FFmpeg is the media converter. If you don't want to use a command line to access it, use the FFE frontend if you're on Windows.
FFE uses your existing installation of FFmpeg (which must be added to your PATH) and executes the command line instructions for you. It's not as powerful for doing very advanced things, but it allows you to do almost anything a normal file conversion would require.
I use it with the Open With dialogue in the context menu for my media files to quickly open that file. Then I just change the file extension in the second field, Output, and hit Do It! to convert the file.
The nice thing about this solution is that it's entirely free, FFmpeg is very powerful, and FFE is a great way to use the freedom and power of FFmpeg without having to memorize and type out long command line inputs.