diff --git a/libavcodec/avcodec.h b/libavcodec/avcodec.h
index cb0e744622..3d6f7b9333 100644
--- a/libavcodec/avcodec.h
+++ b/libavcodec/avcodec.h
@@ -1346,6 +1346,8 @@ typedef struct AVCodecContext {
      * of which frame timestamps are represented. For fixed-fps content,
      * timebase should be 1/framerate and timestamp increments should be
      * identically 1.
+     * This often, but not always is the inverse of the frame rate or field rate
+     * for video.
      * - encoding: MUST be set by user.
      * - decoding: the use of this field for decoding is deprecated.
      *             Use framerate instead.