The resolution of the video is more then enough (see last image)
And yes this render is low on samples… but it’s the same on higher samples.
I have tried changing the blend mode of the material but nothing changes
It’s that glow on your video. And if your video is MPEG-4/H.264, that codec compression will also contribute for a low resolution in your scene. Best thing to do is render again your video without glow, and apply in the compositor.