Codec(code + decode)
Because of the video file is very big, so need code(compress) the file to it smaller. when playing the file, decode the video to play. Common video encoding format: H264, VP8, mpeg4, msmpeg4v2... Common audio encoding format: aac, ac3, DTS, mp3, vorbis...
a file format store codeced file, can contain multi streams(video stream, audio stream, subtitle stream). Common video format: mkv, mp4, webm, mov, flv, avi... Common audio format: mp3, aac, ac3, ogg, wma...
Demux: use demuxer parse the different stream from container. Mux: use muxer into the different stream according to rules to container.