Have xvid encoder wrapper honnor -vtag option

Patch by Ramiro Polla angustia A arrozcru P no-ip P org
Original thread:
Date: 14.10.2006 05:44
Subject: [Ffmpeg-devel] xvid ignores -vtag

Originally committed as revision 6701 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/xvidff.c

@@ -335,6 +335,7 @@ int ff_xvid_encode_init(AVCodecContext *avctx)  {
     } else {
         /* We are claiming to be XviD */
         x->quicktime_format = 0;
+        if(!avctx->codec_tag)
             avctx->codec_tag = ff_get_fourcc("xvid");
     }