Scaling background images without background-attachment: fixed? - html

Question

I'm trying to figure out the best method for making a background image fully responsive - so far the best way I can figure out is to use background-size: cover, as most people tend to suggest, but with background-attachment: fixed so that the image scales down it's proportions as the screen resizes, otherwise it just retains it's original proportions and doesn't scale at all. Using just background-size: cover stretches the image to fill the container div, but won't automatically scale proportions..
However I don't want the effect of fixed background that hides part of the image as you scroll down and would prefer it to be background-attachment: scroll, but I can't get that to work and make it scale as well.
So my question is: is there any way I'm not aware of to have the background images scale automatically with screen size without having to use background-attachment: fixed to achieve it?
Please see my JSFiddle for what I've got at the moment: https://jsfiddle.net/uhoL5d5w/2/
(and yes I'm also aware I will be needing to use media-queries at some point to serve optimized images to the various screen sizes)
My current code looks like:
<header>
<div class="launch-bg">
<nav class="menu">
</nav>
</div>
</header>
<div class="page-wrapper">
</div>
<div class="push"></div>
<!-- Footer -->
<div class="footer"></div>
html,
body {
#include box-sizing(border-box);
height: 100%;
}
div,
body {
margin: 0;
padding: 0;
}
body {
display: block;
background-color: #000000;
}
.page-wrapper {
margin: 0 auto -900;
min-height: 100%;
height: auto;
}
* {
margin: 0;
padding: 0;
}
header {
display: block;
width: 100%;
height: 1200px;
}
.launch-bg {
height: 1200px;
background-image: url('http://s8.postimg.org/56xlj2rc5/launch_bg.jpg');
background-repeat: no-repeat;
background-attachment: fixed;
background-position: center center;
background-size: cover;
}
.footer {
height: 900px;
padding: 6% 0;
color: $white;
background-image: url('http://s8.postimg.org/onib5lmg5/footer_bg.jpg');
background-repeat: no-repeat;
background-attachment: fixed;
background-position: center center;
background-size: cover;
}

Answer 1

Here's a simple example, I think, of what you're asking for, just trimmed it all down for clarity:
header {
display: block;
width: 100%;
height: 1200px;
background-image: url('http://s8.postimg.org/56xlj2rc5/launch_bg.jpg');
background-repeat: no-repeat;
background-attachment: scroll;
background-position: center center;
background-size: cover;
}