[Threshold]

Example:

pawn Код:

public OnPlayerStateChange(playerid, newstate, oldstate)
{
    if(newstate == PLAYER_STATE_DRIVER)
    {
        if(oldstate == PLAYER_STATE_ONFOOT)
        {
            for(new i = 0; i < MAX_PLAYERS; i++) //foreach is an alternatively better method
            {
                if(IsPlayerConnected(i))
                {
                    if(IsPlayerInVehicle(i, GetPlayerVehicleID(playerid)))
                    {
                         PlayRadioStationForPlayer(i);
                    }
                }
            }
        }
    }
    if(newstate == PLAYER_STATE_ONFOOT && (oldstate == PLAYER_STATE_DRIVER || oldstate == PLAYER_STATE_PASSENGER))
    {
           StopAudioStreamForPlayer(playerid);
    }
    return 1;
}

Only thing that concerns me is that the radio may not stop for everyone in the car when the driver exits the vehicle.