v4l2object: use G_SELECTION instead of G_CROP in gst_v4l2_object_acquire_format

The gst_v4l2_object_acquire_format() function is used by v4l2videodec to obtain
the currently set capture format. Since G_FMT returns the coded size, the
visible size needs to be obtained from the compose rectangle in order to
negotiate it with downstream elements. The G_CROP call hasn't worked on mem2mem
capture queues for a long time. Instead use the G_SELECTION call to obtain the
compose rectangle and only fall back to G_CROP for ancient kernels.

https://bugzilla.gnome.org/show_bug.cgi?id=766381

diff --git a/sys/v4l2/gstv4l2object.c b/sys/v4l2/gstv4l2object.c
index cf12823..0d145fb 100644 (file)
--- a/sys/v4l2/gstv4l2object.c
+++ b/sys/v4l2/gstv4l2object.c
@@ -3632,6 +3632,8 @@ gst_v4l2_object_acquire_format (GstV4l2Object * v4l2object, GstVideoInfo * info)
   struct v4l2_fmtdesc *fmtdesc;
   struct v4l2_format fmt;
   struct v4l2_crop crop;
+  struct v4l2_selection sel;
+  struct v4l2_rect *r = NULL;
   GstVideoFormat format;
   guint width, height;
   GstVideoAlignment align;
@@ -3662,15 +3664,26 @@ gst_v4l2_object_acquire_format (GstV4l2Object * v4l2object, GstVideoInfo * info)
   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;
+  /* Use the default compose rectangle */
+  memset (&sel, 0, sizeof (struct v4l2_selection));
+  sel.type = v4l2object->type;
+  sel.target = V4L2_SEL_TGT_COMPOSE_DEFAULT;
+  if (v4l2_ioctl (v4l2object->video_fd, VIDIOC_G_SELECTION, &sel) >= 0) {
+    r = &sel.r;
+  } else {
+    /* For ancient kernels, fall back to G_CROP */
+    memset (&crop, 0, sizeof (struct v4l2_crop));
+    crop.type = v4l2object->type;
+    if (v4l2_ioctl (v4l2object->video_fd, VIDIOC_G_CROP, &crop) >= 0)
+      r = &crop.c;
+  }
+  if (r) {
+    align.padding_left = r->left;
+    align.padding_top = r->top;
+    align.padding_right = width - r->width - r->left;
+    align.padding_bottom = height - r->height - r->top;
+    width = r->width;
+    height = r->height;
   }
 
   gst_video_info_set_format (info, format, width, height);