The audio elements based on the A/52 ATSC standard and the video elements based
on the ISO/IEC MPEG-2 standard are distributed in digital form using compression and
must be decoded for presentation. The video may be of high definition (HDTV) or of
standard definition (SDTV). The audio may be mono channel, stereo, or multichannel.
Several forms of data complete the main programs of audio and video (e.g. descriptive
texts or commentaries) or may be one or more autonomous services.