swscale: make bilinear scaling the default

Before this commit, sws_init_context() failed with an error if no scaler
was explicitly set.

Defaulting to something reasonable is better behavior.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/options.c

@@ -34,7 +34,7 @@ static const char *sws_context_to_name(void *ptr)
 #define VE AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
 
 static const AVOption swscale_options[] = {
-    { "sws_flags",       "scaler flags",                  OFFSET(flags),     AV_OPT_TYPE_FLAGS,  { .i64 = DEFAULT            }, 0,       UINT_MAX,       VE, "sws_flags" },
+    { "sws_flags",       "scaler flags",                  OFFSET(flags),     AV_OPT_TYPE_FLAGS,  { .i64  = SWS_BILINEAR       }, 0,       UINT_MAX,       VE, "sws_flags" },
     { "fast_bilinear",   "fast bilinear",                 0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_FAST_BILINEAR  }, INT_MIN, INT_MAX,        VE, "sws_flags" },
     { "bilinear",        "bilinear",                      0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_BILINEAR       }, INT_MIN, INT_MAX,        VE, "sws_flags" },
     { "bicubic",         "bicubic",                       0,                 AV_OPT_TYPE_CONST,  { .i64  = SWS_BICUBIC        }, INT_MIN, INT_MAX,        VE, "sws_flags" },