[FFmpeg-devel] [PATCH] avfilter/avfiltergraph: always retry format negotiation after auto-filters (PR #21100)

[Niklas Haas via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21100 opened by Niklas Haas (haasn)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21100
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21100.patch

There is an edge case not covered by the current logic: If there is only
a single auto-filter inserted, but the auto-inserted filter is incompatible
with a *different* format attribute (after settling the previous formats),
we may need a second auto-filter (e.g. `scale`) to settle the newly introduced
incompatibility.

A regression test demonstrating the issue is added.


>From 60a3b0848e038d75a59dd942c547787c6e68869a Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@haasn.dev>
Date: Thu, 4 Dec 2025 13:25:03 +0100
Subject: [PATCH 1/2] avfilter/avfiltergraph: always retry format negotiation
 after auto-filters

There is an edge case not covered by the current logic: If there is only
a single auto-filter inserted, but the auto-inserted filter is incompatible
with a *different* format attribute (after settling the previous formats),
we may need a second auto-filter (e.g. `scale`) to settle the newly introduced
incompatibility.

A regression test demonstrating the issue is added.
---
 libavfilter/avfiltergraph.c             |  9 +++++----
 tests/fate/filter-video.mak             |  3 +++
 tests/ref/fate/filter-scale-premultiply | 15 +++++++++++++++
 3 files changed, 23 insertions(+), 4 deletions(-)
 create mode 100644 tests/ref/fate/filter-scale-premultiply

diff --git a/libavfilter/avfiltergraph.c b/libavfilter/avfiltergraph.c
index d5c2ef54e6..c15d95b91e 100644
--- a/libavfilter/avfiltergraph.c
+++ b/libavfilter/avfiltergraph.c
@@ -701,10 +701,11 @@ retry:
                 }
             }
 
-            /* if there is more than one auto filter, we may need another round
-             * to fully settle formats due to possible cross-incompatibilities
-             * between the auto filters themselves */
-            if (num_conv > 1)
+            /* if there is an auto filter, we may need another round to fully
+             * settle formats due to possible cross-incompatibilities between
+             * the auto filters themselves, or between the auto filters and
+             * a different attribute of the filter they are modifying */
+            if (num_conv)
                 goto retry;
         }
     }
diff --git a/tests/fate/filter-video.mak b/tests/fate/filter-video.mak
index 9f3c92a395..35b2687b27 100644
--- a/tests/fate/filter-video.mak
+++ b/tests/fate/filter-video.mak
@@ -836,6 +836,9 @@ FATE_FILTER-$(call ALLYES, TESTSRC2_FILTER SPLIT_FILTER AVGBLUR_FILTER        \
                            METADATA_FILTER WRAPPED_AVFRAME_ENCODER NULL_MUXER \
                            PIPE_PROTOCOL) += $(FATE_FILTER_REFCMP_METADATA-yes)
 
+FATE_FILTER-$(call FILTERFRAMECRC, TESTSRC SCALE PREMULTIPLY, LAVFI_INDEV) += fate-filter-scale-premultiply
+fate-filter-scale-premultiply: CMD = framecrc -auto_conversion_filters -lavfi "testsrc,format=rgba,setparams=alpha_mode=premultiplied,format=rgba:alpha_modes=straight" -frames:v 10
+
 FATE_SAMPLES_FFPROBE += $(FATE_METADATA_FILTER-yes)
 FATE_SAMPLES_FFMPEG += $(FATE_FILTER_SAMPLES-yes)
 FATE_FFPROBE += $(FATE_FILTER_FFPROBE-yes)
diff --git a/tests/ref/fate/filter-scale-premultiply b/tests/ref/fate/filter-scale-premultiply
new file mode 100644
index 0000000000..13fd79310a
--- /dev/null
+++ b/tests/ref/fate/filter-scale-premultiply
@@ -0,0 +1,15 @@
+#tb 0: 1/25
+#media_type 0: video
+#codec_id 0: rawvideo
+#dimensions 0: 320x240
+#sar 0: 1/1
+0,          0,          0,        1,   307200, 0x73a3b71f
+0,          1,          1,        1,   307200, 0x3f05f047
+0,          2,          2,        1,   307200, 0x50382370
+0,          3,          3,        1,   307200, 0x41a15136
+0,          4,          4,        1,   307200, 0xbc8c78ee
+0,          5,          5,        1,   307200, 0x19839e1b
+0,          6,          6,        1,   307200, 0x8545b93b
+0,          7,          7,        1,   307200, 0x4a4acf07
+0,          8,          8,        1,   307200, 0xefa1dee4
+0,          9,          9,        1,   307200, 0x22dae9ca
-- 
2.49.1


>From 73f67a23d292cf4018114dc820879d7e640d29c4 Mon Sep 17 00:00:00 2001
From: Niklas Haas <git@haasn.dev>
Date: Thu, 4 Dec 2025 13:10:47 +0100
Subject: [PATCH 2/2] avfilter/avfiltergraph: add missing newlines to format
 printing

---
 libavfilter/avfiltergraph.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/libavfilter/avfiltergraph.c b/libavfilter/avfiltergraph.c
index c15d95b91e..ad81d91bbc 100644
--- a/libavfilter/avfiltergraph.c
+++ b/libavfilter/avfiltergraph.c
@@ -485,13 +485,13 @@ static void print_filter_formats(void *log_ctx, int level, const AVFilterContext
     for (int i = 0; i < f->nb_inputs; i++) {
         const AVFilterLink *in = f->inputs[i];
         const AVFilterNegotiation *neg = ff_filter_get_negotiation(in);
-        av_log(log_ctx, level, "  in[%d] '%s':", i, f->input_pads[i].name);
+        av_log(log_ctx, level, "  in[%d] '%s':\n", i, f->input_pads[i].name);
 
         for (unsigned i = 0; i < neg->nb_mergers; i++) {
             const AVFilterFormatsMerger *m = &neg->mergers[i];
             m->print_list(&bp, FF_FIELD_AT(void *, m->offset, in->outcfg));
             if (av_bprint_is_complete(&bp))
-                av_log(log_ctx, level, "    %s: %s", m->name, bp.str);
+                av_log(log_ctx, level, "    %s: %s\n", m->name, bp.str);
             av_bprint_clear(&bp);
         }
     }
@@ -499,13 +499,13 @@ static void print_filter_formats(void *log_ctx, int level, const AVFilterContext
     for (int i = 0; i < f->nb_outputs; i++) {
         const AVFilterLink *out = f->outputs[i];
         const AVFilterNegotiation *neg = ff_filter_get_negotiation(out);
-        av_log(log_ctx, level, "  out[%d] '%s':", i, f->output_pads[i].name);
+        av_log(log_ctx, level, "  out[%d] '%s':\n", i, f->output_pads[i].name);
 
         for (unsigned i = 0; i < neg->nb_mergers; i++) {
             const AVFilterFormatsMerger *m = &neg->mergers[i];
             m->print_list(&bp, FF_FIELD_AT(void *, m->offset, out->incfg));
             if (av_bprint_is_complete(&bp))
-                av_log(log_ctx, level, "    %s: %s", m->name, bp.str);
+                av_log(log_ctx, level, "    %s: %s\n", m->name, bp.str);
             av_bprint_clear(&bp);
         }
     }
-- 
2.49.1

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