Controlled by CIV4EraInfos.xml tags :
<iSoundtrackSpace>
<bFirstSoundtrackFirst>
<EraInfoSoundtracks>
<CitySoundscapes>
You can do this one of two ways.
1. You have the foldiers in your mod, or foldier, and have the xml that deal with audio music have references for each song
2. Use the "custom soundtrack" option in the options menu, click it, then browse and find the foldier where your music is located, the game will then play the songs in that foldier.
<SoundData>
<SoundID>SONG_ANCIENT_SOUNDTRACK_1</SoundID>
<Filename>Sounds/Soundtrack/Classical/AncientSoundtrack1</Filename>
<LoadType>STREAMED</LoadType>
<bIsCompressed>1</bIsCompressed>
<bInGeneric>1</bInGeneric>
</SoundData>
<Script2DSound>
<ScriptID>AS2D_ANCIENT_SOUNDTRACK_1</ScriptID>
<SoundID>SONG_ANCIENT_SOUNDTRACK_1</SoundID>
<SoundType>GAME_MUSIC</SoundType>
<iMinVolume>70</iMinVolume>
<iMaxVolume>70</iMaxVolume>
<iPitchChangeDown>0</iPitchChangeDown>
<iPitchChangeUp>0</iPitchChangeUp>
<iMinLeftPan>-1</iMinLeftPan>
<iMaxLeftPan>-1</iMaxLeftPan>
<iMinRightPan>-1</iMinRightPan>
<iMaxRightPan>-1</iMaxRightPan>
<bLooping>0</bLooping>
<iMinTimeDelay>0</iMinTimeDelay>
<iMaxTimeDelay>0</iMaxTimeDelay>
<bTaperForSoundtracks>0</bTaperForSoundtracks>
<iLengthOfSound>0</iLengthOfSound>
<fMinDryLevel>1.0</fMinDryLevel>
<fMaxDryLevel>1.0</fMaxDryLevel>
<fMinWetLevel>0.0</fMinWetLevel>
<fMaxWetLevel>0.0</fMaxWetLevel>
<iNotPlayPercent>0</iNotPlayPercent>
</Script2DSound>
<iSoundtrackSpace>0</iSoundtrackSpace>
<bFirstSoundtrackFirst>0</bFirstSoundtrackFirst>
<EraInfoSoundtracks>
<EraInfoSoundtrack>AS2D_ANCIENT_SOUNDTRACK_1</EraInfoSoundtrack>
<EraInfoSoundtrack>AS2D_ANCIENT_SOUNDTRACK_2</EraInfoSoundtrack>
<EraInfoSoundtrack>AS2D_ANCIENT_SOUNDTRACK_3</EraInfoSoundtrack>
<EraInfoSoundtrack>AS2D_ANCIENT_SOUNDTRACK_4</EraInfoSoundtrack>
</EraInfoSoundtracks>
Padjur hit it.
The game will not play anything unless its a mp3.
If you are trying to mess with this in C2C, don't. It has some Python that does things for sound. If you just want to add tracks for an era all you need to do is put them in the Sounds/Soundtrack/EraNew folder where "EraNew" is the one for the era the music file goes with like AncientNew or ClassicalNew. When you start the game up it should automatically edit the XML for you and move the mp3 file into the non-New folder. This is done by the MusicUpdate.py file in the Python/AIAndy folder, if you were wondering.