libvorbis: only store version string if bitexact is not set.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/libvorbis.c

@@ -226,6 +226,7 @@ static av_cold int oggvorbis_encode_init(AVCodecContext *avctx)
     }
 
     vorbis_comment_init(&s->vc);
+    if (!(avctx->flags & CODEC_FLAG_BITEXACT))
         vorbis_comment_add_tag(&s->vc, "encoder", LIBAVCODEC_IDENT);
 
     if ((ret = vorbis_analysis_headerout(&s->vd, &s->vc, &header, &header_comm,