Captioning & subtitling

Caption QC & Conformance

A caption file can look perfect in an editor and still fail on a broadcast decoder. I run an independent QC pass that decodes both CEA-608 and CEA-708, checks positioning, reading order, timing and spec conformance with caption-inspector, CCExtractor and ffmpeg, then redeliver corrected files with a decode report.

✓ Independent 608 + 708 decode✓ caption-inspector, CCExtractor, ffmpeg✓ Corrected files + report
Dao Huy (Lucas)

Dao Huy (Lucas)

Subtitle & caption specialist, Da Nang, Vietnam

BA in EnglishIELTS 7.0HSK 5Upwork Top-Rated Plus4.99/5 from 80 reviewsTop 1%7+ years, 200+ projects
Recently delivered English SDH for six episodes (around 160 minutes) with true CEA-608 and CEA-708 embedded and independently QC-verified, for a US media-localization agency.
After
This line is clean and on time.
Before
timecode drift +8f, 61 chars/linethis caption line is far too long and it arrives eight frames late after the cut

Drag to compare the flagged caption and the corrected two-liner.

The checks a QC pass runs, and the spec each is measured against.
01

What a caption QC pass checks

An independent QC pass decodes the file the way a broadcaster's system will, not the way your editor shows it. These are the checks and the tools behind them.

CheckWhat can go wrongTool
608 / 708 decodeSingle-track fallback, garbled textcaption-inspector
PositioningCovers the lower-thirdcaption-inspector, ffmpeg
Reading speedToo fast to followSubtitle Edit
Timing and syncDrift after a cutCCExtractor, ffprobe
Spec conformanceFails the target profileInterra Baton (compat)
02

What an editor preview hides

A caption file can pass in the tool that made it and still fail on air. Using a separate decoder is what catches it.

In the authoring tool
On an independent decoder
01608 and 708 look identical
I decode each track on its own; a broken 708 often hides behind a fine 608.
02Positioning looks clear
The decoder places it over the lower-third. I check against the real frame.
03Timing looks synced
Drop-frame math shifts it. I verify timecode on the actual media.
04The file passes
It passes that one tool. I re-decode with caption-inspector, a separate engine.

What you receive

caption-inspector decode report (608 + 708)
Positioning and conformance notes
Corrected SCC, MXF or XML redelivery
Sign-off preview MP4

Spec checklist

✓Independent CEA-608 and CEA-708 decode
✓Positioning and reading-order checks
✓Timing, gap and duration validation
✓Spec conformance against the target profile
✓Toolchain: caption-inspector, CCExtractor, ffmpeg, Subtitle Edit, Aegisub, Adobe Premiere Pro
✓Corrected files redelivered with a report

Toolchain

  1. Probe

    Built withFFprobe

  2. Extract

    Built withCCExtractor · caption-inspector

  3. Conform

    Built withSubtitle Edit
    Compatible withInterra Baton · Telestream Vidchecker · Venera Pulsar
Standards
FCC caption rulesCEA-608 / 708WCAGEBU-TT

How it works

1

Scope and spec

You send the video and target profile. I confirm frame rate, timecode, caption style and the delivery formats you need.

2

Author

I time and write the captions or subtitles to the reading-speed, line-length and positioning rules for the target.

3

Encode and wrap

I produce the deliverables: SCC, MXF OP1A embed, SMPTE ST 2052-1 or DCP XML, plus a burned-in preview.

4

QC and deliver

I decode the result independently with caption-inspector, fix anything that drifts, and deliver with a report.

Three-layer QC before anything ships

Broadcast and cinema files fail on decoders, not in an editor preview. Every delivery goes through three passes and an independent decode.

1. Rough pass

Spot and draft every caption against the script, source audio and shot changes.

2. Alignment and timing

Tune reading speed, line breaks and positioning; align to shot changes and clear names and lower-thirds.

3. Independent senior QC

Decode the result on a separate decoder, check conformance to the target spec, and sign it off.

✓Characters-per-second held to spec on every event
✓Safe-title and safe-area violation check per caption
✓Multi-device and projection playback testing
✓Independent CEA-608 and CEA-708 decode with caption-inspector
NDA and secure handling for unreleased films and pre-air episodes; screeners are deleted on delivery.

Indicative rate

Per project or per hour

✉ Request a quote

Related captioning services

Captioning & subtitling →Closed Captions →SDH Captions →DCP Subtitles →Subtitle Translation →Vertical Subtitles →Vietnamese translation →

Frequently asked questions

What do you check in a caption QC pass?

I decode the 608 and 708 tracks independently, then check text accuracy, reading order, positioning over lower-thirds, timing, event gaps and durations, and conformance to the target spec (broadcast SCC/MXF or a DCP profile).

Which tools do you use?

caption-inspector (the Comcast open-source decoder) for an independent 608/708 read, plus CCExtractor, ffmpeg, Subtitle Edit, Aegisub and Adobe Premiere Pro. Using a decoder that is separate from the authoring tool is what catches problems an editor preview hides.

Can you fix the problems you find, not just report them?

Yes. I redeliver corrected SCC, MXF or subtitle XML alongside the decode report, so the file is ready to air, not just documented.

✉ Request a quote

⏱ Typical response within 10 minutes

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