I own a Xiaomi Redmi Note 5 with Android 8.1.0 installed and I recently found out that I cannot share videos of my dashcam on Whatsapp anymore.
Here's a link where I'll show the issue:
As you can see in the first video I shared (recorded on the 12th June 2018 and it's 190 MB video file), everything was fine.
The second one (recorded yesterday, the 4th August 2018 and it's a 120 MB video file), received the error message: "Can't send this video. Choose a different video and try again."
Both videos were recorded in the extreme mode but in the first one I had the 1.006 firmware installed, in the second one I had the 1.009 installed.
So I wonder, did recent firmwares change the video file format somehow?
By the way, before writing this post I had already contacted the Whatsapp support and they told me it could be a connectivity issue but as you could see from the video I linked, that's not the problem. I think it's the video itself.
I hope it can help you figure it out.
Have a great day.