vc2enc: use 32x16 slices by default

Approximately 1.25 times faster than 64x32, visually and
statistically improves quality.
Signed-off-by: Rostislav Pehlivanov <atomnuker@gmail.com>

libavcodec/vc2enc.c

@@ -1234,8 +1234,8 @@ alloc_fail:
 #define VC2ENC_FLAGS (AV_OPT_FLAG_ENCODING_PARAM | AV_OPT_FLAG_VIDEO_PARAM)
 static const AVOption vc2enc_options[] = {
     {"tolerance",     "Max undershoot in percent", offsetof(VC2EncContext, tolerance), AV_OPT_TYPE_DOUBLE, {.dbl = 5.0f}, 0.0f, 45.0f, VC2ENC_FLAGS, "tolerance"},
-    {"slice_width",   "Slice width",  offsetof(VC2EncContext, slice_width), AV_OPT_TYPE_INT, {.i64 = 64}, 32, 1024, VC2ENC_FLAGS, "slice_width"},
-    {"slice_height",  "Slice height", offsetof(VC2EncContext, slice_height), AV_OPT_TYPE_INT, {.i64 = 32}, 8, 1024, VC2ENC_FLAGS, "slice_height"},
+    {"slice_width",   "Slice width",  offsetof(VC2EncContext, slice_width), AV_OPT_TYPE_INT, {.i64 = 32}, 32, 1024, VC2ENC_FLAGS, "slice_width"},
+    {"slice_height",  "Slice height", offsetof(VC2EncContext, slice_height), AV_OPT_TYPE_INT, {.i64 = 16}, 8, 1024, VC2ENC_FLAGS, "slice_height"},
     {"wavelet_depth", "Transform depth", offsetof(VC2EncContext, wavelet_depth), AV_OPT_TYPE_INT, {.i64 = 4}, 1, 5, VC2ENC_FLAGS, "wavelet_depth"},
     {"wavelet_type",  "Transform type",  offsetof(VC2EncContext, wavelet_idx), AV_OPT_TYPE_INT, {.i64 = VC2_TRANSFORM_9_7}, 0, VC2_TRANSFORMS_NB, VC2ENC_FLAGS, "wavelet_idx"},
         {"9_7",          "Deslauriers-Dubuc (9,7)", 0, AV_OPT_TYPE_CONST, {.i64 = VC2_TRANSFORM_9_7},    INT_MIN, INT_MAX, VC2ENC_FLAGS, "wavelet_idx"},