Question about decoding

[archangel120]

I am a beginner of Jellyfin. I setup a Jellyfin server on my Synology NAS. And I plan to visit the server from Jellyfin client app of other device and play video. I wonder where is the video file been decoded? From NAS server or on client app device?
If I visite Jellyfin server from web instead of client app, then where is the video file been decoded?

[runzi]

if direct play is not available transcoding will take place on your NAS

[TheDreadPirate]

The client will always have to decode the video, period. However, depending on the client codec support, the server may also become involved.

Direct play = client fully supports the file as is, server simply sends the file
Direct stream = client supports video, but not audio. Server sends video unmodified, transcodes audio.
Transcode = client does not support video. Server transcodes video. Audio may or may not need to be transcoded.