[FFmpeg-devel] [PR] avfilter/dnn: add synchronous execution path in torch backend (PR #21654)

[Steven Xiao via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>]

PR #21654 opened by Steven Xiao (younengxiao)
URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21654
Patch URL: https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/21654.patch

When using `dnn_processing` filter with torch backend, FFmpeg hangs indefinitely because no inference is actually performed.
Resolve this problem by add "else" branch for synchronous execution path.

Usage:
    ffmpeg -i input.mp4 -vf scale=224:224,format=rgb24,dnn_processing=dnn_backend=torch:model=sr_model_torch.pt:device=cpu output.mp4


>From 5b5324d6242eee72cba10365ac9c36ad69481d78 Mon Sep 17 00:00:00 2001
From: stevxiao <steven.xiao@amd.com>
Date: Thu, 5 Feb 2026 11:34:07 -0500
Subject: [PATCH] avfilter/dnn: add synchronous execution path in torch backend

When using `dnn_processing` filter with torch backend, FFmpeg hangs indefinitely because no inference is actually performed.
Resolve this problem by add "else" branch for synchronous execution path.

Usage:
    ffmpeg -i input.mp4 -vf scale=224:224,format=rgb24,dnn_processing=dnn_backend=torch:model=sr_model_torch.pt:device=cpu output.mp4
---
 libavfilter/dnn/dnn_backend_torch.cpp | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/libavfilter/dnn/dnn_backend_torch.cpp b/libavfilter/dnn/dnn_backend_torch.cpp
index 33809bf983..56fbe372d1 100644
--- a/libavfilter/dnn/dnn_backend_torch.cpp
+++ b/libavfilter/dnn/dnn_backend_torch.cpp
@@ -424,6 +424,14 @@ static int execute_model_th(THRequestItem *request, Queue *lltask_queue)
         }
         th_model->cond->notify_one();
         return 0;
+    } else {
+        // Synchronous execution path
+        ret = th_start_inference((void *)(request));
+        if (ret != 0) {
+            goto err;
+        }
+        infer_completion_callback(request);
+        return (task->inference_done == task->inference_todo) ? 0 : DNN_GENERIC_ERROR;
     }
 
 err:
-- 
2.52.0

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