[FFmpeg-devel] [PATCH] avfilter/vf_libplacebo: fix possible segfault when frame mixing (PR #20211)

[Niklas Haas <code@ffmpeg.org>]

PR #20211 opened by Niklas Haas (haasn)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20211
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20211.patch

pl_frame_mix_current() will return NULL if all frames are in the future,
but when libplacebo is using a frame mixer with a radius greater than 1,
future frames are expected to already be partially renderered. Instead, use
pl_frame_mix_nearest(), which is guaranteed to give us a valid frame for any
nonempty frame mix.

Fixes: 3091bca3edb339a4d2ec8c64e52fa7e67a7d5005


From 5d70dc27c0198dbcf9843efd2145189cb0a89d26 Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@haasn.dev>
Date: Mon, 11 Aug 2025 09:58:58 +0200
Subject: [PATCH] avfilter/vf_libplacebo: fix possible segfault when frame
 mixing

pl_frame_mix_current() will return NULL if all frames are in the future,
but when libplacebo is using a frame mixer with a radius greater than 1,
future frames are expected to already be partially renderered. Instead, use
pl_frame_mix_nearest(), which is guaranteed to give us a valid frame for any
nonempty frame mix.

Fixes: 3091bca3edb339a4d2ec8c64e52fa7e67a7d5005
---
 libavfilter/vf_libplacebo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/libavfilter/vf_libplacebo.c b/libavfilter/vf_libplacebo.c
index 135749d3b1..01ce9d56b7 100644
--- a/libavfilter/vf_libplacebo.c
+++ b/libavfilter/vf_libplacebo.c
@@ -928,7 +928,8 @@ static int output_frame(AVFilterContext *ctx, int64_t pts)
         struct pl_frame dummy;
         if (in->qstatus != PL_QUEUE_OK || !in->mix.num_frames)
             continue;
-        const struct pl_frame *cur = pl_frame_mix_current(&in->mix);
+        const struct pl_frame *cur = pl_frame_mix_nearest(&in->mix);
+        av_assert1(cur);
         update_crops(ctx, in, &dummy, target_pts);
         const int x0 = roundf(FFMIN(dummy.crop.x0, dummy.crop.x1)),
                   y0 = roundf(FFMIN(dummy.crop.y0, dummy.crop.y1)),
-- 
2.49.1

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