avcodec/mpegvideo_enc: Avoid fine lambda steps in VBV retry code when RD is not in use

Reduces the number of times the vbv retry code is used and should have no
effect on quality
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/mpegvideo_enc.c

@@ -1824,16 +1824,18 @@ vbv_retry:
         if (avctx->rc_buffer_size) {
             RateControlContext *rcc = &s->rc_context;
             int max_size = FFMAX(rcc->buffer_index * avctx->rc_max_available_vbv_use, rcc->buffer_index - 500);
+            int hq = (s->avctx->mb_decision == FF_MB_DECISION_RD || s->avctx->trellis);
+            int min_step = hq ? 1 : (1<<(FF_LAMBDA_SHIFT + 7))/139;
 
             if (put_bits_count(&s->pb) > max_size &&
                 s->lambda < s->lmax) {
-                s->next_lambda = FFMAX(s->lambda + 1, s->lambda *
+                s->next_lambda = FFMAX(s->lambda + min_step, s->lambda *
                                        (s->qscale + 1) / s->qscale);
                 if (s->adaptive_quant) {
                     int i;
                     for (i = 0; i < s->mb_height * s->mb_stride; i++)
                         s->lambda_table[i] =
-                            FFMAX(s->lambda_table[i] + 1,
+                            FFMAX(s->lambda_table[i] + min_step,
                                   s->lambda_table[i] * (s->qscale + 1) /
                                   s->qscale);
                 }