Compression. Because that's what you are comparing it to...other people's "sites." So you are comparing it to how it looks, compressed, on the web. Well, it's also color correction. If you want good looking images, it isn't all lenses and camera, color correction plays a BIG role. Quality of blacks...that's part of color correction. Get a professional colorist to work on your footage.
And then compression. That is a dark art. Because compression always means tossing out some, or a lot, of color information. how else are you going to make the image smaller? Unless you throw out some picture quality...that's what makes the files so big. So, you need to work on all sorts of compressing types. Test what looks good...or hire someone to do this for you.
Shane
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