How Rescaled to project size (FFMPEG only) works

• When Rescaled to project size (FFMPEG only) is checked, the size of the video data to be computed will always be the same as the Project Format. The size of your video is scaled down to the Scale factor BUT then it is rescaled up to the Project Format. For example, your Project Format is 1920x1080 and Proxy's Scale factor is ${\frac{{1}}{{4}}}$, then your videos (1920x1080) will be scaled down to 480x270 and then up-scaled to 1920x1080. All the Effects/Plugins work correctly because the original resolution/geometry/size is not changed. For an old computer, this option is not recommended.
• When Rescaled to project size (FFMPEG only) is UNchecked, the size of the video data to be computed will be reduced to the Scale factor. The size of your video is scaled down to the Scale factor. For example, your Project Format is 1920x1080 and Proxy's Scale factor is ${\frac{{1}}{{4}}}$, then your videos (1920x1080) will be scaled down to 480x270. It works as if the Project Format were 480x270 (and really it works). If you take a look at Settings → Format... when Proxy is enabled (Active), you can see that the Width and Height are changed according to the Scale factor; you absolutely must NOT change these values! The good thing is that your computer will be faster. The bad thing is that some Effects/Plugins do not work as expected because they use pixel units. Examples are Title and Blur plugins. A workaround is needed for that.

Note: the dimensions of the frame/image are downscaled to the Scale factor; so if the Scale factor is ${\frac{{1}}{{4}}}$ and the dimension of the image is 4288x2848 pixels, that image will be downscaled to 1072x712. It doesn't matter what the Project Format is.