broadcast (verb): transmit a programme by radio or TV
buffering (verb): downloading audio/video in preparation for play
live (adjective): being broadcast right now; happening now
on-air (adjective): broadcasting now
streaming (adjective/verb): relating to audio/video being transmitted as a steady, continuous flow
subtitles (noun): words written on a video screen to show what the speaker is saying (subtitles, or subs, may be in the same language as the sound or translated into a different language).
transcript (noun): written version of what you hear on audio/video