avresample: 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.

3 files changed, 23 insertions, 0 deletions

diff --git a/libavresample/audio_mix.c b/libavresample/audio_mix.c
index 7ae0aeb74d..ae1a09b892 100644
--- a/libavresample/audio_mix.c
+++ b/libavresample/audio_mix.c
@@ -56,6 +56,9 @@ struct AudioMix {
     int32_t *matrix_q15[AVRESAMPLE_MAX_CHANNELS];
     float   *matrix_flt[AVRESAMPLE_MAX_CHANNELS];
     void   **matrix;
+
+    int clip_protection;
+    float clip_max;
 };
 
 void ff_audio_mix_set_func(AudioMix *am, enum AVSampleFormat fmt,
@@ -362,6 +365,8 @@ AudioMix *ff_audio_mix_alloc(AVAudioResampleContext *avr)
     am->out_layout   = avr->out_channel_layout;
     am->in_channels  = avr->in_channels;
     am->out_channels = avr->out_channels;
+    am->clip_protection = avr->internal_sample_fmt == AV_SAMPLE_FMT_FLTP && avr->clip_protection;
+    am->clip_max     = 1.0f;
 
     /* build matrix if the user did not already set one */
     if (avr->mix_matrix) {
@@ -477,6 +482,21 @@ int ff_audio_mix(AudioMix *am, AudioData *src)
 
     ff_audio_data_set_channels(src, am->out_channels);
 
+    /* clip protection is only enabled when the internal sample format is fltp, so we don't need to check here */
+    if (am->clip_protection) {
+        for(i = 0; i < src->nb_samples; i++) {
+            for (j = 0; j < src->channels; j++) {
+                const float sample = fabs(((float **)src->data)[j][i]);
+                if (sample > am->clip_max) {
+                    am->clip_max = sample;
+                    av_log(am->avr, AV_LOG_INFO, "Clipping protection at %.3f\n", sample);
+                }
+                if (am->clip_max > 1.0f)
+                    ((float **)src->data)[j][i] /= am->clip_max;
+            }
+        }
+    }
+
     return 0;
 }
 
diff --git a/libavresample/internal.h b/libavresample/internal.h
index 2fc3f6da67..815be824a8 100644
--- a/libavresample/internal.h
+++ b/libavresample/internal.h
@@ -105,6 +105,8 @@ struct AVAudioResampleContext {
     int use_channel_map;
     enum RemapPoint remap_point;
     ChannelMapInfo ch_map_info;
+
+    int clip_protection;
 };
 
 
diff --git a/libavresample/options.c b/libavresample/options.c
index 5f08cd7e52..23575238f1 100644
--- a/libavresample/options.c
+++ b/libavresample/options.c
@@ -83,6 +83,7 @@ static const AVOption avresample_options[] = {
         {"triangular",    "Triangular Dither",                    0, AV_OPT_TYPE_CONST, { .i64 = AV_RESAMPLE_DITHER_TRIANGULAR    }, INT_MIN, INT_MAX, PARAM, "dither_method"},
         {"triangular_hp", "Triangular Dither With High Pass",     0, AV_OPT_TYPE_CONST, { .i64 = AV_RESAMPLE_DITHER_TRIANGULAR_HP }, INT_MIN, INT_MAX, PARAM, "dither_method"},
         {"triangular_ns", "Triangular Dither With Noise Shaping", 0, AV_OPT_TYPE_CONST, { .i64 = AV_RESAMPLE_DITHER_TRIANGULAR_NS }, INT_MIN, INT_MAX, PARAM, "dither_method"},
+    { "clip_protection",        "Clipping Protection",      OFFSET(clip_protection),        AV_OPT_TYPE_INT,    { .i64 = 0              }, 0,                    1,                      PARAM },
     { NULL },
 };