[FFmpeg-devel] [PATCH] release/8.0: avfilter/feedback: fix feedback block (PR #21201)

[Jack Lau via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21201 opened by Jack Lau (JackLau)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21201
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21201.patch

Fix #20940

The feedback and its sub-filter both request frame
from each other, casuing block since 4440e499ba

The feedback should only request inputs[1] once
rather than continuously request frame cause blocking.

This patch add check whether feedback already request
inputs[1] via ff_outlink_frame_wanted(ctx->outputs[1]),
if true, then exit and waiting inputs[0] because it means
we need more frames input to proceed.

Signed-off-by: Jack Lau <jacklau1222gm@gmail.com>
(cherry picked from commit 3f0842294fbefcca32fdad6b644eae8c14f547e5)


>From 2333984d846186f69806a886b12cf5efeebfecc1 Mon Sep 17 00:00:00 2001
From: Jack Lau <jacklau1222gm@gmail.com>
Date: Tue, 18 Nov 2025 06:45:06 +0800
Subject: [PATCH] avfilter/vf_feedback: fix feedback block

Fix #20940

The feedback and its sub-filter both request frame
from each other, casuing block since 4440e499ba

The feedback should only request inputs[1] once
rather than continuously request frame cause blocking.

This patch add check whether feedback already request
inputs[1] via ff_outlink_frame_wanted(ctx->outputs[1]),
if true, then exit and waiting inputs[0] because it means
we need more frames input to proceed.

Signed-off-by: Jack Lau <jacklau1222gm@gmail.com>
(cherry picked from commit 3f0842294fbefcca32fdad6b644eae8c14f547e5)
---
 libavfilter/vf_feedback.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libavfilter/vf_feedback.c b/libavfilter/vf_feedback.c
index 6667ddfd16..e3633d7d37 100644
--- a/libavfilter/vf_feedback.c
+++ b/libavfilter/vf_feedback.c
@@ -245,6 +245,10 @@ static int activate(AVFilterContext *ctx)
     }
 
     if (!s->feed || ctx->is_disabled) {
+        if (!ctx->is_disabled && ff_outlink_frame_wanted(ctx->outputs[1])) {
+            ff_inlink_request_frame(ctx->inputs[0]);
+            return 0;
+        }
         if (ff_outlink_frame_wanted(ctx->outputs[0])) {
             ff_inlink_request_frame(ctx->inputs[0]);
             if (!ctx->is_disabled)
-- 
2.49.1

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