gstreamer/sys/v4l2/gstv4l2transform.c

/*
 * Copyright (C) 2014 Collabora Ltd.
 *     Author: Nicolas Dufresne <nicolas.dufresne@collabora.co.uk>
 *
 * 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., 51 Franklin St, Fifth Floor,
 * Boston, MA 02110-1301, USA.
 *
 */

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

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

#include "gstv4l2transform.h"
#include "v4l2_calls.h"

#include <string.h>
#include <gst/gst-i18n-plugin.h>

#define DEFAULT_PROP_DEVICE "/dev/video10"

#define V4L2_TRANSFORM_QUARK \
	g_quark_from_static_string("gst-v4l2-transform-info")

GST_DEBUG_CATEGORY_STATIC (gst_v4l2_transform_debug);
#define GST_CAT_DEFAULT gst_v4l2_transform_debug


enum
{
  PROP_0,
  V4L2_STD_OBJECT_PROPS,
  PROP_CAPTURE_IO_MODE,
};

typedef struct
{
  gchar *device;
  GstCaps *sink_caps;
  GstCaps *src_caps;
} GstV4l2TransformCData;

#define gst_v4l2_transform_parent_class parent_class
G_DEFINE_ABSTRACT_TYPE (GstV4l2Transform, gst_v4l2_transform,
    GST_TYPE_BASE_TRANSFORM);

static void
gst_v4l2_transform_set_property (GObject * object,
    guint prop_id, const GValue * value, GParamSpec * pspec)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (object);

  switch (prop_id) {
      /* Split IO mode so output is configure through 'io-mode' and capture
       * through 'capture-io-mode' */
    case PROP_IO_MODE:
      gst_v4l2_object_set_property_helper (self->v4l2output, prop_id, value,
          pspec);
      break;
    case PROP_CAPTURE_IO_MODE:
      gst_v4l2_object_set_property_helper (self->v4l2capture, PROP_IO_MODE,
          value, pspec);
      break;

    case PROP_DEVICE:
      gst_v4l2_object_set_property_helper (self->v4l2output, prop_id, value,
          pspec);
      gst_v4l2_object_set_property_helper (self->v4l2capture, prop_id, value,
          pspec);
      break;

      /* By default, only set on output */
    default:
      if (!gst_v4l2_object_set_property_helper (self->v4l2output,
              prop_id, value, pspec)) {
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      }
      break;
  }
}

static void
gst_v4l2_transform_get_property (GObject * object,
    guint prop_id, GValue * value, GParamSpec * pspec)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (object);

  switch (prop_id) {
    case PROP_IO_MODE:
      gst_v4l2_object_get_property_helper (self->v4l2output, prop_id, value,
          pspec);
      break;
    case PROP_CAPTURE_IO_MODE:
      gst_v4l2_object_get_property_helper (self->v4l2output, PROP_IO_MODE,
          value, pspec);
      break;

      /* By default read from output */
    default:
      if (!gst_v4l2_object_get_property_helper (self->v4l2output,
              prop_id, value, pspec)) {
        G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
      }
      break;
  }
}

static gboolean
gst_v4l2_transform_open (GstV4l2Transform * self)
{
  GST_DEBUG_OBJECT (self, "Opening");

  if (!gst_v4l2_object_open (self->v4l2output))
    goto failure;

  if (!gst_v4l2_object_open_shared (self->v4l2capture, self->v4l2output))
    goto failure;

  self->probed_sinkcaps = gst_v4l2_object_get_caps (self->v4l2output,
      gst_v4l2_object_get_raw_caps ());

  if (gst_caps_is_empty (self->probed_sinkcaps))
    goto no_input_format;

  self->probed_srccaps = gst_v4l2_object_get_caps (self->v4l2capture,
      gst_v4l2_object_get_raw_caps ());

  if (gst_caps_is_empty (self->probed_srccaps))
    goto no_output_format;

  return TRUE;

no_input_format:
  GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
      (_("Converter on device %s has no supported input format"),
          self->v4l2output->videodev), (NULL));
  goto failure;


