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fftools/ffmpeg_filter: close all no-longer needed inputs

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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
This commit is contained in:
Niklas Haas
2025-09-24 15:23:04 +02:00
committed by Niklas Haas
parent 623669a02c
commit 38a5fcc02c
1 changed files with 18 additions and 1 deletions
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19
fftools/ffmpeg_filter.c
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@@ -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++) {