AAC encoder: Fix application of M/S with PNS

When both M/S coding and PNS are enabled, scalefactors
and coding books would be mistakenly clobbered when setting
the M/S flag on PNS'd bands. The flag needs to be set to
signal the generation of correlated noise, but the scalefactors,
coefficients and the coding books need to be kept intact.

libavcodec/aaccoder.c

@@ -887,8 +887,8 @@ static void search_for_ms(AACEncContext *s, ChannelElement *cpe)
                     }
                     cpe->ms_mask[w*16+g] = dist2 <= dist1 && B1 < B0;
                     if (cpe->ms_mask[w*16+g]) {
-                        /* Setting the M/S mask is useful with I/S, but only the flag */
-                        if (!cpe->is_mask[w*16+g]) {
+                        /* Setting the M/S mask is useful with I/S or PNS, but only the flag */
+                        if (!cpe->is_mask[w*16+g] && sce0->band_type[w*16+g] != NOISE_BT && sce1->band_type[w*16+g] != NOISE_BT) {
                             sce0->sf_idx[w*16+g] = mididx;
                             sce1->sf_idx[w*16+g] = sididx;
                             sce0->band_type[w*16+g] = midcb;

libavcodec/aacenc.c

@@ -292,7 +292,13 @@ static void apply_mid_side_stereo(ChannelElement *cpe)
         for (w2 =  0; w2 < ics->group_len[w]; w2++) {
             int start = (w+w2) * 128;
             for (g = 0; g < ics->num_swb; g++) {
-                if (!cpe->ms_mask[w*16 + g] && !cpe->is_mask[w*16 + g]) {
+                /* ms_mask can be used for other purposes in PNS and I/S,
+                 * so must not apply M/S if any band uses either, even if
+                 * ms_mask is set.
+                 */
+                if (!cpe->ms_mask[w*16 + g] || cpe->is_mask[w*16 + g]
+                    || cpe->ch[0].band_type[w*16 + g] == NOISE_BT
+                    || cpe->ch[1].band_type[w*16 + g] == NOISE_BT) {
                     start += ics->swb_sizes[g];
                     continue;
                 }