[downloader/ffmpeg] Accept output args from info dict
diff --git a/yt_dlp/downloader/external.py b/yt_dlp/downloader/external.py
index ce5eeb0a9a2..8b0b94e7256 100644
--- a/yt_dlp/downloader/external.py
+++ b/yt_dlp/downloader/external.py
@@ -491,7 +491,7 @@ def _call_downloader(self, tmpfilename, info_dict):
         if not self.params.get('verbose'):
             args += ['-hide_banner']
 
-        args += traverse_obj(info_dict, ('downloader_options', 'ffmpeg_args'), default=[])
+        args += traverse_obj(info_dict, ('downloader_options', 'ffmpeg_args', ...))
 
         # These exists only for compatibility. Extractors should use
         # info_dict['downloader_options']['ffmpeg_args'] instead
@@ -615,6 +615,8 @@ def _call_downloader(self, tmpfilename, info_dict):
         else:
             args += ['-f', EXT_TO_OUT_FORMATS.get(ext, ext)]
 
+        args += traverse_obj(info_dict, ('downloader_options', 'ffmpeg_args_out', ...))
+
         args += self._configuration_args(('_o1', '_o', ''))
 
         args = [encodeArgument(opt) for opt in args]
diff --git a/yt_dlp/extractor/common.py b/yt_dlp/extractor/common.py
index e776ccae924..a36a6187c58 100644
--- a/yt_dlp/extractor/common.py
+++ b/yt_dlp/extractor/common.py
@@ -246,7 +246,8 @@ class InfoExtractor:
                     * downloader_options  A dictionary of downloader options
                                  (For internal use only)
                                  * http_chunk_size Chunk size for HTTP downloads
-                                 * ffmpeg_args     Extra arguments for ffmpeg downloader
+                                 * ffmpeg_args     Extra arguments for ffmpeg downloader (input)
+                                 * ffmpeg_args_out Extra arguments for ffmpeg downloader (output)
                     * is_dash_periods  Whether the format is a result of merging
                                  multiple DASH periods.
                     RTMP formats can also have the additional fields: page_url,

Needed for #9158


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