How can I lower the media volume on my iPhone when no media is playing? On the laptop it's a one-touch mute button, nice and easy.

On my iPhone there is no mute button, so volume controls must be used instead, which is no problem. When I use the volume buttons when there are no media playing, it lowers my ringer volume.

The issue is that I have to wait at least until the video player loads, and depending on which video player I am using, the both volume slider is grayed out out until the video starts playing.

The combination leads to a nonzero period of time when I am exposed to the audio while I am lowering the volume.

Q: Is there a way to adjust the media volume when there is no media playing [yet]?
The control center works (swipe up from bottom of screen and slide volume slider as desired).

In iOS 9 at least, you can also go Settings -> Sounds and under the Ringer and Alerts section, turn off "Change with Buttons", then use the volume buttons on the side of the phone to adjust the media volume. You can leave this option off to always have media volume control with the hardware buttons if you are OK with the ringer volume being just off or on at a preset level using the silent toggle switch on the side of the phone.