From 2b1ef029eb00731908dac044f409300b4b378c83 Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@haasn.dev>
Date: Wed, 13 Aug 2025 14:00:40 +0200
Subject: [PATCH] avfilter/vf_format: add alpha_modes parameter

---
 doc/filters.texi        |  4 ++++
 libavfilter/vf_format.c | 22 +++++++++++++++++++---
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/doc/filters.texi b/doc/filters.texi
index 3d6a9aff73..7efc7fa689 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -14307,6 +14307,10 @@ A '|'-separated list of color space names, such as
 A '|'-separated list of color range names, such as
 "color_ranges=tv|pc".
 
+@item alpha_modes
+A '|'-separated list of color range names, such as
+"alpha_modes=straight|premultiplied".
+
 @end table
 
 @subsection Examples
diff --git a/libavfilter/vf_format.c b/libavfilter/vf_format.c
index ae91b9655a..76d64bb4ae 100644
--- a/libavfilter/vf_format.c
+++ b/libavfilter/vf_format.c
@@ -42,10 +42,12 @@ typedef struct FormatContext {
     char *pix_fmts;
     char *csps;
     char *ranges;
+    char *alphamodes;
 
     AVFilterFormats *formats; ///< parsed from `pix_fmts`
     AVFilterFormats *color_spaces; ///< parsed from `csps`
     AVFilterFormats *color_ranges; ///< parsed from `ranges`
+    AVFilterFormats *alpha_modes; ///< parsed from `alphamodes`
 } FormatContext;
 
 static av_cold void uninit(AVFilterContext *ctx)
@@ -54,6 +56,7 @@ static av_cold void uninit(AVFilterContext *ctx)
     ff_formats_unref(&s->formats);
     ff_formats_unref(&s->color_spaces);
     ff_formats_unref(&s->color_ranges);
+    ff_formats_unref(&s->alpha_modes);
 }
 
 static av_cold int invert_formats(AVFilterFormats **fmts,
@@ -133,17 +136,28 @@ static av_cold int init(AVFilterContext *ctx)
             return ret;
     }
 
+    for (char *sep, *cur = s->alphamodes; cur; cur = sep) {
+        sep = strchr(cur, '|');
+        if (sep && *sep)
+            *sep++ = 0;
+        if ((ret = av_alpha_mode_from_name(cur)) < 0 ||
+            (ret = ff_add_format(&s->alpha_modes, ret)) < 0)
+            return ret;
+    }
+
     if (!strcmp(ctx->filter->name, "noformat")) {
         if ((ret = invert_formats(&s->formats,      ff_all_formats(AVMEDIA_TYPE_VIDEO))) < 0 ||
             (ret = invert_formats(&s->color_spaces, ff_all_color_spaces())) < 0 ||
-            (ret = invert_formats(&s->color_ranges, ff_all_color_ranges())) < 0)
+            (ret = invert_formats(&s->color_ranges, ff_all_color_ranges())) < 0 ||
+            (ret = invert_formats(&s->alpha_modes,  ff_all_alpha_modes())) < 0)
             return ret;
     }
 
     /* hold on to a ref for the lifetime of the filter */
     if (s->formats      && (ret = ff_formats_ref(s->formats,      &s->formats)) < 0 ||
         s->color_spaces && (ret = ff_formats_ref(s->color_spaces, &s->color_spaces)) < 0 ||
-        s->color_ranges && (ret = ff_formats_ref(s->color_ranges, &s->color_ranges)) < 0)
+        s->color_ranges && (ret = ff_formats_ref(s->color_ranges, &s->color_ranges)) < 0 ||
+        s->alpha_modes  && (ret = ff_formats_ref(s->alpha_modes,  &s->alpha_modes)) < 0)
         return ret;
 
     return 0;
@@ -158,7 +172,8 @@ static int query_formats(const AVFilterContext *ctx,
 
     if (s->formats      && (ret = ff_set_common_formats2     (ctx, cfg_in, cfg_out, s->formats)) < 0 ||
         s->color_spaces && (ret = ff_set_common_color_spaces2(ctx, cfg_in, cfg_out, s->color_spaces)) < 0 ||
-        s->color_ranges && (ret = ff_set_common_color_ranges2(ctx, cfg_in, cfg_out, s->color_ranges)) < 0)
+        s->color_ranges && (ret = ff_set_common_color_ranges2(ctx, cfg_in, cfg_out, s->color_ranges)) < 0 ||
+        s->alpha_modes  && (ret = ff_set_common_alpha_modes2(ctx, cfg_in, cfg_out, s->alpha_modes)) < 0)
         return ret;
 
     return 0;
@@ -170,6 +185,7 @@ static const AVOption options[] = {
     { "pix_fmts", "A '|'-separated list of pixel formats", OFFSET(pix_fmts), AV_OPT_TYPE_STRING, .flags = AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
     { "color_spaces", "A '|'-separated list of color spaces", OFFSET(csps), AV_OPT_TYPE_STRING, .flags = AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
     { "color_ranges", "A '|'-separated list of color ranges", OFFSET(ranges), AV_OPT_TYPE_STRING, .flags = AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
+    { "alpha_modes", "A '|'-separated list of alpha modes", OFFSET(alphamodes), AV_OPT_TYPE_STRING, .flags = AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_FILTERING_PARAM },
     { NULL }
 };