Why turn a GIF into a video?
GIF is a format from 1987. It stores every frame as a separate picture with at most 256 colors and only simple compression, so a few seconds of animation easily become several megabytes. A video codec such as H.264 or VP9 only stores what changes from one frame to the next and handles color far better. GIFs made from video clips or photos therefore usually shrink to a fraction of their size, while small GIFs with a few flat colors, such as icons, gain little and can even get slightly larger.
That matters wherever size counts: web pages load faster, chat apps and social networks accept the file without complaining about size limits, and slides or emails stay light. Many sites already show GIFs as video behind the scenes for exactly this reason.
What happens to timing, transparency and odd sizes
Each frame of the GIF goes into the video with its own duration, so slow and fast parts of the animation play exactly as before. Frames that a GIF marks with no delay play at 0.1 seconds, which is what browsers do as well.
MP4 and WebM videos made here have no transparency, so transparent parts of the GIF are filled with the background color you choose. White is the default. H.264 also needs even width and height; if your GIF is 375 pixels wide, the video gets one extra column that repeats the edge pixels, so nothing is stretched or cut off. Very small GIFs, under 32 pixels on a side, are enlarged by a whole factor because video encoders do not accept such tiny sizes; the pixels stay sharp.
A video plays once unless the player loops it. Websites and most social networks loop short videos automatically, but if you want a longer clip, for example for a presentation, set Repeat to 3, 5 or 10 times.