[FFmpeg-devel] [PATCH 3/3] aaccoder: Improve IS phase rejection

[Rostislav Pehlivanov]

This commit adds a slightly more robust way of determining whether the phases
match or are too different for IS to be used.
---
 libavcodec/aaccoder.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/libavcodec/aaccoder.c b/libavcodec/aaccoder.c
index 17b14d6..bd232f6 100644
--- a/libavcodec/aaccoder.c
+++ b/libavcodec/aaccoder.c
@@ -56,6 +56,9 @@
 /** Frequency in Hz for lower limit of intensity stereo   **/
 #define INT_STEREO_LOW_LIMIT 6100
 
+/** If less than this fraction of coeff phases agree disable IS for that band **/
+#define IS_PHASE_DIFF_LIM 0.11
+
 /** Total number of usable codebooks **/
 #define CB_TOT 12
 
@@ -1218,9 +1221,9 @@ static void search_for_is(AACEncContext *s, AVCodecContext *avctx, ChannelElemen
                         ener01 += (coef0 + coef1)*(coef0 + coef1);
                     }
                 }
-                if (!phase) { /* Too much phase difference between channels */
+                if (fabs(phase)/(sce0->ics.group_len[w]*sce0->ics.swb_sizes[g]) < IS_PHASE_DIFF_LIM) {
                     start += sce0->ics.swb_sizes[g];
-                    continue;
+                    continue; /* Too much phase difference */
                 }
                 phase = av_clip(phase, -1, 1);
                 for (w2 = 0; w2 < sce0->ics.group_len[w]; w2++) {
-- 
2.4.3.573.g4eafbef