Implement GstV4l2Transform

Implement a v4l2 element that wraps HW video converters.

5 files changed, 767 insertions, 0 deletions

diff --git a/sys/v4l2/Makefile.am b/sys/v4l2/Makefile.am
index 248605fb7..1afed3219 100644
--- a/sys/v4l2/Makefile.am
+++ b/sys/v4l2/Makefile.am
@@ -11,6 +11,7 @@ libgstvideo4linux2_la_SOURCES = gstv4l2.c \
 				gstv4l2src.c \
 				gstv4l2radio.c \
 				gstv4l2tuner.c \
+				gstv4l2transform.c \
 				gstv4l2videodec.c \
 				gstv4l2vidorient.c \
 				v4l2_calls.c \
@@ -50,6 +51,7 @@ noinst_HEADERS = \
 	gstv4l2src.h \
 	gstv4l2radio.h \
 	gstv4l2tuner.h \
+	gstv4l2transform.h \
 	gstv4l2videodec.h \
 	gstv4l2vidorient.h \
 	v4l2_calls.h \
diff --git a/sys/v4l2/gstv4l2.c b/sys/v4l2/gstv4l2.c
index fc36d185c..db1052dd5 100644
--- a/sys/v4l2/gstv4l2.c
+++ b/sys/v4l2/gstv4l2.c
@@ -44,6 +44,7 @@
 #include "gstv4l2radio.h"
 #include "gstv4l2videodec.h"
 #include "gstv4l2devicemonitor.h"
+#include "gstv4l2transform.h"
 
 /* used in v4l2_calls.c and v4l2src_calls.c */
 GST_DEBUG_CATEGORY (v4l2_debug);
@@ -148,6 +149,9 @@ gst_v4l2_probe_and_register (GstPlugin * plugin)
     if (gst_v4l2_is_video_dec (sink_caps, src_caps))
       ret = gst_v4l2_video_dec_register (plugin, basename, it->device_path,
           sink_caps, src_caps);
+    else if (gst_v4l2_is_transform (sink_caps, src_caps))
+      ret = gst_v4l2_transform_register (plugin, basename, it->device_path,
+          sink_caps, src_caps);
     /* else if ( ... etc. */
 
     gst_caps_unref (sink_caps);
diff --git a/sys/v4l2/gstv4l2object.c b/sys/v4l2/gstv4l2object.c
index ee759030c..36a2968a2 100644
--- a/sys/v4l2/gstv4l2object.c
+++ b/sys/v4l2/gstv4l2object.c
@@ -1539,6 +1539,10 @@ gst_v4l2_object_add_aspect_ratio (GstV4l2Object * v4l2object, GstStructure * s)
   num = cropcap.pixelaspect.numerator;
   den = cropcap.pixelaspect.denominator;
 
