libvorbis: Disable strict bitrate management when not requested

This is 3 times faster in a quick benchmark

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@23471 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavcodec/libvorbis.c

@@ -68,11 +68,10 @@ static av_cold int oggvorbis_init_encoder(vorbis_info *vi, AVCodecContext *avcco
                 avccontext->sample_rate, minrate, avccontext->bit_rate, maxrate))
             return -1;
 
-#ifdef OGGVORBIS_VBR_BY_ESTIMATE
-        /* variable bitrate by estimate */
+        /* variable bitrate by estimate, disable slow rate management */
+        if(minrate == -1 && maxrate == -1)
             if(vorbis_encode_ctl(vi, OV_ECTL_RATEMANAGE2_SET, NULL))
                 return -1;
-#endif
     }
 
     /* cutoff frequency */