How does Jellyfin live transcoding?

[theprof]

How does Jellyfin do live transcoding?

Basically, how is FFMPEG doing the realtime transcoding meanwhile the client's browser is able to fast forward/seek in terms of HTTP?

I'm able to pipe the FFMPEG transcoding output to the browser HTML5 video. However, it keeps downloading and increasing the duration during the playback so it's possible to seek to a specific minute mark until the whole video has been downloaded. How does Jellyfin do it?

[TheDreadPirate]

On a decently spec'd system, ffmpeg is transcoding faster than real time and building up a buffer. If you skip to a part that already has been transcoded, Jellyfin will send the segment from that time stamp. If you skip to a portion of the video where ffmpeg has not yet transcoded, ffmpeg will be restarted at that time stamp and there is usually a noticeable delay of a few seconds for this situation.