You can disable and tweak transcoding settings, but it might mean that certain media isnt going to be able to be played at all, if its a certain format. If you have a beefy computer, this shouldnt be an issue, but if not id check this out: https://jellyfin.org/docs/general/server/transcoding/
Well torrents are slow, typically, and unless the video you wanted to watch had i high amount of seeders, that can cause issues. When i use it, i sort by the number of seeders, and then find the highest balance of quality vs seeders.