Document how VP9 treats a negative speed value

Change-Id: I12948b08a7bb5beb5024b8676de9dafc239f8e89

diff --git a/vpx/vp8cx.h b/vpx/vp8cx.h
index 3c0278c..d098c4c 100644 (file)
--- a/vpx/vp8cx.h
+++ b/vpx/vp8cx.h
@@ -166,6 +166,7 @@ enum vp8e_enc_control_id {
    *
    * \note Valid range for VP8: -16..16
    * \note Valid range for VP9: -9..9
+   * \note A negative value (-n) is treated as its absolute value (n) in VP9.
    *
    * Supported in codecs: VP8, VP9
    */