You can record up to 1080p resolution videos on Vivo Y81i. You cannot record 4K videos via Vivo Y81i.
Vivo Y81i is made of Aluminum Alloy and industrial grade polycarbonate material.
Vivo Y81i comes with 5V / 1A charger. It does not support the fast charging.
Vivo Y81i has 2GB RAM of LPDDR3 type.
Yes, Vivo Y81i does have a dedicated MicroSD card slot.