lavd: add categories to device implementations

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>

libavdevice/v4l2enc.c

@@ -97,6 +97,13 @@ static int write_trailer(AVFormatContext *s1)
     return 0;
 }
 
+static const AVClass v4l2_class = {
+    .class_name = "V4L2 outdev",
+    .item_name  = av_default_item_name,
+    .version    = LIBAVUTIL_VERSION_INT,
+    .category   = AV_CLASS_CATEGORY_DEVICE_VIDEO_OUTPUT,
+};
+
 AVOutputFormat ff_v4l2_muxer = {
     .name           = "v4l2",
     .long_name      = NULL_IF_CONFIG_SMALL("Video4Linux2 output device"),
@@ -107,4 +114,5 @@ AVOutputFormat ff_v4l2_muxer = {
     .write_packet   = write_packet,
     .write_trailer  = write_trailer,
     .flags          = AVFMT_NOFILE,
+    .priv_class     = &v4l2_class,
 };