Actually you bring up a good point: When I export a project as mp3 it asks me for that extension hit or miss - not every time. I mostly do not have to specify “.mp3” as I have mp3 selected in the Type drop-down.
Please read this Frequently Asked Question for an explanation of this behaviour:
Audacity Manual .
I never have a “.” in my mp3(or wav) filenames.
I sometimes do have a filename like: “Money For Nothing(Remastered)” or “Money For Nothing - Remastered”
Could either of those trigger a request for extension?
Hyphens, underscore, space, upper and lower case letters (a-z A-Z) and numbers (0 to 9) should all be “safe” characters in file names. The rules about other characters can be quite complicated on Windows (see here: http://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx )
I would generally advise sticking with “safe” characters.
If you mean, does it trigger a warning “You are about to save an MP3 file with the name…” then the answer should be no. Only a dot triggers that warning.
But as that FAQ says, these characters are illegal in file and folder names on Windows:
/ : * ? " < > |
so will probably produce some other type of warning.
If the files are just for your own computer and your own use then you can use any printable characters other than those nine invalid ones. Windows Media Player will be quite happy playing a file called ▼◊.wav if it is a recent version of WIndows.
If you want to use the exported file on another computer or send it to someone else you should stick to A to Z characters, numbers and underscores ( _ ). Even spaces can be a problem if you want to send the file over the internet.
Large numbers of characters in file paths (the file name and the folder structure the file is in) and “reserved device names” like “COM1” adds to the complication as per Steve’s link, but most users won’t fall file of those.
Ok. So the file type extension warnings I randomly get remain a mystery. Probably a Vista mystery. But thanks for tabling all of the known reasons for the warnings.
As ever, it’s impossible to comment without specifics - exactly what the message says (attaching an image is good) and exactly what steps you take prior to the message appearing.