[FfmpegMetadata] Write id3v1 tags

yt_dlp/postprocessor/ffmpeg.py

@@ -769,6 +769,9 @@ class FFmpegMetadataPP(FFmpegPostProcessor):
             if value is not None and mobj:
                 metadata[mobj.group('i') or 'common'][mobj.group('key')] = value
 
+        # Write id3v1 metadata also since Windows Explorer can't handle id3v2 tags
+        yield ('-write_id3v1', '1')
+
         for name, value in metadata['common'].items():
             yield ('-metadata', f'{name}={value}')