How are CEA-608 closed captions added to standard definition video?
The line 21 which represents the closed captioning data can be added to any full raster standard definition video. Traditionally this was done by a hardware encoder. Now, it can also be inserted directly into a 720×486 video file using closed captioning software, or by taking a “black movie” (a video file containing only line 21 data) generated by a closed captioning service and superimposing it over an existing video. A black movie needs to be generated with specific Row and Column settings depending on the NLE system that it will be used on. Different NLE systems and hardware cards map the line 21 of VBI to a slightly different location within the 720×486 video file, so the Row and Column must be set to match. If the data is in the wrong Row or Column, it might not correctly get mapped to line 21. You can determine the correct Row and Column settings to use by using CPC’s calibration movie: http://www.cpcweb.
The line 21 which represents the closed captioning data can be added to any full raster standard definition video. Traditionally this was done by a hardware encoder. Now, it can also be inserted directly into a 720×486 video file using closed captioning software, or by taking a “black movie” (a video file containing only line 21 data) generated by a closed captioning service and superimposing it over an existing video. A black movie needs to be generated with specific Row and Column settings depending on the NLE system that it will be used on. Different NLE systems and hardware cards map the line 21 of VBI to a slightly different location within the 720×486 video file, so the Row and Column must be set to match. If the data is in the wrong Row or Column, it might not correctly get mapped to line 21.
