      goto alloc_failed;

    ret = gst_v4l2_buffer_pool_process (pool, buf);

  } while (ret == GST_V4L2_FLOW_CORRUPTED_BUFFER);

  if (G_UNLIKELY (ret != GST_FLOW_OK))
    goto error;

  timestamp = GST_BUFFER_TIMESTAMP (*buf);
  duration = obj->duration;

  /* timestamps, LOCK to get clock and base time. */
  /* FIXME: element clock and base_time is rarely changing */
  GST_OBJECT_LOCK (v4l2src);
  if ((clock = GST_ELEMENT_CLOCK (v4l2src))) {
    /* we have a clock, get base time and ref clock */
    base_time = GST_ELEMENT (v4l2src)->base_time;
    gst_object_ref (clock);
  } else {
    /* no clock, can't set timestamps */
    base_time = GST_CLOCK_TIME_NONE;
  }
  GST_OBJECT_UNLOCK (v4l2src);

  /* sample pipeline clock */
  if (clock) {
    abs_time = gst_clock_get_time (clock);
    gst_object_unref (clock);
  } else {
    abs_time = GST_CLOCK_TIME_NONE;
  }

  if (timestamp != GST_CLOCK_TIME_NONE) {
    struct timespec now;
    GstClockTime gstnow;

    /* v4l2 specs say to use the system time although many drivers switched to
     * the more desirable monotonic time. We first try to use the monotonic time
     * and see how that goes */
    clock_gettime (CLOCK_MONOTONIC, &now);
    gstnow = GST_TIMESPEC_TO_TIME (now);

    if (gstnow < timestamp && (timestamp - gstnow) > (10 * GST_SECOND)) {
      GTimeVal now;

      /* very large diff, fall back to system time */
      g_get_current_time (&now);
      gstnow = GST_TIMEVAL_TO_TIME (now);
    }

    if (gstnow > timestamp) {
      delay = gstnow - timestamp;
    } else {
      delay = 0;
    }

    GST_DEBUG_OBJECT (v4l2src, "ts: %" GST_TIME_FORMAT " now %" GST_TIME_FORMAT
        " delay %" GST_TIME_FORMAT, GST_TIME_ARGS (timestamp),
        GST_TIME_ARGS (gstnow), GST_TIME_ARGS (delay));
  } else {
    /* we assume 1 frame latency otherwise */
    if (GST_CLOCK_TIME_IS_VALID (duration))
      delay = duration;
    else
      delay = 0;
  }

  /* set buffer metadata */
  GST_BUFFER_OFFSET (*buf) = v4l2src->offset++;
  GST_BUFFER_OFFSET_END (*buf) = v4l2src->offset;

  if (G_LIKELY (abs_time != GST_CLOCK_TIME_NONE)) {
    /* the time now is the time of the clock minus the base time */
    timestamp = abs_time - base_time;

    /* adjust for delay in the device */
    if (timestamp > delay)
      timestamp -= delay;
    else
      timestamp = 0;
  } else {
    timestamp = GST_CLOCK_TIME_NONE;
  }
//.........这里部分代码省略.........