[FFmpeg-devel] [PATCH v2 3/8] aaccoder: fix M/S coding

[Rostislav Pehlivanov]

There were some mistakes in the code for M/S stereo, this commit fixes them. The start variable was not being reset for every window and every access to the coefficients was incorrect as well. This fixes that by properly addressing the coefficients using both windows and setting the start on every window to zero.
---
 libavcodec/aaccoder.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 3fcc8b4..33cbe7b 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -1143,6 +1143,7 @@ static void search_for_ms(AACEncContext *s, ChannelElement *cpe,
     if (!cpe->common_window)
         return;
     for (w = 0; w < sce0->ics.num_windows; w += sce0->ics.group_len[w]) {
+        start = 0;
         for (g = 0;  g < sce0->ics.num_swb; g++) {
             if (!cpe->ch[0].zeroes[w*16+g] && !cpe->ch[1].zeroes[w*16+g]) {
                 float dist1 = 0.0f, dist2 = 0.0f;
@@ -1152,22 +1153,22 @@ static void search_for_ms(AACEncContext *s, ChannelElement *cpe,
                     float minthr = FFMIN(band0->threshold, band1->threshold);
                     float maxthr = FFMAX(band0->threshold, band1->threshold);
                     for (i = 0; i < sce0->ics.swb_sizes[g]; i++) {
-                        M[i] = (sce0->pcoeffs[start+w2*128+i]
-                              + sce1->pcoeffs[start+w2*128+i]) * 0.5;
+                        M[i] = (sce0->pcoeffs[start+(w+w2)*128+i]
+                              + sce1->pcoeffs[start+(w+w2)*128+i]) * 0.5;
                         S[i] =  M[i]
-                              - sce1->pcoeffs[start+w2*128+i];
+                              - sce1->pcoeffs[start+(w+w2)*128+i];
                     }
-                    abs_pow34_v(L34, sce0->coeffs+start+w2*128, sce0->ics.swb_sizes[g]);
-                    abs_pow34_v(R34, sce1->coeffs+start+w2*128, sce0->ics.swb_sizes[g]);
+                    abs_pow34_v(L34, sce0->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
+                    abs_pow34_v(R34, sce1->coeffs+start+(w+w2)*128, sce0->ics.swb_sizes[g]);
                     abs_pow34_v(M34, M,                         sce0->ics.swb_sizes[g]);
                     abs_pow34_v(S34, S,                         sce0->ics.swb_sizes[g]);
-                    dist1 += quantize_band_cost(s, sce0->coeffs + start + w2*128,
+                    dist1 += quantize_band_cost(s, sce0->coeffs + start + (w+w2)*128,
                                                 L34,
                                                 sce0->ics.swb_sizes[g],
                                                 sce0->sf_idx[(w+w2)*16+g],
                                                 sce0->band_type[(w+w2)*16+g],
                                                 lambda / band0->threshold, INFINITY, NULL);
-                    dist1 += quantize_band_cost(s, sce1->coeffs + start + w2*128,
+                    dist1 += quantize_band_cost(s, sce1->coeffs + start + (w+w2)*128,
                                                 R34,
                                                 sce1->ics.swb_sizes[g],
                                                 sce1->sf_idx[(w+w2)*16+g],
-- 
2.1.4