Telegram is working on video stickers
An API Schema update revealed a mention on video stickers.
Likely, users will be able to create stickers from regular raster videos. We can assume a video format with transparency support will be used. One of the most popular such formats is WebM.
Currently all animated stickers are vector. To create your own animated stickers for Telegram, you need Adobe After Effects skills. Video stickers will make animated stickers easier to create, will allow to use camera footage or, for example, 3D animation.