video: Make gst_buffer_get_video_meta() a real function, Return lowest id

Instead of returning the first video meta found on a buffer, return the
one with the lowest id (which is usually the same thing, except on
multi-view buffers)

gst-libs/gst/video/gstvideometa.c

@@ -96,6 +96,38 @@ gst_video_meta_get_info (void)
   return video_meta_info;
 }
 
+/**
+ * gst_buffer_get_video_meta:
+ * @buffer: a #GstBuffer
+ *
+ * Find the #GstVideoMeta on @buffer with the lowest @id.
+ *
+ * Buffers can contain multiple #GstVideoMeta metadata items when dealing with
+ * multiview buffers.
+ *
+ * Returns: the #GstVideoMeta with lowest id (usually 0) or %NULL when there
+ * is no such metadata on @buffer.
+ */
+GstVideoMeta *
+gst_buffer_get_video_meta (GstBuffer * buffer)
+{
+  gpointer state = NULL;
+  GstVideoMeta *out = NULL;
+  GstMeta *meta;
+  const GstMetaInfo *info = GST_VIDEO_META_INFO;
+
+  while ((meta = gst_buffer_iterate_meta (buffer, &state))) {
+    if (meta->info->api == info->api) {
+      GstVideoMeta *vmeta = (GstVideoMeta *) meta;
+      if (vmeta->id == 0)
+        return vmeta;           /* Early out for id 0 */
+      if (out == NULL || vmeta->id < out->id)
+        out = vmeta;
+    }
+  }
+  return out;
+}
+
 /**
  * gst_buffer_get_video_meta_id:
  * @buffer: a #GstBuffer

gst-libs/gst/video/gstvideometa.h

@@ -78,7 +78,7 @@ struct _GstVideoMeta {
 GType gst_video_meta_api_get_type (void);
 const GstMetaInfo * gst_video_meta_get_info (void);
 
-#define gst_buffer_get_video_meta(b) ((GstVideoMeta*)gst_buffer_get_meta((b),GST_VIDEO_META_API_TYPE))
+GstVideoMeta * gst_buffer_get_video_meta (GstBuffer *buffer);
 GstVideoMeta * gst_buffer_get_video_meta_id    (GstBuffer *buffer, gint id);
 
 GstVideoMeta * gst_buffer_add_video_meta       (GstBuffer *buffer, GstVideoFrameFlags flags,

win32/common/libgstvideo.def

@@ -6,6 +6,7 @@ EXPORTS
 	gst_buffer_add_video_overlay_composition_meta
 	gst_buffer_add_video_region_of_interest_meta
 	gst_buffer_add_video_region_of_interest_meta_id
+	gst_buffer_get_video_meta
 	gst_buffer_get_video_meta_id
 	gst_buffer_get_video_region_of_interest_meta_id
 	gst_buffer_pool_config_get_video_alignment