no_output_format:
  GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
      (_("Converter on device %s has no supported output format"),
          self->v4l2output->videodev), (NULL));
  goto failure;

failure:
  if (GST_V4L2_IS_OPEN (self->v4l2output))
    gst_v4l2_object_close (self->v4l2output);

  if (GST_V4L2_IS_OPEN (self->v4l2capture))
    gst_v4l2_object_close (self->v4l2capture);

  gst_caps_replace (&self->probed_srccaps, NULL);
  gst_caps_replace (&self->probed_sinkcaps, NULL);

  return FALSE;
}

static void
gst_v4l2_transform_close (GstV4l2Transform * self)
{
  GST_DEBUG_OBJECT (self, "Closing");

  gst_v4l2_object_close (self->v4l2output);
  gst_v4l2_object_close (self->v4l2capture);

  gst_caps_replace (&self->probed_srccaps, NULL);
  gst_caps_replace (&self->probed_srccaps, NULL);
}

static gboolean
gst_v4l2_transform_stop (GstBaseTransform * trans)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);

  GST_DEBUG_OBJECT (self, "Stop");

  gst_v4l2_object_stop (self->v4l2output);
  gst_v4l2_object_stop (self->v4l2capture);
  gst_caps_replace (&self->incaps, NULL);
  gst_caps_replace (&self->outcaps, NULL);

  return TRUE;
}

static gboolean
gst_v4l2_transform_set_caps (GstBaseTransform * trans, GstCaps * incaps,
    GstCaps * outcaps)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);

  if (self->incaps && self->outcaps) {
    if (gst_caps_is_equal (incaps, self->incaps) &&
        gst_caps_is_equal (outcaps, self->outcaps)) {
      GST_DEBUG_OBJECT (trans, "Caps did not changed");
      return TRUE;
    }
  }

  /* TODO Add renegotiation support */
  g_return_val_if_fail (!GST_V4L2_IS_ACTIVE (self->v4l2output), FALSE);
  g_return_val_if_fail (!GST_V4L2_IS_ACTIVE (self->v4l2capture), FALSE);

  gst_caps_replace (&self->incaps, incaps);
  gst_caps_replace (&self->outcaps, outcaps);

  if (!gst_v4l2_object_set_format (self->v4l2output, incaps))
    goto incaps_failed;

  if (!gst_v4l2_object_set_format (self->v4l2capture, outcaps))
    goto outcaps_failed;

  /* FIXME implement fallback if crop not supported */
  if (!gst_v4l2_object_set_crop (self->v4l2output))
    goto failed;

  if (!gst_v4l2_object_set_crop (self->v4l2capture))
    goto failed;

  return TRUE;

incaps_failed:
  {
    GST_ERROR_OBJECT (self, "failed to set input caps: %" GST_PTR_FORMAT,
        incaps);
    goto failed;
  }
outcaps_failed:
  {
    gst_v4l2_object_stop (self->v4l2output);
    GST_ERROR_OBJECT (self, "failed to set output caps: %" GST_PTR_FORMAT,
        outcaps);
    goto failed;
  }
failed:
  return FALSE;
}

static gboolean
gst_v4l2_transform_query (GstBaseTransform * trans, GstPadDirection direction,
    GstQuery * query)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
  gboolean ret = TRUE;

  switch (GST_QUERY_TYPE (query)) {
    case GST_QUERY_CAPS:{
      GstCaps *filter, *caps = NULL, *result = NULL;
      GstPad *pad, *otherpad;

      gst_query_parse_caps (query, &filter);

      if (direction == GST_PAD_SRC) {
        pad = GST_BASE_TRANSFORM_SRC_PAD (trans);
        otherpad = GST_BASE_TRANSFORM_SINK_PAD (trans);
        if (self->probed_srccaps)
          caps = gst_caps_ref (self->probed_srccaps);
      } else {
        pad = GST_BASE_TRANSFORM_SINK_PAD (trans);
        otherpad = GST_BASE_TRANSFORM_SRC_PAD (trans);
        if (self->probed_srccaps)
          caps = gst_caps_ref (self->probed_sinkcaps);
      }

