not sure if its the same with android, but i have an iphone and this is how i did it.

requirements: video must be a minute or shorter. can choose to have the sound on or off for the clip.

1. upload video to imgur. make sure to keep it "hidden" if smoking/naked this does not affect the ability to share it to reddit. this just prevents imgur from removing it and flagging you. (spoken from experience)

2. go to the video and LONG PRESS ON the video until it gives share options. if you hit the share button it offers in the corner it will not provide the correct link. you want whatever gives you a link with ".mp4" at the end. this step is crucial.

3. paste the link into your notes or right into reddit & change the link's ".mp4" to ".gifv" which is also a very crucial step.

4. post the link to reddit as a link, then send post as usual. and as long as the previous steps are followed there shouldn't be any issues of it converting itself to a video once published.

ALTERNATIVELY, you can turn the video into a gif and upload as a photo. although, i don't recommend this method as it has to be low quality and much much shorter. 7-30s (depending on what platform it's made on.) also will not have sound if made a gif. some platforms to do this include giphy, gif maker, tumblr

ALTERNATIVE #2 use redgifs! i just learned this works. pretty much the same method as imgur except much easier for you don't have to change the .mp4 or anything. just copy the link and paste it as a link and boom!