This may help
Vivaldi via update to version 1.6.689.46-1 Changelog since the second 1.6 release [Linux] Vivaldi does play proprietary HTML5 video and audio on Ubuntu with chromium-codecs-ffmpeg-extra 55.0.2883.87 (VB-24384)
This may help
Vivaldi via update to version 1.6.689.46-1 codecs- ffmpeg- extra 55.0.2883.87 (VB-24384)
Changelog since the second 1.6 release
[Linux] Vivaldi does play proprietary HTML5 video and audio on Ubuntu with chromium-