avformat/img2enc: mention -frames:v in error message

Signed-off-by: Lou Logan <lou@lrcd.com>
Signed-off-by: Kieran O Leary <kieran.o.leary@gmail.com>

libavformat/img2enc.c

@@ -110,7 +110,8 @@ static int write_packet(AVFormatContext *s, AVPacket *pkt)
                                           AV_FRAME_FILENAME_FLAGS_MULTIPLE) < 0 &&
                    img->img_number > 1) {
             av_log(s, AV_LOG_ERROR,
-                   "Could not get frame filename number %d from pattern '%s' (either set update or use a pattern like %%03d within the filename pattern)\n",
+                   "Could not get frame filename number %d from pattern '%s'. "
+                   "Use '-frames:v 1' for a single image, or '-update' option, or use a pattern such as %%03d within the filename.\n",
                    img->img_number, img->path);
             return AVERROR(EINVAL);
         }