swr: add triangular dither support

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswresample/dither.c

@@ -40,6 +40,11 @@ void swri_get_dither(void *dst, int len, unsigned seed, enum AVSampleFormat out_
 
         switch(method){
             case SWR_DITHER_RECTANGULAR: v= ((double)seed) / UINT_MAX - 0.5; break;
+            case SWR_DITHER_TRIANGULAR :
+                v = ((double)seed) / UINT_MAX;
+                seed = seed*1664525 + 1013904223;
+                v-= ((double)seed) / UINT_MAX;
+                break;
             default: av_assert0(0);
         }
 

libswresample/swresample.c

@@ -55,6 +55,7 @@ static const AVOption options[]={
 {"res", "force resampling", 0, AV_OPT_TYPE_CONST, {.dbl=SWR_FLAG_RESAMPLE}, INT_MIN, INT_MAX, 0, "flags"},
 {"dither", "dither method"      , OFFSET(dither_method), AV_OPT_TYPE_INT, {.dbl=0}, 0, SWR_DITHER_NB-1, 0, "dither_method"},
 {"rectangular", "rectangular dither", 0, AV_OPT_TYPE_CONST, {.dbl=SWR_DITHER_RECTANGULAR}, INT_MIN, INT_MAX, 0, "dither_method"},
+{"triangular" , "triangular dither" , 0, AV_OPT_TYPE_CONST, {.dbl=SWR_DITHER_TRIANGULAR }, INT_MIN, INT_MAX, 0, "dither_method"},
 
 {0}
 };

libswresample/swresample.h

@@ -48,6 +48,7 @@
 enum SwrDitherType {
     SWR_DITHER_NONE = 0,
     SWR_DITHER_RECTANGULAR,
+    SWR_DITHER_TRIANGULAR,
     SWR_DITHER_NB,              ///< not part of API/ABI
 };