libvorbis: Disable strict bitrate management when not requested

This is 3 times faster in a quick benchmark

Originally committed as revision 23471 to svn://svn.ffmpeg.org/ffmpeg/trunk

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 */
-        if(vorbis_encode_ctl(vi, OV_ECTL_RATEMANAGE2_SET, NULL))
-            return -1;
-#endif
+        /* 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;
     }
 
     /* cutoff frequency */