Audio and Video Linking
Audio codecs can usually contain one audio channel (mono), two audio channels (stereo), or more channels (e.g. "5.1" surround). For example, human voice is recorded using one channel while music uses in general two or more channels. The quality will vary depending on the bitrate, ie the number of bits used per unit of playback time.
Video codecs will contain a sequence of frames, ie still pictures and, for compressed formats, movements between those pictures. Quality will vary depending on the number of frames per second, color space, resolution, etc.
Media storage formats will contain audio codec streams, video codec streams, captions, and meta information. It combine them to provide the audio or the video, with alternative or enhanced materials. In general a video will have one video codec stream, one or more alternative audio codec streams, and may have captions and meta information.