The top part is more uniformed to make a video run smooth the bottom one looks like one of my animation
You don't make a "video" of your animated images (to import to SKS), just start with your 5 normal state images, then add each frame (of change/animation) after that, after you set the start loop image, and the end loop, save, and SKS does the rest.....Simple example, say I want the "start" text on start button to fade in and out, I first create the 5 normal states, then I add the frames for animation to that, in my example I will have a total of 11 images, first 5 normal states, next 6 will be my frames of animation, see example below:
now, I will need to set the animation frame starting point, which in this example will be frame 6, now set the animation frame stopping point, which will be frame 11, next you'll set the looping frame to start with, such as frame 6, then you'll end the loop on frame 11 (these settings you can play around with to get your desired results), next, you'll want to set the rate/speed at to which you want you animation to run at, and that can be done with the settings to the left of the frame settings, now save it, then SKS will do the rest. Granted, it's been a while (Win XP-Win 7) since I've done start button animations, so I may have left some steps out, but the example I've shown you I tested out on my machine (Win 10 OS). Hope this helps, this, as with all your future skins, will be by trial and error, and with any help from others, who will have the time to share their knowledge with you, good luck.