v4l2: set min_latency for output device according to required minimum number of buffers

Since we can get the minimum number of buffers needed by an output
device to work, use it to set min_latency which will determine how many
buffers are queued.

https://bugzilla.gnome.org/show_bug.cgi?id=736072

diff --git a/sys/v4l2/gstv4l2bufferpool.c b/sys/v4l2/gstv4l2bufferpool.c
index 8851571..d00d123 100644 (file)
--- a/sys/v4l2/gstv4l2bufferpool.c
+++ b/sys/v4l2/gstv4l2bufferpool.c
@@ -623,8 +623,10 @@ gst_v4l2_buffer_pool_start (GstBufferPool * bpool)
           &max_buffers))
     goto wrong_config;
 
-  /* TODO Also consider min_buffers_for_output when implemented */
-  min_latency = MAX (GST_V4L2_MIN_BUFFERS, obj->min_buffers_for_capture);
+  if (V4L2_TYPE_IS_OUTPUT (obj->type))
+    min_latency = MAX (GST_V4L2_MIN_BUFFERS, obj->min_buffers_for_output);
+  else
+    min_latency = MAX (GST_V4L2_MIN_BUFFERS, obj->min_buffers_for_capture);
 
   switch (obj->mode) {
     case GST_V4L2_IO_RW:

diff --git a/sys/v4l2/gstv4l2object.c b/sys/v4l2/gstv4l2object.c
index 8021490..9073a48 100644 (file)
--- a/sys/v4l2/gstv4l2object.c
+++ b/sys/v4l2/gstv4l2object.c
@@ -3472,10 +3472,13 @@ gst_v4l2_object_propose_allocation (GstV4l2Object * obj, GstQuery * query)
   if (v4l2_ioctl (obj->video_fd, VIDIOC_G_CTRL, &ctl) >= 0) {
     GST_DEBUG_OBJECT (obj->element, "driver require a miminum of %d buffers",
         ctl.value);
-
-    min = MAX (ctl.value, GST_V4L2_MIN_BUFFERS);
+    obj->min_buffers_for_output = ctl.value;
+  } else {
+    obj->min_buffers_for_output = 0;
   }
 
+  min = MAX (obj->min_buffers_for_output, GST_V4L2_MIN_BUFFERS);
+
   gst_query_add_allocation_pool (query, pool, size, min, max);
 
   /* we also support various metadata */

diff --git a/sys/v4l2/gstv4l2object.h b/sys/v4l2/gstv4l2object.h
index c13cd64..141f62d 100644 (file)
--- a/sys/v4l2/gstv4l2object.h
+++ b/sys/v4l2/gstv4l2object.h
@@ -121,6 +121,9 @@ struct _GstV4l2Object {
    * calculate the minimum latency of a m2m decoder. */
   guint32 min_buffers_for_capture;
 
+  /* This will be set if supported in propose allocation. */
+  guint32 min_buffers_for_output;
+
   /* wanted mode */
   GstV4l2IOMode req_mode;