ffmpeg - Convert MP4 to WebM, poor results

Question

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?

Solution

Try with

ffmpeg -i input.mp4 -c:v libvpx-vp9 -crf 30 -b:v 0 -b:a 128k -c:a libopus output.webm

Adjust the CRF value till the quality/size tradeoff is ok. Lower values produce bigger but better files.