      if (!caps)
        caps = gst_pad_get_pad_template_caps (pad);

      if (filter) {
        GstCaps *tmp = caps;
        caps = gst_caps_intersect_full (filter, tmp, GST_CAPS_INTERSECT_FIRST);
        gst_caps_unref (tmp);
      }

      result = gst_pad_peer_query_caps (otherpad, caps);
      result = gst_caps_make_writable (result);
      gst_caps_append (result, caps);

      GST_DEBUG_OBJECT (self, "Returning %s caps %" GST_PTR_FORMAT,
          GST_PAD_NAME (pad), result);

      gst_query_set_caps_result (query, result);
      gst_caps_unref (result);
      break;
    }

    default:
      ret = GST_BASE_TRANSFORM_CLASS (parent_class)->query (trans, direction,
          query);
      break;
  }

  return ret;
}

static gboolean
gst_v4l2_transform_decide_allocation (GstBaseTransform * trans,
    GstQuery * query)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
  gboolean ret = FALSE;

  if (gst_v4l2_object_decide_allocation (self->v4l2capture, query)) {
    GstBufferPool *pool = GST_BUFFER_POOL (self->v4l2capture->pool);

    ret = GST_BASE_TRANSFORM_CLASS (parent_class)->decide_allocation (trans,
        query);

    if (!gst_buffer_pool_set_active (pool, TRUE))
      goto activate_failed;
  }

  return ret;

activate_failed:
  GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
      ("failed to activate bufferpool"), ("failed to activate bufferpool"));
  return TRUE;
}

static gboolean
gst_v4l2_transform_propose_allocation (GstBaseTransform * trans,
    GstQuery * decide_query, GstQuery * query)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
  gboolean ret = FALSE;

  if (decide_query == NULL)
    ret = TRUE;
  else
    ret = gst_v4l2_object_propose_allocation (self->v4l2output, query);

  if (ret)
    ret = GST_BASE_TRANSFORM_CLASS (parent_class)->propose_allocation (trans,
        decide_query, query);

  return ret;
}

/* copies the given caps */
static GstCaps *
gst_v4l2_transform_caps_remove_format_info (GstCaps * caps)
{
  GstStructure *st;
  GstCapsFeatures *f;
  gint i, n;
  GstCaps *res;

  res = gst_caps_new_empty ();

  n = gst_caps_get_size (caps);
  for (i = 0; i < n; i++) {
    st = gst_caps_get_structure (caps, i);
    f = gst_caps_get_features (caps, i);

    /* If this is already expressed by the existing caps
     * skip this structure */
    if (i > 0 && gst_caps_is_subset_structure_full (res, st, f))
      continue;

    st = gst_structure_copy (st);
    /* Only remove format info for the cases when we can actually convert */
    if (!gst_caps_features_is_any (f)
        && gst_caps_features_is_equal (f,
            GST_CAPS_FEATURES_MEMORY_SYSTEM_MEMORY))
      gst_structure_remove_fields (st, "format", "colorimetry", "chroma-site",
          NULL);

    gst_caps_append_structure_full (res, st, gst_caps_features_copy (f));
  }

  return res;
}

/* The caps can be transformed into any other caps with format info removed.
 * However, we should prefer passthrough, so if passthrough is possible,
 * put it first in the list. */
static GstCaps *
gst_v4l2_transform_transform_caps (GstBaseTransform * btrans,
    GstPadDirection direction, GstCaps * caps, GstCaps * filter)
{
  GstCaps *tmp, *tmp2;
  GstCaps *result;

  /* Get all possible caps that we can transform to */
  tmp = gst_v4l2_transform_caps_remove_format_info (caps);

  if (filter) {
    tmp2 = gst_caps_intersect_full (filter, tmp, GST_CAPS_INTERSECT_FIRST);
    gst_caps_unref (tmp);
    tmp = tmp2;
  }

  result = tmp;

