use AVFormatContext to log

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@6731 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/gxfenc.c

@@ -645,7 +645,7 @@ static int gxf_write_header(AVFormatContext *s)
                 }
                 break;
             default:
-                av_log(NULL, AV_LOG_ERROR, "video codec not supported\n");
+                av_log(s, AV_LOG_ERROR, "video codec not supported\n");
                 return -1;
             }
         }