Large files like more than 16MB could not be
shared on WhatsApp by default...
This feature is only needed for videos
sharers.
When it comes to images and audio message
it may not take that much size to share.
But video it takes alot for size.
Inorder to send video’s of size more than
16MB, you need to compress the size of video.
Among best video converter apps available
in play store, using VIdeo Converter Android
gave good results and I do recommend to use
it for compressing your video..
Download => Video Converter Android App