CEA-608
Line 21 closed captions — FCC broadcast standard
CEA-608 (Line 21) is the FCC-mandated closed-caption standard for US broadcast TV and cable. Still required in MP4/MXF deliverables for ABC, NBC, CBS, FOX, and cable operators in 2026. CEA-708 is the digital successor — most deliverable specs require both.
In depth
CEA-608 (also called Line 21 captions) is the closed-caption standard developed for analog NTSC television in the 1980s. It encodes caption data in line 21 of the vertical blanking interval — a technique that predates digital broadcasting. Modern usage: CEA-608 lives on as an embedded sidecar track inside MP4, MXF, and MPEG-TS broadcast deliverables. Most US broadcast networks (ABC, NBC, CBS, FOX) and cable operators still require CEA-608 and CEA-708 caption tracks on all submitted programming. CEA-708 is the digital successor and nearly all modern deliverable specs include both.
When to use it
Use CEA-608 when delivering to US broadcast TV or cable operators — it's required by FCC mandate for all broadcasters. For streaming, web, social, and OTT, prefer SRT, VTT, or IMSC/TTML — CEA-608's character set, styling, and positioning are too limited for modern workflows.
Frequently asked
What is CEA-608?+
CEA-608 (Line 21) is the original US closed-caption standard for analog NTSC television, developed in the 1980s. It encodes caption text in line 21 of the vertical blanking interval. It's still required by the FCC for US broadcast TV and appears as an embedded track in modern MP4 and MPEG-TS broadcast deliverables.
What's the difference between CEA-608 and CEA-708?+
CEA-608 is the analog NTSC standard, limited to 32 characters per line, a narrow color palette, and two caption channels per field. CEA-708 is the digital ATSC successor — it supports richer styling, more languages, larger character sets, and multiple service channels. Most US broadcast deliverables require both embedded in the same file.
Do I need CEA-608 for YouTube or social media?+
No — YouTube, TikTok, LinkedIn, and other platforms use SRT or VTT. Don't submit CEA-608 directly to these platforms. If you have a CEA-608 source file, extract the caption text and re-export as SRT before uploading.
How do I convert CEA-608 captions to SRT?+
Use a broadcast extraction tool (CCExtractor is free and open-source) to pull the Line 21 data from your MP4 or MPEG-TS file and export as SRT. Most NLEs (Premiere, DaVinci) can also read embedded CEA-608 tracks and export them as SRT.
Captions that the viewer can toggle on or off, typically delivered as a separate text track encoded into or alongside the video.
An XML-based subtitle format used by streaming services and broadcast workflows. Powerful styling and positioning, but verbose.
The most common subtitle file format. Plain text with numbered cues and HH:MM:SS,mmm timestamps.