v4l2object: Implement _setup_format()

This method allow setting up the object from the currently configured format on the
device. This is useful for M2M element where input data decides the format that will
be set on capture side.

https://bugzilla.gnome.org/show_bug.cgi?id=720568

sys/v4l2/gstv4l2object.c

@@ -2889,6 +2889,102 @@ pool_failed:
   }
 }
 
+/**
+ * gst_v4l2_object_setup_format:
+ * @v4l2object the object
+ * @info a GstVideoInfo to be filled
+ * @align a GstVideoAlignment to be filled
+ *
+ * Setup the format base on the currently configured format. This is useful in
+ * decoder or encoder elements where the output format is dictated by the
+ * input.
+ *
+ * Returns: %TRUE on success, %FALSE on failure.
+ */
+gboolean
+gst_v4l2_object_setup_format (GstV4l2Object * v4l2object,
+    GstVideoInfo * info, GstVideoAlignment * align)
+{
+  struct v4l2_fmtdesc *fmtdesc;
+  struct v4l2_format fmt;
+  struct v4l2_crop crop;
+  GstVideoFormat format;
+  guint width, height;
+
+  gst_video_info_init (info);
+  gst_video_alignment_reset (align);
+
+  memset (&fmt, 0x00, sizeof (struct v4l2_format));
+  fmt.type = v4l2object->type;
+  if (v4l2_ioctl (v4l2object->video_fd, VIDIOC_G_FMT, &fmt) < 0)
+    goto get_fmt_failed;
+
+  fmtdesc = gst_v4l2_object_get_format_from_fourcc (v4l2object,
+      fmt.fmt.pix.pixelformat);
+  if (fmtdesc == NULL)
+    goto unsupported_format;
+
+  /* No need to care about mplane, the four first params are the same */
+  format = gst_v4l2_object_v4l2fourcc_to_video_format (fmt.fmt.pix.pixelformat);
+  width = fmt.fmt.pix.width;
+  height = fmt.fmt.pix.height;
+
+  memset (&crop, 0, sizeof (struct v4l2_crop));
+  crop.type = v4l2object->type;
+  if (v4l2_ioctl (v4l2object->video_fd, VIDIOC_G_CROP, &crop) >= 0) {
+    align->padding_left = crop.c.left;
+    align->padding_top = crop.c.top;
+    align->padding_right = width - crop.c.width - crop.c.left;
+    align->padding_bottom = height - crop.c.height - crop.c.top;
+    width = crop.c.width;
+    height = crop.c.height;
+  }
+
+  gst_video_info_set_format (info, format, width, height);
+
+  switch (fmt.fmt.pix.field) {
+    case V4L2_FIELD_ANY:
+    case V4L2_FIELD_NONE:
+      info->interlace_mode = GST_VIDEO_INTERLACE_MODE_PROGRESSIVE;
+      break;
+    case V4L2_FIELD_INTERLACED:
+    case V4L2_FIELD_INTERLACED_TB:
+    case V4L2_FIELD_INTERLACED_BT:
+      info->interlace_mode = GST_VIDEO_INTERLACE_MODE_INTERLEAVED;
+      break;
+    default:
+      goto unsupported_field;
+  }
+
+  gst_v4l2_object_save_format (v4l2object, fmtdesc, &fmt, info);
+
+  /* Shall we setup the pool ? */
+
+  return TRUE;
+
+get_fmt_failed:
+  {
+    GST_ELEMENT_WARNING (v4l2object->element, RESOURCE, SETTINGS,
+        (_("Video device did not provide output format.")), GST_ERROR_SYSTEM);
+    return FALSE;
+  }
+unsupported_field:
+  {
+    GST_ELEMENT_ERROR (v4l2object->element, RESOURCE, SETTINGS,
+        (_("Video devices uses an unsupported interlacing method.")),
+        ("V4L2 field type %d not supported", fmt.fmt.pix.field));
+    return FALSE;
+  }
+unsupported_format:
+  {
+    GST_ELEMENT_ERROR (v4l2object->element, RESOURCE, SETTINGS,
+        (_("Video devices uses an unsupported pixel format.")),
+        ("V4L2 format %" GST_FOURCC_FORMAT " not supported",
+            GST_FOURCC_ARGS (fmt.fmt.pix.pixelformat)));
+    return FALSE;
+  }
+}
+
 gboolean
 gst_v4l2_object_caps_equal (GstV4l2Object * v4l2object, GstCaps * caps)
 {

sys/v4l2/gstv4l2object.h

@@ -274,6 +274,10 @@ gboolean      gst_v4l2_object_copy        (GstV4l2Object * v4l2object,
 GstCaps *     gst_v4l2_object_get_caps    (GstV4l2Object * v4l2object,
                                            GstCaps * filter);
 
+gboolean      gst_v4l2_object_setup_format (GstV4l2Object * v4l2object,
+                                            GstVideoInfo * info,
+                                            GstVideoAlignment * align);
+
 
 
 #define GST_IMPLEMENT_V4L2_PROBE_METHODS(Type_Class, interface_as_function)                 \