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How to Convert Fullscreen Videos to Widescreen (or vice versa) with no Loss in Quality. Download MKV Merge (best to Google as you will get latest version and as we all know Youtube links cannot be trusted) I used to Encode all my Fullscreen HD videos to Widescreen which was a big mistake. It took time (2 converters) and slight quality loss. Untill i discovered MKV Merge can do it. I had HD Videos of The Simpsons and The Next Generation that were all in their Original Resolution and that bothered me even though i can load them up in my Video Players exactly how i wish. I couldnt use them as an example else id be in trouble with Youtube for copyrite, so i use a Computer Game Clip instead. Load your Video into MKV Merge, select your Resolution, Mux it, Done. The First Mux i selected 16:9 which stretches the Video to fill the screen (No More left and right Black Boxes) The Second Mux was 2.35 Option which gives top and bottom black bars, if you wish to see your Videos that way. (My Prefered Option)