Why does fladder always transcode when it doesn't need to?

[Matthematic]

I'm noticing that for the same exact file, when jellyfin-web can direct play it fladder will always transcode it and claim videoNotSupported, audioNotSupport, etc that jellyfin-web didn't have a problem with. This is in the same browser on the same machine. Does anyone else have this problem? How does fladder advertise its codec support to the jellyfin server?