If you want to play audio in a background you have to use a service.
If you’re using studio you can find out when an instance has stopped playing using EventInstance::getPlaybackState, or by adding a callback with EventInstance::setCallback and waiting for FMOD_STUDIO_EVENT_CALLBACK_STOPPED. If you’re using the lowlevel you can query Channel::isPlaying() or use a callback passed the Channel::setCallback and wait for FMOD_CHANNELCONTROL_CALLBACK_END.
Thanks for your reply. i understood second question’s reply. but in first quetion, i already knew that i have to use a service to play audio in a background. but when i play audio using activity, audio was also played in a background just like in the service. so i wondered how this can happen.