I record little screencasts/demos regularly for embedding them on webpages and currently always convert them with the ffmpeg CLI to WEBM, but it's really cumbersome and hard to remember all the command line flags you need to use (especially with 2 passes). I don't really like online cloud converters though because each video needs to both be uploaded and downloaded again and I'm worried they do a lossy compression on the video behind the scenes. A simple to use, trustworthy, client-based webapp to do this would be amazing.
And end up with really good results out the other end. When I was rendering with pre-VP9 I needed a few more flags (stuff like crf) to maintain quality, but this works fine for most things. And has been really impressive on the filesize side of things.
