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"User-Agent" is only edited on the "playlist" editor page, but I can not add the playlist which require the "User-Agent" when it gets the error result when fetching the playlist.

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1. If it is possible, adding a new field for the "User-Agent" when adding the playlist url;
2. Still saving the playlist record, even though fetching playlist url error, then we could update the playlist and refrech.

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