Run Trainspotter and click “Edit”->”Preferences”

Click the “Get lame here” link, a browser opens. Note that as it says on the site “… visitors should be aware that download and usage of some binaries (namely, MP3 encoders and AAC encoders/decoders) may be forbidden due to patent legislation in their Countries. Consult your Country's software patent laws for more details.” If you’re not going to be breaking any laws in your country, click the “download” link as shown below:

Scroll down to the Lame 3.98 for MacOS X and click the “download” link

Click OK

You should see a window as above. Next open Finder and navigate to “Applications/Utilities” and next drag and drop the “lame” file in the window above in to the “Utilities” directory

Above is what Finder should look like afterwards.

Now go back to the Trainspotter Preferences

Now you can either click the “Browse” button, next to the “Path to LAME MP3 encoder” and select the lame executable, or type /Applications/Utilities/lame

Now we do a similar thing for FLAC, first click the “Get FLAC here” link on the preference page

In the browser click “Flac tools for OS X”

Now click flac-1.2.1-darwin-ppc+i386

Click flac-1.2.1.dmg

Click OK

You’ll then find the flac disk image mounted in Finder.

Double click the flac-1.2.1.mpkg

Install flac, accepting all the defaults

Go back to the Trainspotter preferences page

For the “Path to FLAC encoder” enter /usr/local/bin/flac, as above.

Scroll down in the preferences window and click “Apply” and then “OK”

Click Tools->Detect Keys…

You’re ready to start key detection.