So your friend popped the question at a concert last week, and your only evidence is a pixellated, under-lit cell phone video? Free webapp FixMyMovie won't get you up to HD-quality, but it can cure many of digital video's common ailments. Upload a video (original files are best), compare the "before" and "after" segments, then give FixMyVideo the job and preview your smoothed-over video in full screen, with the option to grab still screenshots at any point. I didn't have a video file of the tossed-off kind FixMyMovie can best help, but the MakeUseOf.com folks seem to vouch for this free service.
FixMyMovie [via MakeUseOf.com]