Problems creating new output formats

I would like to download videos without any audio Keeping everything else original. Actually I'm not even fussy about the original format, I just want the audio gone. So I go to 'Output Formats' -> 'Add new format'. I select ''Computer' as the target device and 'No Audio' for the audio codec but when I save I get the error "Invalid Conversion Parameters Specified". So I figure it doesn't like that I've left the other fields blank so I fill them out but even then it still says their invalid. I tried many combos of options but no matter what I select I always get the same error. So: 

1) Can you tell me what I can put in here that will be accepted?

2) (Just a suggestion) Maybe tell the user why it's invalid.

Running v4.3.2124.0

Thanks