avfilter/af_rubberband: flush only if there is something available

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/af_rubberband.c

@@ -175,6 +175,7 @@ static int request_frame(AVFilterLink *outlink)
     ret = ff_request_frame(ctx->inputs[0]);
 
     if (ret == AVERROR_EOF && !s->flushed) {
+        if (rubberband_available(s->rbs) > 0) {
             AVFrame *out = ff_get_audio_buffer(inlink, 1);
             int nb_samples;
 
@@ -183,7 +184,6 @@ static int request_frame(AVFilterLink *outlink)
 
             rubberband_process(s->rbs, (const float *const *)out->data, 1, 1);
             av_frame_free(&out);
-        s->flushed = 1;
             nb_samples = rubberband_available(s->rbs);
 
             if (nb_samples > 0) {
@@ -198,6 +198,8 @@ static int request_frame(AVFilterLink *outlink)
                 ret = ff_filter_frame(outlink, out);
                 s->nb_samples_out += nb_samples;
             }
+        }
+        s->flushed = 1;
         av_log(ctx, AV_LOG_DEBUG, "nb_samples_in %"PRId64" nb_samples_out %"PRId64"\n",
                                    s->nb_samples_in, s->nb_samples_out);
     }