1 files changed, 5 insertions, 1 deletions
diff --git a/libavcodec/mpegvideo.h b/libavcodec/mpegvideo.h
index fd89f38e57..80e0f9065f 100644
--- a/libavcodec/mpegvideo.h
+++ b/libavcodec/mpegvideo.h
@@ -162,7 +162,11 @@ typedef struct MotionEstContext{
     uint32_t *score_map;               ///< map to store the scores
     int map_generation;
     int pre_penalty_factor;
-    int penalty_factor;
+    int penalty_factor;                /*!< an estimate of the bits required to
+                                        code a given mv value, e.g. (1,0) takes
+                                        more bits than (0,0). We have to
+                                        estimate whether any reduction in
+                                        residual is worth the extra bits. */
     int sub_penalty_factor;
     int mb_penalty_factor;
     int flags;