[FFmpeg-devel] [PATCH v2 18/18] avfilter/vf_libplacebo: add an alpha_mode setting

[Niklas Haas <ffmpeg@haasn.xyz>]

From: Niklas Haas <git@haasn.dev>

Chooses the desired output alpha mode. Note that this depends on
an upstream version of libplacebo new enough to respect the corresponding
AVFrame field in pl_map_avframe_ex.
---
 doc/filters.texi            |  4 ++++
 libavfilter/vf_libplacebo.c | 13 +++++++++++++
 2 files changed, 17 insertions(+)

diff --git a/doc/filters.texi b/doc/filters.texi
index 13ca065f85..d4566cb594 100644
--- a/doc/filters.texi
+++ b/doc/filters.texi
@@ -16380,6 +16380,10 @@ leading to no change. For any other value, conversion will be performed.
 
 See the @ref{setparams} filter for a list of possible values.
 
+@item alpha_mode
+Choose the desired output alpha mode, when the output format has an alpha
+channel. See the @ref{setparams} filter for a list of possible values.
+
 @item apply_filmgrain
 Apply film grain (e.g. AV1 or H.274) if present in source frames, and strip
 it from the output. Enabled by default.
diff --git a/libavfilter/vf_libplacebo.c b/libavfilter/vf_libplacebo.c
index 475030c80d..bb73350da5 100644
--- a/libavfilter/vf_libplacebo.c
+++ b/libavfilter/vf_libplacebo.c
@@ -195,6 +195,7 @@ typedef struct LibplaceboContext {
     int color_primaries;
     int color_trc;
     int rotation;
+    int alpha_mode;
     AVDictionary *extra_opts;
 
 #if PL_API_VER >= 351
@@ -920,6 +921,11 @@ static int output_frame(AVFilterContext *ctx, int64_t pts)
     if (s->color_primaries >= 0)
         out->color_primaries = s->color_primaries;
 
+    if (outdesc->flags & AV_PIX_FMT_FLAG_ALPHA) {
+        if (s->alpha_mode >= 0)
+            out->alpha_mode = s->alpha_mode;
+    }
+
     /* Strip side data if no longer relevant */
     if (out->width != ref->width || out->height != ref->height)
         changed |= AV_SIDE_DATA_PROP_SIZE_DEPENDENT;
@@ -1475,6 +1481,13 @@ static const AVOption libplacebo_options[] = {
     {"270",                            NULL,  0, AV_OPT_TYPE_CONST, {.i64=PL_ROTATION_270}, .flags = STATIC, .unit = "rotation"},
     {"360",                            NULL,  0, AV_OPT_TYPE_CONST, {.i64=PL_ROTATION_360}, .flags = STATIC, .unit = "rotation"},
 
+    {"alpha_mode", "select alpha moda", OFFSET(alpha_mode), AV_OPT_TYPE_INT, {.i64=-1}, -1, AVALPHA_MODE_NB-1, DYNAMIC, .unit = "alpha_mode"},
+    {"auto", "keep the same alpha mode",  0, AV_OPT_TYPE_CONST, {.i64=-1},                              0, 0, DYNAMIC, .unit = "alpha_mode"},
+    {"unspecified",                      NULL, 0, AV_OPT_TYPE_CONST, {.i64=AVALPHA_MODE_UNSPECIFIED},   0, 0, DYNAMIC, .unit = "alpha_mode"},
+    {"unknown",                          NULL, 0, AV_OPT_TYPE_CONST, {.i64=AVALPHA_MODE_UNSPECIFIED},   0, 0, DYNAMIC, .unit = "alpha_mode"},
+    {"premultiplied",                    NULL, 0, AV_OPT_TYPE_CONST, {.i64=AVALPHA_MODE_PREMULTIPLIED}, 0, 0, DYNAMIC, .unit = "alpha_mode"},
+    {"straight",                         NULL, 0, AV_OPT_TYPE_CONST, {.i64=AVALPHA_MODE_STRAIGHT},      0, 0, DYNAMIC, .unit = "alpha_mode"},
+
     { "upscaler", "Upscaler function", OFFSET(upscaler), AV_OPT_TYPE_STRING, {.str = "spline36"}, .flags = DYNAMIC },
     { "downscaler", "Downscaler function", OFFSET(downscaler), AV_OPT_TYPE_STRING, {.str = "mitchell"}, .flags = DYNAMIC },
     { "frame_mixer", "Frame mixing function", OFFSET(frame_mixer), AV_OPT_TYPE_STRING, {.str = "none"}, .flags = DYNAMIC },
-- 
2.50.1

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