User`s guide

74
MPEG-2 (DTV/ATSC)
MacCaption software has been able to add closed captions to MPEG-2 video used in the
authoring of DVDs for a number of years but recently CPC has successfully implemented a way
to embed both 608 and 708 closed captions in DTV/ATSC MPEG-2 video for both 4:3 and 16:9
formats. TV Transmissions over the air in the U.S. and Canada is basically MPEG-2 streams so
the concepts here will work for HD as well as SD MPEG-2 video.
Captions can be added to generic MPEG-2 Elementary and Program streams. The MPEG-2 can
be SD or HD. Captions can be formatted in any one of the following styles: ATSC 608/708,
DVD, CCube/LSI DVx 608 Linear or CCube/LSI DVx 608 Temporal and Sigma Streams with
Line-21. To add captions to Transport Streams please see the section in the manual that talks
about encoding with Manzanita software.
In MPEG-2 video closed captions are carried in User Data packets in the MPEG data stream.
There are three distinct closed caption data formats used in MPEG video:
• One format is used for encoding CCs into MPEG data that will be used as video
assets in DVD authoring;
• A second format is used for Digital Television (DTV) and carries EIA 608 and
formatted closed captioning data;
• A third format is used for encoding DTV EIA 708 closed captioning data. This is the
same as HD. (SD MPEG-2 streams can also carry 708 data)
The MacCaption software supports adding closed captions to DTV MPEG video; and CPC is
researching adding EIA 708 closed captions into DTV baseband HD-SDI. At present the current
MacCaption software can decode EIA 708 closed captions from both MPEG-2 video and HD-
SDI captured QuickTime clips from the Matrox MXO2.
MacCaption will decode and encode standard MPEG-2 closed caption User Data packets in
video encoded with the Vela Research MPEG hardware, http://www.vela.com.
MacCaption can also decode the SCTE 20 608 closed caption specification from MPEG-2
streams. To decode this style of closed caption data go to File>Import>SCTE 20 608 Closed
Captions.
The DVD and DTV 608 closed caption formats both conform to the EIA 608 standard
specification for closed caption data encoding, but they differ in their physical positioning and
bit coding layout in the MPEG data stream. The DTV 608 and the DTV 708 formats differ in
their standard specifications for closed caption data encoding, but they are transmitted together
and in the same User Data packet in the MPEG data stream. Therefore, MacCaption can add
both 608 and 708 closed captions to the one MPEG-2 file. This feature guarantees compatibility
with both HDTV sets and standard definition TV sets that receive DTV transmission through
converter boxes.
DTV 608 closed caption data that is inserted into MPEG video is typically copied directly from
its analog standard definition video EIA 608 closed caption counterpart.