I think that happend because when you reduce the width of the video the height still the same as before and the border radius does’t affect. See the following image:
Do you see in the image how the radius of the edge looks a little cut when I leave the video with a higher height?
I think one solution could be, besides change the width to 200px, also change the height to same or similar as you can see in the following image.
Try it and let me know if this helps 🙂