How would I change the file extension of multiple files at the same time?

Are you trying to change the format, or simply change the name?

@papayalily
The format is flash, but for some reason a few of my files end in the extension mp4, so I want to change that so when I open them they don’t open in my quicktime player.

@takaboom Download Ken Rename, and you can mass rename them in that.

You can try métamorphose an open source file renamer.
The best i have found so far

For windows you can get a command prompt by going to Start->Accessories->Command Prompt (I’m using XP, so this might be slightly different for yours)

This will basically drop you in to DOS (which is basically the pre-windows operating system), you’ll just need a few commands to pull off what you want.

Short answer:

Figure out what folder the files you want to rename are in and type

cd <full folder structure>

So for example

cd C:\Documents and Settings\funkdaddy\Desktop\flashfiles\

then rename them all at once with

ren *.mp4 *.flv

and you’re done

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Longer answer with explanation and references:

You can navigate to the folder you want to work with by typing “cd <folder name>” (a 20 second intro to cd) you can see a list of files by typing “dir” (intro)

Once you’re in the folder where your files are located then you’ll just need to rename the files with “rename <old name> <new name>” (intro to rename) ren or rename work the same.

You can use an asterisk (*) as a wildcard, so to rename them all at once you’d use

ren *.mp4 *.flv

And you’re done.

If you’re on a Mac, Automator should have something like that.