The Galaxy S8 and S8+ will be capable of shooting and playing 4K video at 120 frames per second via an external monitor. But make sure that the 4K video should be included in Galaxy S8 playable 4K file formats such as 4K MP4, 4K AVI, 4K WMV, 4K MKV, you will fail to open some 4K files such as 4K MXF, 4K Prores, 4K XAVC/XAVC S on Galaxy S8.
Samsung Galaxy S8 vs Samsung Galaxy S7 Edge
Both the phones have their pros and cons,lets analyze both:-
Advantages of Samsung Galaxy S8
1.Faster CPU:- Faster CPU means more smooth experience.
2.Bigger Screen:-Reading, browsing internet and watching movies is more pleasing experience on a bigger screen.
3.Better Screen Resolution:-More resolution means sharper and crisper screen.
4.More Storage Capacity:-More memory allows you to store more songs, videos, photos and install more applications.
Advantages of Galaxy S7 Edge:-
1.Bigger Battery:-With more battery size, device's battery can generally last more time.
Verdict - In my opinion, Samsung Galaxy S8 is better overall performance and price ,if you need bigger battery you can go for Galaxy S7 Edge .
You can also compare these devices on 91mobiles
Out of these, Samsung Galaxy S8 has much better display quality, better performance, has wide-angle selfie camera and it also has fast charging support.
To see the full comparison: Samsung Galaxy S8 vs Samsung Galaxy A7 2018
I would any day recommend you go for the Oppo F9 Pro. Not only it is much cheaper, but also offers better features:
1. Screen: 6.3 inches (Oppo F9 Pro) vs 5.8 inches (Samsung Galaxy S8)
2. RAM: 6 GB (Oppo F9 Pro) vs 4 GB (Samsung Galaxy S8)
3. Front camera: 25MP (Oppo F9 Pro) vs 8MP (Samsung Galaxy S8)
4. Primary Camera: 12MP (Oppo F9 Pro) vs 16MP + 2MP (Samsung Galaxy S8)
5. Battery: 3500mAh (Oppo F9 Pro) vs 3000mAh (Samsung Galaxy S8)
Comparison: Samsung Galaxy S8 vs Oppo F9 Pro
It depends upon your requirements, On one side Samsung Galaxy S8 has an excellent display with better camera quality, while on the other side, Samsung Galaxy A9 has triple cameras, with longer battery life.
To see the complete comparison : Samsung Galaxy S8 vs Samsung Galaxy A9