libx264: Make sure to preserve default option values

The private options chromaoffset, sc_threshold, and noise_reduction
were set to 0 rather than -1, and were always initializing values
in libx264 rather than letting the library use its default.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/libx264.c

@@ -536,12 +536,11 @@ static av_cold int X264_init(AVCodecContext *avctx)
 
 #if FF_API_PRIVATE_OPT
 FF_DISABLE_DEPRECATION_WARNINGS
-    if (avctx->chromaoffset)
+    if (avctx->chromaoffset >= 0)
         x4->chroma_offset = avctx->chromaoffset;
 FF_ENABLE_DEPRECATION_WARNINGS
 #endif
-
-    if (x4->chroma_offset)
+    if (x4->chroma_offset >= 0)
         x4->params.analyse.i_chroma_qp_offset = x4->chroma_offset;
 
     if (avctx->gop_size >= 0)
@@ -989,9 +988,9 @@ static const AVOption options[] = {
     { "vlc",              NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 0 },  INT_MIN, INT_MAX, VE, "coder" },
     { "ac",               NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 1 },  INT_MIN, INT_MAX, VE, "coder" },
     { "b_strategy",   "Strategy to choose between I/P/B-frames",          OFFSET(b_frame_strategy), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 2, VE },
-    { "chromaoffset", "QP difference between chroma and luma",           OFFSET(chroma_offset), AV_OPT_TYPE_INT, { .i64 = 0 }, INT_MIN, INT_MAX, VE },
-    { "sc_threshold", "Scene change threshold",                           OFFSET(scenechange_threshold), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE },
-    { "noise_reduction", "Noise reduction",                               OFFSET(noise_reduction), AV_OPT_TYPE_INT, { .i64 = -1 }, 0, INT_MAX, VE },
+    { "chromaoffset", "QP difference between chroma and luma",            OFFSET(chroma_offset), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX, VE },
+    { "sc_threshold", "Scene change threshold",                           OFFSET(scenechange_threshold), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX, VE },
+    { "noise_reduction", "Noise reduction",                               OFFSET(noise_reduction), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX, VE },
 
     { "x264-params",  "Override the x264 configuration using a :-separated list of key=value parameters", OFFSET(x264_params), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE },
     { NULL },