libvpxenc: use the default bitrate if not set

Signed-off-by: Luca Barbato <lu_zero@gentoo.org>

libavcodec/libvpxenc.c

@@ -245,11 +245,16 @@ static av_cold int vp8_init(AVCodecContext *avctx)
     else
         enccfg.g_pass = VPX_RC_ONE_PASS;
 
+    if (!avctx->bit_rate)
+        avctx->bit_rate = enccfg.rc_target_bitrate * 1000;
+    else
+        enccfg.rc_target_bitrate = av_rescale_rnd(avctx->bit_rate, 1, 1000,
+                                              AV_ROUND_NEAR_INF);
+
     if (avctx->rc_min_rate == avctx->rc_max_rate &&
         avctx->rc_min_rate == avctx->bit_rate)
         enccfg.rc_end_usage = VPX_CBR;
-    enccfg.rc_target_bitrate = av_rescale_rnd(avctx->bit_rate, 1, 1000,
-                                              AV_ROUND_NEAR_INF);
+
     if (avctx->qmin > 0)
         enccfg.rc_min_quantizer = avctx->qmin;
     if (avctx->qmax > 0)