  GST_DEBUG_OBJECT (btrans, "transformed %" GST_PTR_FORMAT " into %"
      GST_PTR_FORMAT, caps, result);

  return result;
}

static GstCaps *
gst_v4l2_transform_fixate_caps (GstBaseTransform * trans,
    GstPadDirection direction, GstCaps * caps, GstCaps * othercaps)
{
  GstCaps *result;

  GST_DEBUG_OBJECT (trans, "trying to fixate othercaps %" GST_PTR_FORMAT
      " based on caps %" GST_PTR_FORMAT, othercaps, caps);

  result = gst_caps_intersect (othercaps, caps);
  if (gst_caps_is_empty (result)) {
    gst_caps_unref (result);
    result = othercaps;
  } else {
    gst_caps_unref (othercaps);
  }

  GST_DEBUG_OBJECT (trans, "now fixating %" GST_PTR_FORMAT, result);

  result = gst_caps_fixate (result);

  return result;
}

static GstFlowReturn
gst_v4l2_transform_prepare_output_buffer (GstBaseTransform * trans,
    GstBuffer * inbuf, GstBuffer ** outbuf)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
  GstBufferPool *pool = GST_BUFFER_POOL (self->v4l2output->pool);
  GstFlowReturn ret = GST_FLOW_OK;
  GstBaseTransformClass *bclass = GST_BASE_TRANSFORM_CLASS (parent_class);

  if (gst_base_transform_is_passthrough (trans)) {
    GST_DEBUG_OBJECT (self, "Passthrough, no need to do anything");
    *outbuf = inbuf;
    goto beach;
  }

  /* Ensure input internal pool is active */
  if (!gst_buffer_pool_is_active (pool)) {
    GstStructure *config = gst_buffer_pool_get_config (pool);
    gst_buffer_pool_config_set_params (config, self->incaps,
        self->v4l2output->sizeimage, 2, 2);

    /* There is no reason to refuse this config */
    if (!gst_buffer_pool_set_config (pool, config))
      goto activate_failed;

    if (!gst_buffer_pool_set_active (pool, TRUE))
      goto activate_failed;
  }

  GST_DEBUG_OBJECT (self, "Queue input buffer");
  ret = gst_v4l2_buffer_pool_process (GST_V4L2_BUFFER_POOL (pool), inbuf);
  if (G_UNLIKELY (ret != GST_FLOW_OK))
    goto beach;

  pool = gst_base_transform_get_buffer_pool (trans);

  if (!gst_buffer_pool_set_active (pool, TRUE))
    goto activate_failed;

  GST_DEBUG_OBJECT (self, "Dequeue output buffer");
  ret = gst_buffer_pool_acquire_buffer (pool, outbuf, NULL);
  g_object_unref (pool);

  if (ret != GST_FLOW_OK)
    goto alloc_failed;

  pool = self->v4l2capture->pool;
  ret = gst_v4l2_buffer_pool_process (GST_V4L2_BUFFER_POOL (pool), *outbuf);

  if (ret != GST_FLOW_OK) {
    gst_buffer_unref (*outbuf);
    *outbuf = NULL;
  }

  if (bclass->copy_metadata)
    if (!bclass->copy_metadata (trans, inbuf, *outbuf)) {
      /* something failed, post a warning */
      GST_ELEMENT_WARNING (self, STREAM, NOT_IMPLEMENTED,
          ("could not copy metadata"), (NULL));
    }

beach:
  return ret;

activate_failed:
  GST_ELEMENT_ERROR (self, RESOURCE, SETTINGS,
      ("failed to activate bufferpool"), ("failed to activate bufferpool"));
  return GST_FLOW_ERROR;

alloc_failed:
  GST_DEBUG_OBJECT (self, "could not allocate buffer from pool");
  return ret;
}

