National Datacast Incorporated (NDI) was a pioneer indata broadcasting.[1]It was a for-profitsubsidiary of thePublic Broadcasting Service (PBS), which had a minority stake in the final years of this subsidy. It handleddatacasting on PBSTV stations throughout theUnited States.[1] Services usingATSCdigital TV includedMovieBeam andUpdateTV. UpdateTV continues to be operated by its present owner,Qterics,leasingbandwidth to other companies for the purpose of automatic television firmware updates.
National Datacast was formed in 1988 based on PBS' early work inclosed captioning for the hearing impaired.[1]
It usedNTSC horizontal line 21, which is at the end of thevertical blanking interval, and thus, potentially visible as blinking black and white bars at the top of the screen in theoverscan area. This artifact can often be seen when viewing old footage on modern televisions or PCs that no longer crop the overscan area. Uniquely, NDI may also have used other horizontal lines in the vertical blank for other types of data transmission.[1]
It ceased operations in 2015.[2]
