diff --git a/spa/include/spa/param/format.h b/spa/include/spa/param/format.h
index b898c7099..fa316076c 100644
--- a/spa/include/spa/param/format.h
+++ b/spa/include/spa/param/format.h
@@ -120,7 +120,8 @@ enum spa_format {
 	/* Video Format keys */
 	SPA_FORMAT_START_Video = 0x20000,
 	SPA_FORMAT_VIDEO_format,		/**< video format (Id enum spa_video_format) */
-	SPA_FORMAT_VIDEO_modifier,		/**< format modifier (Long) */
+	SPA_FORMAT_VIDEO_modifier,		/**< format modifier (Long)
+						  * use only with DMA-BUF and omit for other buffer types */
 	SPA_FORMAT_VIDEO_size,			/**< size (Rectangle) */
 	SPA_FORMAT_VIDEO_framerate,		/**< frame rate (Fraction) */
 	SPA_FORMAT_VIDEO_maxFramerate,		/**< maximum frame rate (Fraction) */
diff --git a/spa/include/spa/param/video/raw.h b/spa/include/spa/param/video/raw.h
index 17d5ba073..e1d1b73ad 100644
--- a/spa/include/spa/param/video/raw.h
+++ b/spa/include/spa/param/video/raw.h
@@ -177,7 +177,8 @@ enum spa_video_interlace_mode {
  */
 struct spa_video_info_raw {
 	enum spa_video_format format;				/**< the format */
-	int64_t modifier;					/**< format modifier */
+	int64_t modifier;					/**< format modifier
+								  * only used with DMA-BUF */
 	struct spa_rectangle size;				/**< the frame size of the video */
 	struct spa_fraction framerate;				/**< the framerate of the video, 0/1 means variable rate */
 	struct spa_fraction max_framerate;			/**< the maximum framerate of the video. This is only valid when