[Voldemort]

Here is some tips with what to start

pawn Код:

new AudioOn[MAX_VEHICLES]; // On/Off also use OnPlayerEnterVehicle or at OnPlayerStateChange to sync
new AudioSource[MAX_VEHICLES]; // Audio source for stream, when someone enter car starts to play source
new AudioOnForPlayer[MAX_PLAYERS]; //To check if player hear music from car if yes on exit stop

you can make some 1 dialog where is all commands - start,stop,pause,volume etc

And use Audio_PlayStreamed(playerid,Stream,false,true,fals e);

If you want make really great its abit complicated, just remember you need to resync when ever someone change source in a car, so if there is others they also hear