static GstFlowReturn
gst_v4l2_transform_transform (GstBaseTransform * trans, GstBuffer * inbuf,
    GstBuffer * outbuf)
{
  /* Nothing to do */
  return GST_FLOW_OK;
}

static gboolean
gst_v4l2_transform_sink_event (GstBaseTransform * trans, GstEvent * event)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);

  switch (GST_EVENT_TYPE (event)) {
    case GST_EVENT_FLUSH_START:
      gst_v4l2_object_unlock (self->v4l2output);
      gst_v4l2_object_unlock (self->v4l2capture);
    default:
      break;
  }

  return GST_BASE_TRANSFORM_CLASS (parent_class)->sink_event (trans, event);
}

static GstStateChangeReturn
gst_v4l2_transform_change_state (GstElement * element,
    GstStateChange transition)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (element);
  GstStateChangeReturn ret;

  switch (transition) {
    case GST_STATE_CHANGE_NULL_TO_READY:
      if (!gst_v4l2_transform_open (self))
        return GST_STATE_CHANGE_FAILURE;
      break;
    case GST_STATE_CHANGE_PAUSED_TO_READY:
      gst_v4l2_object_unlock (self->v4l2output);
      gst_v4l2_object_unlock (self->v4l2capture);
      break;
    default:
      break;
  }

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

  switch (transition) {
    case GST_STATE_CHANGE_READY_TO_NULL:
      gst_v4l2_transform_close (self);
      break;
    default:
      break;
  }

  return ret;
}

static void
gst_v4l2_transform_dispose (GObject * object)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (object);

  gst_caps_replace (&self->probed_sinkcaps, NULL);
  gst_caps_replace (&self->probed_srccaps, NULL);

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

static void
gst_v4l2_transform_finalize (GObject * object)
{
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (object);

  gst_v4l2_object_destroy (self->v4l2capture);
  gst_v4l2_object_destroy (self->v4l2output);

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

static void
gst_v4l2_transform_init (GstV4l2Transform * self)
{
  /* V4L2 object are created in subinstance_init */
}

static void
gst_v4l2_transform_subinstance_init (GTypeInstance * instance, gpointer g_class)
{
  GstV4l2TransformClass *klass = GST_V4L2_TRANSFORM_CLASS (g_class);
  GstV4l2Transform *self = GST_V4L2_TRANSFORM (instance);

  self->v4l2output = gst_v4l2_object_new (GST_ELEMENT (self),
      V4L2_BUF_TYPE_VIDEO_OUTPUT, klass->default_device,
      gst_v4l2_get_output, gst_v4l2_set_output, NULL);
  self->v4l2output->no_initial_format = TRUE;
  self->v4l2output->keep_aspect = FALSE;

  self->v4l2capture = gst_v4l2_object_new (GST_ELEMENT (self),
      V4L2_BUF_TYPE_VIDEO_CAPTURE, klass->default_device,
      gst_v4l2_get_input, gst_v4l2_set_input, NULL);
  self->v4l2capture->no_initial_format = TRUE;
  self->v4l2output->keep_aspect = FALSE;

  g_object_set (self, "device", klass->default_device, NULL);
}

static void
gst_v4l2_transform_class_init (GstV4l2TransformClass * klass)
{
  GstElementClass *element_class;
  GObjectClass *gobject_class;
  GstBaseTransformClass *base_transform_class;

  element_class = (GstElementClass *) klass;
  gobject_class = (GObjectClass *) klass;
  base_transform_class = (GstBaseTransformClass *) klass;

  gst_element_class_set_static_metadata (element_class,
      "V4L2 Video Converter",
      "Filter/Converter/Video",
      "Transform streams via V4L2 API",
      "Nicolas Dufresne <nicolas.dufresne@collabora.com>");

  gobject_class->dispose = GST_DEBUG_FUNCPTR (gst_v4l2_transform_dispose);
  gobject_class->finalize = GST_DEBUG_FUNCPTR (gst_v4l2_transform_finalize);
  gobject_class->set_property =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_set_property);
  gobject_class->get_property =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_get_property);

