aacenc: TLS: Try to preserve some energy in each non-zero band.

Reduce scalefactors in non-zero bands that underflow by twice as much as those
in bands that just fail to hit psy targets.

Originally committed as revision 24482 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/aaccoder.c

@@ -806,13 +806,18 @@ static void search_for_quantizers_twoloop(AVCodecContext *avctx,
             for (g = 0; g < sce->ics.num_swb; g++) {
                 int prevsc = sce->sf_idx[w*16+g];
                 const float *scaled = s->scoefs + start;
-                if (dists[w*16+g] > uplims[w*16+g] && sce->sf_idx[w*16+g] > 60)
+                if (dists[w*16+g] > uplims[w*16+g] && sce->sf_idx[w*16+g] > 60) {
+                    if (find_min_book(find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], scaled), sce->sf_idx[w*16+g]-1))
                     sce->sf_idx[w*16+g]--;
+                    else //Try to make sure there is some energy in every band
+                        sce->sf_idx[w*16+g]-=2;
+                }
                 sce->sf_idx[w*16+g] = av_clip(sce->sf_idx[w*16+g], minscaler, minscaler + SCALE_MAX_DIFF);
                 sce->sf_idx[w*16+g] = FFMIN(sce->sf_idx[w*16+g], 219);
                 if (sce->sf_idx[w*16+g] != prevsc)
                     fflag = 1;
                 sce->band_type[w*16+g] = find_min_book(find_max_val(sce->ics.group_len[w], sce->ics.swb_sizes[g], scaled), sce->sf_idx[w*16+g]);
+//av_log(NULL, AV_LOG_ERROR, "w %d swb %2d sf %3d bt %2d dist %f uplim %f ratio %f\n", w, g, sce->sf_idx[w*16+g], sce->band_type[w*16+g], dists[w*16+g], uplims[w*16+g], dists[w*16+g]/uplims[w*16+g]);
                 start += sce->ics.swb_sizes[g];
             }
         }