SPRUIE9D May 2017 – May 2024 DRA74P , DRA75P , DRA76P , DRA77P
Digitized video is based on scan lines in found in analog video. BT.601 uses various sync signals to specify when a new field and a new line starts. BT.656 and BT.1120 uses sync words embedded in the data stream to specify start of field and start of line.
An image can be digitized into regions shown in Figure 11-19.
With the capability to encode sync words inside the data stream, there is more flexibility for adding non-video related data, called Ancillary Data. Also, code words embedded in the digital stream can be used as a type of identifier for multiplexing several sources of video into one data stream.
Figure 11-20 shows End-of-Active-Video (EAV) and Start-of-Active-Video (SAV) code words added to a video transmission. The period between the EAV and SAV is equivalent to Horizontal Blanking. The period between the SAV to the next EAV is active video or vertical blanking.
In the BT.656 or BT.1120 embedded code word scheme, three bits of the EAV/SAV code word are important: F (field), H (horizontal blanking), and V (vertical blanking).
Figure 11-21 shows the values of F, V, and H flags at different locations in the picture. The Field flag represents the state of the Field ID for the picture. For progressive frames, F is always ‘0.’ The V flag specifies vertical blanking areas. The H flag specifies horizontal blanking portions of the picture.