I am trying to encode a video to webm for playing through a HTML5 video tag. I have these settings...

ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:a 128k -b:v 1M -c:a libopus output.webm

The results aren't great, video has lost lot's of it's sharpness. Looking at the original file I can see the bitrate is 1694kb/s.

Are there any settings I can add or change to improve the output? Would maybe a 2 pass encode improve things?