v4l2object: Add V4L2_CID_MIN_BUFFERS_FOR_CAPTURE support

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

diff --git a/sys/v4l2/gstv4l2object.c b/sys/v4l2/gstv4l2object.c
index ed363a6..a93b4ad 100644 (file)
--- a/sys/v4l2/gstv4l2object.c
+++ b/sys/v4l2/gstv4l2object.c
@@ -3146,6 +3146,7 @@ gst_v4l2_object_decide_allocation (GstV4l2Object * obj, GstQuery * query)
   GstBufferPool *pool;
   guint size, min, max;
   gboolean update;
+  struct v4l2_control ctl = { 0, };
 
   GST_DEBUG_OBJECT (obj->element, "decide allocation");
 
@@ -3173,6 +3174,14 @@ gst_v4l2_object_decide_allocation (GstV4l2Object * obj, GstQuery * query)
     min = 2;
   }
 
+  /* Certain driver may expose a minimum through controls */
+  ctl.id = V4L2_CID_MIN_BUFFERS_FOR_CAPTURE;
+  if (v4l2_ioctl (obj->video_fd, VIDIOC_G_CTRL, &ctl) >= 0) {
+    GST_DEBUG_OBJECT (obj->element, "driver require a minimum of %d buffers",
+        ctl.value);
+    min += ctl.value;
+  }
+
   /* select a pool */
   switch (obj->mode) {
     case GST_V4L2_IO_RW: