Transcoding is the process of taking an input source video in one format and bitrate, and converting it to many output rendition videos with different formats and bitrates such that the video can be played on the majority of the devices in the world at any internet connection speed. Additional details on transcoding can be found in this blog post.
Orchestrators are video miners that are responsible for receiving video from broadcasters and returning transcoded results. They can also be transcoders that transcode video themselves on their own or they can outsource transcoding to separate transcoders. They coordinate work and sometimes perform work on the network.
Transcoders are video miners that are responsible for transcoding video. They perform work on the network.
Stake is LPT that is locked in the Livepeer smart contracts. Orchestrators are required to have stake in order to receive work on the network in order to provide economic security to broadcasters.
Transcoding is performed in individual sessions that are created on orchestrators and transcoders. The definition of a session differs slightly between an orchestrator and a transcoder:
Capacity refers to the total transcoding that an orchestrator or transcoder can provide in an acceptable time frame (i.e. real-time). At the moment, orchestrators and transcoders can set their capacities based on the maximum number of sessions that they can support. For an orchestrator, this maximum session count refers to the maximum number of simultaneous jobs they can receive from broadcasters. For a transcoder, this maximum session count refers to the maximum number of simultaneous transcoding tasks they can receive from broadcasters.