Join Date: Jan 2005
Location: Scarborough, Ontario
With some Internet searching, I discovered that ID-1 is specified in recommendation EIA-J CPX-1024. (EIAJ is Electronic Industry Association of Japan.) It specifies a way of indicating wide screen content with NTSC video signals.
ID-1 is 14 bits (plus 6 bits of CRC) of information that can be carried on lines 20 and 283 of the NTSC vertical blanking interval. Part of this information indicates 4:3 or 16:9 content.
Since ID-1 is part of NTSC video signals, I presume it could be present on composite, S-video, or component connections. A TV, or other receiving device, capable of detecting and handling it could use it to automatically switch between 4:3 and 16:9 aspect ratios.