You can attach multiple images to an email but not videos.
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You are better of sharing one drive links to documents or folders if your collaborating on projects. Yes, it is moronic that the email hub defaults to the pictures when trying to add an attachment. Along with the fact that you can only attach one document to the email.. Drove me bonkers I can tell you.
The OneDrive method imo is much better as not only you and your colleague can use webapps. But also don't have the problem with multiple versions of an attachment floating around.
Edit: Updated post with images.
Also this is the solution I used, I created folder in my work's one drive email, shared the folder with my account that is tied to my phone along with a folder shortcut (copied the link with edit permissions) so I can store it on my pc at work and at home. Voila I could edit work documents on my phone, at work and at home - completely in sync. Same worked for collab folders with colleagues.