diff --git a/libavformat/yuv4mpegenc.c b/libavformat/yuv4mpegenc.c
index 6120c7e520808c012b86e06c8c231a89d89d8f5c..23d2eda45c7223b3efe034f8e9c76c74dae25081 100644
--- a/libavformat/yuv4mpegenc.c
+++ b/libavformat/yuv4mpegenc.c
@@ -209,6 +209,7 @@ static int yuv4_write_packet(AVFormatContext *s, AVPacket *pkt)
         // Adjust for smaller Cb and Cr planes
         av_pix_fmt_get_chroma_sub_sample(st->codec->pix_fmt, &h_chroma_shift,
                                          &v_chroma_shift);
+        // Shift right, rounding up
         width  = AV_CEIL_RSHIFT(width,  h_chroma_shift);
         height = AV_CEIL_RSHIFT(height, v_chroma_shift);