[downloader/ffmpeg] Hide FFmpeg banner unless in verbose mode (#372)

Authored by: fstirlitz

yt_dlp/downloader/external.py

@@ -359,6 +359,8 @@ class FFmpegFD(ExternalFD):
             if self.params.get(log_level, False):
                 args += ['-loglevel', log_level]
                 break
+        if not self.params.get('verbose'):
+            args += ['-hide_banner']
 
         seekable = info_dict.get('_seekable')
         if seekable is not None: