v4l2src: Add source-change / resolution-change support

This branch adds support for driver driven source changes along with DV_TIMING locking support. Effectively, drivers can emit SOURCE_CHANGE event, with the RESOLUTION_CHANGE flag in order to signal that something got changes at the input signal. In that situation, we need to reset (streamoff/on) as we may not get more data otherwise. While doing this, we now query for detected DV_TIMING (aka modes) and lock/set these. We also default to the link detected width/height/framerate.

As a bonus, v4l2src will now mimic decklinksrc when the signal is lost and recovered. A WARNING with RESSOURCE/READ will be emited when the signal is lost, and an INFO message again with RESSOURCE/READ for when it's recovered.

This has been tested with vivid test driver and an work in progress HDMI receiver driver.

sys/v4l2/gstv4l2bufferpool.c

@@ -1112,7+1112,7 @@
     }
   }
 
   if (gst_poll_fd_has_error (pool->poll, &pool->pollfd))
     goto select_error;
 
   /* PRI is used to signal that events are available */
@@ -2201,7+2201,7 @@
 void
 gst_v4l2_buffer_pool_enable_resolution_change (GstV4l2BufferPool * pool)
 {
+  guint32 input_id = 0;
+
   g_return_if_fail (!gst_buffer_pool_is_active (GST_BUFFER_POOL (pool)));
 
-  if (gst_v4l2_subscribe_event (pool->obj, V4L2_EVENT_SOURCE_CHANGE))
+  /* Make sure we subscribe for the current input */
+  gst_v4l2_get_input (pool->obj, &input_id);
+
+  if (gst_v4l2_subscribe_event (pool->obj, V4L2_EVENT_SOURCE_CHANGE, input_id))
     gst_poll_fd_ctl_pri (pool->poll, &pool->pollfd, TRUE);
 }