Now, I haven't really dealt much with video editing software, (audio is my specialty, so I am really video-program-retarted) but I am currently using Adobe Premiere Pro CS6 and whenever I bring in a clip that is great quality, trim a few scenes out, and export it; it gets super jaggy and well.. complete shit quality. I cannot figure out WHY or even what settings to mess with so that it just saves in the CURRENT quality that I originally imported.
I don't know what info might help you diagnose this, so go ahead and tell me exactly what (unless you already know). I really just wanted to make some simple 'cut out bad scenes, add fade in and out inbetween clips' shots. But get nothing but the worst quality imaginable.