From 6cb3b0e30321d6d514406fc2eb29f78a729c8642 Mon Sep 17 00:00:00 2001
From: Hendrik Leppkes <h.leppkes@gmail.com>
Date: Sun, 16 Dec 2012 10:03:27 +0100
Subject: [PATCH] swresample: add a "clipping protection" mode when mixing

This mode normalizes audio down to stay below 1.0 after mixing, so no clipping occurs when converting to integer formats.
---
 libswresample/options.c             |  1 +
 libswresample/rematrix.c            | 20 +++++++++++++++++++-
 libswresample/swresample_internal.h |  3 +++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/libswresample/options.c b/libswresample/options.c
index a3284a4896..1684048831 100644
--- a/libswresample/options.c
+++ b/libswresample/options.c
@@ -122,6 +122,7 @@ static const AVOption options[]={
 { "kaiser_beta"         , "set swr Kaiser window beta"  , OFFSET(kaiser_beta)    , AV_OPT_TYPE_DOUBLE  , {.dbl=9                     }, 2      , 16        , PARAM },
 
 { "output_sample_bits"  , "set swr number of output sample bits", OFFSET(dither.output_sample_bits), AV_OPT_TYPE_INT  , {.i64=0   }, 0      , 64        , PARAM },
+{ "clip_protection"     , "Clipping Protection"         , OFFSET(clip_protection), AV_OPT_TYPE_INT, { .i64 = 0 }, 0, 1, PARAM },
 {0}
 };
 
diff --git a/libswresample/rematrix.c b/libswresample/rematrix.c
index fb4d9aecf0..b095e2d34f 100644
--- a/libswresample/rematrix.c
+++ b/libswresample/rematrix.c
@@ -452,6 +452,7 @@ av_cold int swri_rematrix_init(SwrContext *s){
     int nb_out = s->out.ch_count;
 
     s->mix_any_f = NULL;
+    s->clip_max = 1.0f;
 
     if (!s->rematrix_custom) {
         int r = auto_matrix(s);
@@ -566,7 +567,7 @@ int swri_rematrix(SwrContext *s, AudioData *out, AudioData *in, int len, int mus
 
     if(s->mix_any_f) {
         s->mix_any_f(out->ch, (const uint8_t **)in->ch, s->native_matrix, len);
-        return 0;
+        goto clip_protection;
     }
 
     if(s->mix_2_1_simd || s->mix_1_1_simd){
@@ -637,5 +638,22 @@ int swri_rematrix(SwrContext *s, AudioData *out, AudioData *in, int len, int mus
             }
         }
     }
+
+clip_protection:
+    if (s->clip_protection && s->int_sample_fmt == AV_SAMPLE_FMT_FLTP)
+    {
+        for(j = 0; j < out->ch_count; j++) {
+            for(i = 0; i < len; i++) {
+                const float sample = fabsf(((float *)out->ch[j])[i]);
+                if (sample > s->clip_max) {
+                    s->clip_max = sample;
+                    av_log(s, AV_LOG_INFO, "Clipping protection at %.3f\n", sample);
+                }
+                if (s->clip_max > 1.0f)
+                    ((float *)out->ch[j])[i] /= s->clip_max;
+            }
+        }
+    }
+
     return 0;
 }
diff --git a/libswresample/swresample_internal.h b/libswresample/swresample_internal.h
index 7e46b16fb2..814b3ab888 100644
--- a/libswresample/swresample_internal.h
+++ b/libswresample/swresample_internal.h
@@ -183,6 +183,9 @@ struct SwrContext {
     mix_any_func_type *mix_any_f;
 
     /* TODO: callbacks for ASM optimizations */
+
+    int clip_protection;
+    float clip_max;
 };
 
 av_warn_unused_result