[FFmpeg-devel] [PATCH] swscale/options: use accurate rounding and full chroma by default - rcombs via ffmpeg-devel

From: rcombs via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Cc: rcombs <rcombs@rcombs.me>
Subject: [FFmpeg-devel] [PATCH] swscale/options: use accurate rounding and full chroma by default
Date: Sun,  8 Jun 2025 14:23:40 -0700
Message-ID: <mailman.2596.1749417834.1384.ffmpeg-devel@ffmpeg.org> (raw)

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From: rcombs <rcombs@rcombs.me>
To: ffmpeg-devel@ffmpeg.org
Subject: [PATCH] swscale/options: use accurate rounding and full chroma by default
Date: Sun,  8 Jun 2025 14:23:40 -0700
Message-ID: <20250608212340.37328-1-rcombs@rcombs.me>

This has been causing quality degradation for people since the dawn of sws,
and the performance concerns that originally led to this default have been
soundly defeated by the march of time.
---
 doc/APIchanges       | 3 +++
 libswscale/options.c | 4 +++-
 libswscale/version.h | 2 +-
 3 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/doc/APIchanges b/doc/APIchanges
index 91710bb27d..6d81048e48 100644
--- a/doc/APIchanges
+++ b/doc/APIchanges
@@ -2,6 +2,9 @@ The last version increases of all libraries were on 2025-03-28
 
 API changes, most recent first:
 
+2024-12-xx - xxxxxxxxxx - lsws 9.0.101 - swscale.h
+  Use accurate rounding and full chroma by default.
+
 2025-05-21 - xxxxxxxxxx - lavu 60.3.100 - avassert.h
   Add av_unreachable() and av_assume() macros.
 
diff --git a/libswscale/options.c b/libswscale/options.c
index feecae8c89..7d29a416cb 100644
--- a/libswscale/options.c
+++ b/libswscale/options.c
@@ -31,8 +31,10 @@ static const char *sws_context_to_name(void *ptr)
 #define DEFAULT 0
 #define VE AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
 
+#define DEFAULT_FLAGS SWS_BICUBIC | SWS_ACCURATE_RND | SWS_FULL_CHR_H_INT | SWS_FULL_CHR_H_INP
+
 static const AVOption swscale_options[] = {
-    { "sws_flags",           "swscale flags",     OFFSET(flags),  AV_OPT_TYPE_FLAGS, { .i64 = SWS_BICUBIC        }, .flags = VE, .unit = "sws_flags", .max = UINT_MAX },
+    { "sws_flags",           "swscale flags",     OFFSET(flags),  AV_OPT_TYPE_FLAGS, { .i64 = DEFAULT_FLAGS      }, .flags = VE, .unit = "sws_flags", .max = UINT_MAX },
         { "fast_bilinear",   "fast bilinear",                 0,  AV_OPT_TYPE_CONST, { .i64 = SWS_FAST_BILINEAR  }, .flags = VE, .unit = "sws_flags" },
         { "bilinear",        "bilinear",                      0,  AV_OPT_TYPE_CONST, { .i64 = SWS_BILINEAR       }, .flags = VE, .unit = "sws_flags" },
         { "bicubic",         "bicubic",                       0,  AV_OPT_TYPE_CONST, { .i64 = SWS_BICUBIC        }, .flags = VE, .unit = "sws_flags" },
diff --git a/libswscale/version.h b/libswscale/version.h
index 148efd83eb..02baedad5b 100644
--- a/libswscale/version.h
+++ b/libswscale/version.h
@@ -29,7 +29,7 @@
 #include "version_major.h"
 
 #define LIBSWSCALE_VERSION_MINOR   0
-#define LIBSWSCALE_VERSION_MICRO 100
+#define LIBSWSCALE_VERSION_MICRO 101
 
 #define LIBSWSCALE_VERSION_INT  AV_VERSION_INT(LIBSWSCALE_VERSION_MAJOR, \
                                                LIBSWSCALE_VERSION_MINOR, \
-- 
2.45.1


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