Adding to "Open with" list [OSX 10.9.2]

My Mac doesn't think Audacity can open mp4 files, so when I want to do so using "Open with", I have to switch from "Recommended Applications" to "All Applications" so as to select Audacity.

This is only for when I want to extract the audio; I do not want to make Audacity the default app. I am fine with Quicktime being the default.  

The question is, can I identify Audacity as being capable of opening an mp4 so I don't always have to switch to "All applications"?
You need to edit Audacity's Info.plist file and add mp4 to the list of files it handles.

Using a text editor, open /Applications/Audacity.app/Contents/Info.plist (this is assuming Audacity is installed as Audacity.app, it might be slightly different).

Then, find the section for CFBundleDocumentTypes which should list the supported types like:

&lt;key&gt;CFBundleTypeExtensions&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;...&lt;/string&gt;
        &lt;string&gt;...&lt;/string&gt;
        &lt;string&gt;...&lt;/string&gt;
    &lt;/array&gt;

Then just add a new line for mp4: &lt;string&gt;mp4&lt;/string&gt; and save the file.

To get the LaunchService to pick up your change, you have to run (in Terminal):

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user

After that, Audacity should show as a Recommended Application for mp4 files.