sws: add AVOption flag for error diffusion dither

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

libswscale/options.c

@@ -51,6 +51,7 @@ static const AVOption options[] = {
     { "full_chroma_int", "full chroma interpolation",     0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_FULL_CHR_H_INT }, INT_MIN, INT_MAX,        VE, "sws_flags" },
     { "full_chroma_inp", "full chroma input",             0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_FULL_CHR_H_INP }, INT_MIN, INT_MAX,        VE, "sws_flags" },
     { "bitexact",        "",                              0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_BITEXACT       }, INT_MIN, INT_MAX,        VE, "sws_flags" },
+    { "error_diffusion", "error diffusion dither",        0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_ERROR_DIFFUSION}, INT_MIN, INT_MAX,        VE, "sws_flags" },
 
     { "srcw",            "source width",                  OFFSET(srcW),      AV_OPT_TYPE_INT,    { .i64 = 16                 }, 1,       INT_MAX,        VE },
     { "srch",            "source height",                 OFFSET(srcH),      AV_OPT_TYPE_INT,    { .i64 = 16                 }, 1,       INT_MAX,        VE },