Scenarist Closed Caption (SCC)

What is an SCC file?

SCC (Scenarist Closed Caption) is the standard file format for CEA-608 closed captions, the “line 21” caption system used across North American television. The format comes from Sonic Solutions’ Scenarist DVD authoring software. It has since become the default sidecar caption file for broadcast, cable, and many streaming and video-on-demand platforms.

An SCC file doesn’t contain readable text. Each line holds a SMPTE timecode followed by hexadecimal byte pairs, which are the same 608 data a caption encoder would insert into the video signal. Some byte pairs are characters. Others are control codes that tell the decoder where to place text, when to show it, and how to style it. That is why an SCC file looks like 9420 9420 94ae instead of dialogue, and why it can describe roll-up and paint-on captions as well as ordinary pop-on blocks.

Because SCC is a direct encoding of CEA-608, it inherits the standard’s limits. Captions sit on a grid of 15 rows by 32 columns. The character set is a fixed set of Latin characters, and there are only a few colors and attributes. In return, SCC is exact: what is in the file is what the decoder will display.

Scenarist_SCC V1.0

00:00:01;00	9420 9420 94ae 94ae 9470 9470 c845 4c4c 4f80 942f 942f

00:00:04;00	942c 942c

Reading the sample

• 9420 means Resume Caption Loading, which starts a pop-on caption in off-screen memory.
• 94ae means Erase Non-Displayed Memory, which clears that off-screen buffer.
• 9470 is a preamble address code that places the cursor on row 15, column 0.
• c845 4c4c 4f80 is the text “HELLO” as 7-bit characters with odd parity. 80 is padding.
• 942f means End of Caption, which swaps the buffer on screen. 942c erases the displayed caption.

Control codes are normally sent twice, so a decoder that misses one transmission still acts on the command.