+  /* Ignore PAR that are 0/0 */
+  if (den == 0)
+    return;
+
 done:
   gst_structure_set (s, "pixel-aspect-ratio", GST_TYPE_FRACTION, num, den,
       NULL);
diff --git a/sys/v4l2/gstv4l2transform.c b/sys/v4l2/gstv4l2transform.c
new file mode 100644
index 000000000..cf0c84e7a
--- /dev/null
+++ b/sys/v4l2/gstv4l2transform.c
@@ -0,0 +1,677 @@
+/*
+ * 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_id, 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_start (GstBaseTransform * trans)
+{
+  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
+
+  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 gboolean
+gst_v4l2_transform_stop (GstBaseTransform * trans)
+{
+  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
+
+  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_sinkcaps, NULL);
+
+  return TRUE;
+}
+
+static gboolean
+gst_v4l2_transform_set_caps (GstBaseTransform * trans, GstCaps * incaps,
+    GstCaps * outcaps)
+{
+  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
+
+  /* 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);
+
+  if (!gst_v4l2_object_set_format (self->v4l2output, incaps))
+    goto incaps_failed;
+
+  if (!gst_v4l2_object_set_format (self->v4l2capture, outcaps))
+    goto outcaps_failed;
+
+  return TRUE;
+
+
+incaps_failed:
+  {
+    GST_ERROR_OBJECT (self, "failed to set input caps: %" GST_PTR_FORMAT,
+        incaps);
+    return FALSE;
+  }
+
+outcaps_failed:
+  {
+    gst_v4l2_object_stop (self->v4l2output);
+    GST_ERROR_OBJECT (self, "failed to set output caps: %" GST_PTR_FORMAT,
+        outcaps);
+    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_srccaps);
+      }
+
+      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))
+    ret = GST_BASE_TRANSFORM_CLASS (parent_class)->decide_allocation (trans,
+        query);
+
+  return ret;
+}
+
+/* TODO */
+#if 0
+static gboolean
+gst_v4l2_transform_propose_allocation (GstBaseTransform * trans,
+    GstQuery * decide_query, GstQuery * query)
+{
+  GstV4l2Transform *self = GST_V4L2_TRANSFORM (trans);
+  gboolean ret = FALSE;
+
+  /* FIXME propose alloc this need to be moved from src to v4l2object */
+  if (gst_v4l2_object_propose_allocation (self->v4l2output, query))
+    ret = GST_BASE_TRANSFORM_CLASS (parent_class)->propose_allocation (trans,
+        query);
+
+  return ret;
+}
+#endif
+
+/* 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;
+
+  if (gst_base_transform_is_passthrough (trans)) {
+    GST_DEBUG_OBJECT (self, "Passthrough, no need to do anything");
+    *outbuf = inbuf;
+    goto beach;
+  }
+
+  GST_DEBUG_OBJECT (self, "Queue input buffer");
+  ret = gst_v4l2_buffer_pool_process (GST_V4L2_BUFFER_POOL (pool), inbuf);
+  if (ret != GST_FLOW_OK)
+    goto beach;
+
+  pool = gst_base_transform_get_buffer_pool (trans);
+
+  if (!gst_buffer_pool_is_active (pool)) {
+    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;
+  }
+
+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);
+
+  if (transition == GST_STATE_CHANGE_PAUSED_TO_READY) {
+    gst_v4l2_object_unlock (self->v4l2output);
+    gst_v4l2_object_unlock (self->v4l2capture);
+  }
+
+  return GST_ELEMENT_CLASS (parent_class)->change_state (element, transition);
+}
+
+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_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->start = GST_DEBUG_FUNCPTR (gst_v4l2_transform_start);
+  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);
+  /* TODO */
+#if 0
+  base_transform_class->propose_allocation =
+      GST_DEBUG_FUNCPTR (gst_v4l2_transform_propose_allocation);
+#endif
+  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_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);
+}
+
+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);
+}
+
+/* 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;
+}
diff --git a/sys/v4l2/gstv4l2transform.h b/sys/v4l2/gstv4l2transform.h
new file mode 100644
index 000000000..6c26a9c1d
--- /dev/null
+++ b/sys/v4l2/gstv4l2transform.h
@@ -0,0 +1,80 @@
+/*
+ * 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.
+ *
+ */
+
+#ifndef __GST_V4L2_TRANSFORM_H__
+#define __GST_V4L2_TRANSFORM_H__
+
+#include <gst/gst.h>
+#include <gst/base/gstbasetransform.h>
+
+#include <gstv4l2object.h>
+#include <gstv4l2bufferpool.h>
+
+GST_DEBUG_CATEGORY_EXTERN (v4l2transform_debug);
+
+G_BEGIN_DECLS
+
+#define GST_TYPE_V4L2_TRANSFORM \
+  (gst_v4l2_transform_get_type())
+#define GST_V4L2_TRANSFORM(obj) \
+  (G_TYPE_CHECK_INSTANCE_CAST((obj),GST_TYPE_V4L2_TRANSFORM,GstV4l2Transform))
+#define GST_V4L2_TRANSFORM_CLASS(klass) \
+  (G_TYPE_CHECK_CLASS_CAST((klass),GST_TYPE_V4L2_TRANSFORM,GstV4l2TransformClass))
+#define GST_IS_V4L2_TRANSFORM(obj) \
+  (G_TYPE_CHECK_INSTANCE_TYPE((obj),GST_TYPE_V4L2_TRANSFORM))
+#define GST_IS_V4L2_TRANSFORM_CLASS(obj) \
+  (G_TYPE_CHECK_CLASS_TYPE((klass),GST_TYPE_V4L2_TRANSFORM))
+#define GST_V4L2_TRANSFORM_GET_CLASS(inst) \
+  (G_TYPE_INSTANCE_GET_CLASS ((inst),GST_TYPE_V4L2_TRANSFORM,GstV4l2TransformClass))
+
+typedef struct _GstV4l2Transform GstV4l2Transform;
+typedef struct _GstV4l2TransformClass GstV4l2TransformClass;
+
+struct _GstV4l2Transform
+{
+  GstBaseTransform parent;
+
+  /* < private > */
+  GstV4l2Object * v4l2output;
+  GstV4l2Object * v4l2capture;
+
+  /* pads */
+  GstCaps *probed_srccaps;
+  GstCaps *probed_sinkcaps;
+};
+
+struct _GstV4l2TransformClass
+{
+  GstBaseTransformClass parent_class;
+  gchar *default_device;
+};
+
+GType gst_v4l2_transform_get_type (void);
+
+gboolean gst_v4l2_is_transform       (GstCaps * sink_caps, GstCaps * src_caps);
+gboolean gst_v4l2_transform_register (GstPlugin * plugin,
+                                      const gchar *basename,
+                                      const gchar *device_path,
+                                      GstCaps * sink_caps, GstCaps * src_caps);
+
+G_END_DECLS
+
+#endif /* __GST_V4L2_TRANSFORM_H__ */