Why can't I upload my DSLR Photos on instagram?

I take alot of videos with this camera and people have been asking me for videos of their cars since january. I have incredible footage of things snd taken with my Nikon D3100 however when I trto upload the video to Instagram it tells me the file is unsupported. Why is this and how can I work my way around by still using my camera I have a Galaxy S3 so I can't use any iphone stuff.
My instagram is @coles_cars

I think it's most likely because the file is too big for Instagram to process as my DSLR photos used to crash my app and sometimes whole phone. Either that or you're shooting in RAW format? Downsize the files first and then it should work fine.

-Just realised it is video, sorry I never noticed… Convert your video into another format or use an editor and export as MP4 or something.

Try this:

http://www.premiumbeat.com/blog/how-to-edit-and-encode-videos-for-instagram/

The file [the video format] is unsupported.

It's clear enough surely?

Find out what format instagram supports, and convert the video to a supported file format using your video editing software.

Instagram is meant for smartphones and tablets only. A workaround is to run Android in your computer.