  base_transform_class->stop = GST_DEBUG_FUNCPTR (gst_v4l2_transform_stop);
  base_transform_class->set_caps =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_set_caps);
  base_transform_class->query = GST_DEBUG_FUNCPTR (gst_v4l2_transform_query);
  base_transform_class->sink_event =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_sink_event);
  base_transform_class->decide_allocation =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_decide_allocation);
  base_transform_class->propose_allocation =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_propose_allocation);
  base_transform_class->transform_caps =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_transform_caps);
  base_transform_class->fixate_caps =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_fixate_caps);
  base_transform_class->prepare_output_buffer =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_prepare_output_buffer);
  base_transform_class->transform =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_transform);

  base_transform_class->passthrough_on_same_caps = TRUE;

  /* FIXME need this ? */
  element_class->change_state =
      GST_DEBUG_FUNCPTR (gst_v4l2_transform_change_state);

  gst_v4l2_object_install_properties_helper (gobject_class,
      DEFAULT_PROP_DEVICE);

  /**
   * GstV4l2Transform:capture-io-mode
   *
   * Capture IO Mode
   */
  g_object_class_install_property (gobject_class, PROP_CAPTURE_IO_MODE,
      g_param_spec_enum ("capture-io-mode", "Capture IO mode",
          "Capture I/O mode",
          GST_TYPE_V4L2_IO_MODE, GST_V4L2_IO_AUTO,
          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS));
}

static void
gst_v4l2_transform_subclass_init (gpointer g_class, gpointer data)
{
  GstV4l2TransformClass *klass = GST_V4L2_TRANSFORM_CLASS (g_class);
  GstElementClass *element_class = GST_ELEMENT_CLASS (g_class);
  GstV4l2TransformCData *cdata = data;

  klass->default_device = cdata->device;

  /* Note: gst_pad_template_new() take the floating ref from the caps */
  gst_element_class_add_pad_template (element_class,
      gst_pad_template_new ("sink", GST_PAD_SINK, GST_PAD_ALWAYS,
          cdata->sink_caps));
  gst_element_class_add_pad_template (element_class,
      gst_pad_template_new ("src", GST_PAD_SRC, GST_PAD_ALWAYS,
          cdata->src_caps));

  g_free (cdata);
}

/* Probing functions */
gboolean
gst_v4l2_is_transform (GstCaps * sink_caps, GstCaps * src_caps)
{
  gboolean ret = FALSE;

  if (gst_caps_is_subset (sink_caps, gst_v4l2_object_get_raw_caps ())
      && gst_caps_is_subset (src_caps, gst_v4l2_object_get_raw_caps ()))
    ret = TRUE;

  return ret;
}

gboolean
gst_v4l2_transform_register (GstPlugin * plugin, const gchar * basename,
    const gchar * device_path, GstCaps * sink_caps, GstCaps * src_caps)
{
  GTypeQuery type_query;
  GTypeInfo type_info = { 0, };
  GType type, subtype;
  gchar *type_name;
  GstV4l2TransformCData *cdata;

  cdata = g_new0 (GstV4l2TransformCData, 1);
  cdata->device = g_strdup (device_path);
  cdata->sink_caps = gst_caps_ref (sink_caps);
  cdata->src_caps = gst_caps_ref (src_caps);

  type = gst_v4l2_transform_get_type ();
  g_type_query (type, &type_query);
  memset (&type_info, 0, sizeof (type_info));
  type_info.class_size = type_query.class_size;
  type_info.instance_size = type_query.instance_size;
  type_info.class_init = gst_v4l2_transform_subclass_init;
  type_info.class_data = cdata;
  type_info.instance_init = gst_v4l2_transform_subinstance_init;

  type_name = g_strdup_printf ("v4l2%sconvert", basename);
  subtype = g_type_register_static (type, type_name, &type_info, 0);

  gst_element_register (plugin, type_name, GST_RANK_PRIMARY + 1, subtype);

  g_free (type_name);

  return TRUE;
}