avfilter/af_rubberband: adjust nb_samples after every command

libavfilter/af_rubberband.c

@@ -212,6 +212,7 @@ static int process_command(AVFilterContext *ctx, const char *cmd, const char *ar
 
     rubberband_set_time_ratio(s->rbs, 1. / s->tempo);
     rubberband_set_pitch_scale(s->rbs, s->pitch);
+    s->nb_samples = rubberband_get_samples_required(s->rbs);
 
     return 0;
 }