Most modern day smartphones handles media output in the form of channels today. You have a channel that is responsible for the audio output of your ringtone, video playback, audio playback, notifications and sometimes in app notifications too. These channels are independent of each other and you can only play around with the channel settings when you activate the same.
There have been tweaks that are present in Android as well as with the latest update to Windows Phone 8.1 which allow you to change the volumes of these channels at the same time. However, for iPhone that is not the case. Not even after the announcement of the iOS 8 yesterday brought the ability to control these channels individually. However, thanks to the jailbreaking community you can do that. In case you have a jailbroken iPhone on iOS 7 then you can control the individual channels now.
This is done by a cydia tweak called Volume Mixer.The tweak is available for $0.99 from Big Boss Repo.The volume tweaks are added to the notification center when you install the tweak and the Control Center is left as it is.You can select to turn the Volume Mixer on or off in the Notification Center of the iPhone. You have the option of electing the volume controls that you wish to see in the Notification Center. The tweak gives you an option to theme the sliders as well as change the colors of the bars based on the position. The tweak is certainly wholesome and brings loads of personalisation options. Using the tweak, you can turn down the volume of the media playback without changing the notification tones.