From: Niklas Haas <ffmpeg@haasn.xyz>
To: ffmpeg-devel@ffmpeg.org
Cc: Niklas Haas <git@haasn.dev>
Subject: [FFmpeg-devel] [PATCH] avfilter/vf_libplacebo: set correct alpha mode before blending
Date: Thu, 20 Feb 2025 14:41:50 +0100
Message-ID: <20250220134150.274215-1-ffmpeg@haasn.xyz> (raw)
From: Niklas Haas <git@haasn.dev>
&pl_alpha_overlay expects straight alpha, but the alpha output may be
premultiplied as a result of the target alpha mode (or in the absence of an
alpha channel). Fix it by requesting independent alpha explicitly when
blending.
---
libavfilter/vf_libplacebo.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/libavfilter/vf_libplacebo.c b/libavfilter/vf_libplacebo.c
index f6c29c2f2b..28a0bde135 100644
--- a/libavfilter/vf_libplacebo.c
+++ b/libavfilter/vf_libplacebo.c
@@ -909,6 +909,9 @@ static int output_frame(AVFilterContext *ctx, int64_t pts)
opts->params.skip_caching_single_frame = high_fps;
update_crops(ctx, in, &target, out->pts * av_q2d(outlink->time_base));
pl_render_image_mix(in->renderer, &in->mix, &target, &opts->params);
+
+ /* Force straight output and set correct blend mode */
+ target.repr.alpha = PL_ALPHA_INDEPENDENT;
opts->params.blend_params = &pl_alpha_overlay;
#if PL_API_VER >= 346
opts->params.background = opts->params.border = PL_CLEAR_SKIP;
--
2.47.0
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reply other threads:[~2025-02-20 13:42 UTC|newest]
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