swresample: Skip over dither steps if dithering scale is 0

Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libswresample/dither.c

@@ -102,6 +102,11 @@ av_cold int swri_dither_init(SwrContext *s, enum AVSampleFormat out_fmt, enum AV
     if (out_fmt == AV_SAMPLE_FMT_S32 && s->dither.output_sample_bits)
         scale *= 1<<(32-s->dither.output_sample_bits);
 
+    if (scale == 0) {
+        s->dither.method = 0;
+        return 0;
+    }
+
     s->dither.ns_pos = 0;
     s->dither.noise_scale=   scale;
     s->dither.ns_scale   =   scale;

libswresample/options.c

@@ -70,7 +70,7 @@ static const AVOption options[]={
 
 {"dither_scale"         , "set dither scale"            , OFFSET(dither.scale   ), AV_OPT_TYPE_FLOAT, {.dbl=1                     }, 0      , INT_MAX   , PARAM},
 
-{"dither_method"        , "set dither method"           , OFFSET(dither.method  ), AV_OPT_TYPE_INT  , {.i64=0                     }, 0      , SWR_DITHER_NB-1, PARAM, "dither_method"},
+{"dither_method"        , "set dither method"           , OFFSET(user_dither_method),AV_OPT_TYPE_INT, {.i64=0                     }, 0      , SWR_DITHER_NB-1, PARAM, "dither_method"},
 {"rectangular"          , "select rectangular dither"   , 0                      , AV_OPT_TYPE_CONST, {.i64=SWR_DITHER_RECTANGULAR}, INT_MIN, INT_MAX   , PARAM, "dither_method"},
 {"triangular"           , "select triangular dither"    , 0                      , AV_OPT_TYPE_CONST, {.i64=SWR_DITHER_TRIANGULAR }, INT_MIN, INT_MAX   , PARAM, "dither_method"},
 {"triangular_hp"        , "select triangular dither with high pass" , 0          , AV_OPT_TYPE_CONST, {.i64=SWR_DITHER_TRIANGULAR_HIGHPASS }, INT_MIN, INT_MAX, PARAM, "dither_method"},

libswresample/swresample.c

@@ -176,6 +176,8 @@ av_cold int swr_init(struct SwrContext *s){
 
     s->int_sample_fmt= s->user_int_sample_fmt;
 
+    s->dither.method = s->user_dither_method;
+
     if(av_get_channel_layout_nb_channels(s-> in_ch_layout) > SWR_CH_MAX) {
         av_log(s, AV_LOG_WARNING, "Input channel layout 0x%"PRIx64" is invalid or unsupported.\n", s-> in_ch_layout);
         s->in_ch_layout = 0;

libswresample/swresample_internal.h

@@ -120,6 +120,7 @@ struct SwrContext {
     int64_t user_in_ch_layout;                      ///< User set input channel layout
     int64_t user_out_ch_layout;                     ///< User set output channel layout
     enum AVSampleFormat user_int_sample_fmt;        ///< User set internal sample format
+    int user_dither_method;                         ///< User set dither method
 
     struct DitherContext dither;