Symbols are replaced with underlines

[ghost]

• I've verified and I assure that I'm running youtube-dl 2017.07.30.1
• At least skimmed through the README, most notably the FAQ and BUGS sections
• Searched the bugtracker for similar issues including closed ones

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• Other

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I've noticed that every symbol ( e.g. (xyz) -> xyz ) are replaced but i don't using the option --restricted-filename. Thats my command that I use:

youtube-dl -o '/var/www/ytdl/downloads/%(title)s.%(ext)s' --format 'bestaudio[ext=m4a]' --default-search 'ytsearch' --prefer-ffmpeg -x --embed-thumbnail --metadata-from-title '%(artist)s - %(title)s' --add-metadata --audio-format m4a --audio-quality 0 "link"

So why does youtube-dl replace these characters?

[dstftw]

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