My camera records videos in a Sony version of AVHD, producing some large files, but I usually edit them using Movie Maker, so end up saving them as either .WMV or MP4. Here's the stats: Original file from camera 750MB Import to Movie Maker and virtually no edit to overall length, just fade in/fade out... Saved as MP4 = 150MB Saved as WMV = 300MB Google seems to think that MP4 files are larger than WMV files for the same item - my file sizes say the reverse . But more importantly, is there any playback quality benefit to audio or visual in saving and then uploading (to YT and/or FB) the larger WMV over the smaller MP4 - I understand YT compresses them to it's own format anyway, though I don't know about Facebook I'm not bothered about upload time as I tend to leave them overnight. Ta .