diff --git a/yt_dlp/postprocessor/ffmpeg.py b/yt_dlp/postprocessor/ffmpeg.py
index 0c8d4611d..d0a917379 100644
--- a/yt_dlp/postprocessor/ffmpeg.py
+++ b/yt_dlp/postprocessor/ffmpeg.py
@@ -347,6 +347,7 @@ class FFmpegPostProcessor(PostProcessor):
         _, stderr, returncode = Popen.run(
             cmd, text=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
         if returncode not in variadic(expected_retcodes):
+            self.write_debug(stderr)
             raise FFmpegPostProcessorError(stderr.strip().splitlines()[-1])
         for out_path, _ in output_path_opts:
             if out_path: