Now use the left and right arrow buttons to find a new resolution that matches your desired resolution. Note that with standard resolutions, such as 480p/576p/720p/1080p, for widescreen films (16:9 or greater) you want a resolution that is 854/1024/1280/1920 pixels wide respectively, but for fullscreen films (less than 16:9), you want a resolution that is 480/576/720/1080 pixels high respectively. Once you have found a good resolution, press Apply.
If your video is not progressive, you cannot use this option. This allows you to crop and/or resize your source video without the need for using an AviSynth script. Do not use this parameter in your test encodes, only for the full encode. When you perform the full encode, copy the crop and resize numbers to x264. Remember to crop before resizing. The syntax is as follows: