So open up your video into iMovie
You will find the little nut/bolt/tool thingy and when you click it, it will lead you into this tab. Click ‘clip adjustments’
When it is opened you will find this window. You can adjust the speed and the direction it is playing. You may also leave it as it is.
This window will open. Make sure to choose ‘Movie to Image Sequence’ in the export options. Once you have done that, click onto options.
This smaller window will open. Make sure the format is jpeg. For the ‘frames per second’ the higher number (such as an 8) will give you a much smoother gif. This is preferable if your clip is 1.5 seconds long or under. Longer than that, you will opt to choose a smaller number. This is to reduce the file size to under 500kb to upload onto tumblr. Once everything is good, just click ‘okay’ and then save.
When this window pops up, make sure to fill in the space with the same number as you did in ‘frames per second’ in iMovie. After clicking ‘OK’ edit to what you please. However darker colours will build up the file size (idk manz, don’t ask me why)
This large window will pop up. Change the gif size to 500 so it is uploadable on tumblr. Altering the number for ‘Colours’ will not make much of a difference. The higher the number the higher the quality. ‘Dither’ controls the amount of detail put into the gif. The higher the number the higher detail. Altering this number may cause a slight change in file size. As for ‘Lossy’, when changing the number you will notice the amount of grain in the gif. Even if there is a small increase in ‘Lossy’ there will be a dramatic decrease in file size. You don’t want too much lossy or too little dither. Make sure it is under 498kb. Make sure the looping options are on ‘Forever’.
After that. Click save! You may now enjoy your gif.