Video Grid
Line 21 and digital closed captions are typically transmitted in mono-spaced, fixed width, and height, font.
By default in CC mode, a video grid will be enabled on the player window. The video grid will allow for precise caption positioning and preview in the player.
The grid is superimposed on the video player to help to set or determine the exact text position on the screen. You can turn it off using View > Toggle Video Grid.
Tool Panel
 | Captions style | Allows to set CC styles, such as pop-on, roll-up or paint-on. |
 | Split block | Splits current caption into two parts to allow individual positioning for each part. |
 | Merge block | Merges current split caption into one. |
A ‘split block’ feature will create two sub-captions, each of them can be individually positioned using hotkeys or by dragging the text over the video grid.
Validation Rules
In addition to open subtitles validation checks, Closed Captions mode also enforces captions timing overrun. Timing overrun error means that the caption does not have enough build-up time.
Build-up time, or time to process, represents the number of frames needed to display (transmit) the caption text and the control codes. If it is less, the captions won't be displayed correctly.
If a caption is missing N frames, you can either condense the dialog OR extend the previous caption time by N frames to allow longer processing time for the current one. If the current caption and the previous one are not "chained", the timing overrun error appears because the gap between them is not big enough.
In addition to always-on validation checks, timing overrun events can be detected by running on-demand checks (Subtitle menu > Run checks > Timing Overrun).
Some instances of timing overrun events can be fixed automatically by running a dedicated fix
(Subtitle menu > Run fixes > Timing Overrun).