From 38a5fcc02c2ef1bcb37d2e53eddde8eccc0c75ed Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@haasn.dev>
Date: Wed, 24 Sep 2025 15:23:04 +0200
Subject: [PATCH] fftools/ffmpeg_filter: close all no-longer needed inputs

Currently, the thread loop of ffmpeg_filter essentially works like this:

while (1) {
    frame, idx = get_from_decoder();
    err = send_to_filter_graph(frame);
    if (err) { // i.e. EOF
        close_input(idx);
        continue;
    }

    while (filtered_frame = get_filtered_frame())
        send_to_encoder(filtered_frame);
}

The exact details are not 100% correct since the actual control flow is a bit
more complicated as a result of the scheduler, but this is the general flow.

Notably, this leaves the possibility of leaving a no-longer-needed input
permanently open if the filter graph starts producing infinite frames (during
the second loop) *after* it finishes reading from an input, e.g. in a filter
graph like -af atrim,apad.

This patch avoids this issue by always querying the status of all filter graph
inputs and explicitly closing any that were closed downstream; after each round
of reading output frames. As a result, information about the filtergraph being
closed can now propagate back upstream, even if the filter is no longer
requesting any input frames (i.e. input_idx == fg->nb_inputs).

Fixes: https://trac.ffmpeg.org/ticket/11061
See-Also: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/20457#issuecomment-6208
---
 fftools/ffmpeg_filter.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fftools/ffmpeg_filter.c b/fftools/ffmpeg_filter.c
index 9f962e6b8c..d5ae59ec03 100644
--- a/fftools/ffmpeg_filter.c
+++ b/fftools/ffmpeg_filter.c
@@ -2616,6 +2616,16 @@ finish:
     fps->dropped_keyframe |= fps->last_dropped && (frame->flags & AV_FRAME_FLAG_KEY);
 }
 
+static void close_input(InputFilterPriv *ifp)
+{
+    FilterGraphPriv *fgp = fgp_from_fg(ifp->ifilter.graph);
+
+    if (!ifp->eof) {
+        sch_filter_receive_finish(fgp->sch, fgp->sch_idx, ifp->ifilter.index);
+        ifp->eof = 1;
+    }
+}
+
 static int close_output(OutputFilterPriv *ofp, FilterGraphThread *fgt)
 {
     FilterGraphPriv *fgp = fgp_from_fg(ofp->ofilter.graph);
@@ -3343,7 +3353,7 @@ static int filter_thread(void *arg)
         if (ret == AVERROR_EOF) {
             av_log(fg, AV_LOG_VERBOSE, "Input %u no longer accepts new data\n",
                    input_idx);
-            sch_filter_receive_finish(fgp->sch, fgp->sch_idx, input_idx);
+            close_input(ifp);
             continue;
         }
         if (ret < 0)
@@ -3362,6 +3372,13 @@ read_frames:
                    av_err2str(ret));
             goto finish;
         }
+
+        // ensure all inputs no longer accepting data are closed
+        for (int i = 0; fgt.graph && i < fg->nb_inputs; i++) {
+            InputFilterPriv *ifp = ifp_from_ifilter(fg->inputs[i]);
+            if (av_buffersrc_get_status(ifp->ifilter.filter))
+                close_input(ifp);
+        }
     }
 
     for (unsigned i = 0; i < fg->nb_outputs; i++) {