It is vital for players to understand that export keys are no longer functional for the vast majority of titles. The ability to export songs relied on music licensing agreements between the game publisher (Harmonix/MTV Games/EA) and the copyright holders of the songs.
Music licenses are temporary. When these contracts expired, the publishers were legally required to remove the songs from the digital storefronts and disable the export servers.
When exporting from Rock Band games, some stems are muted during sections where an instrument drops out. You must ensure you export the entire song or manually paste the section where the guitar plays a full chord.
Here is the current status of export keys for major titles:
Rock bassists typically play root notes on beats 1 and 3. Import the bass stem into a tuner plugin (e.g., GTune by GVST). Play the first 4 bars. The most dominant pitch is your key.
Example: If the bass plays primarily C, F, and G, your key is C major. Example: If the bass plays A, D, and E, your key is A minor (relative minor of C).