The Complete Guide to Video CaptionsTypes · Formats · Platform Requirements · Best Practices · Tools
Everything a video editor or content creator needs to know about captions — from the difference between closed captions and subtitles, to format specs, reading speed standards, platform requirements, and how to add captions in every major editing tool.
1. Types of Captions
The terms "captions," "subtitles," and "closed captions" are used interchangeably in casual conversation but mean different things in professional delivery. Choosing the wrong type for your platform or audience creates accessibility compliance issues and viewer confusion.
Closed Captions
- Can be toggled on or off by the viewer
- Includes all audio: dialogue, sound effects, music cues, speaker IDs
- Required for accessibility compliance (ADA, FCC, WCAG)
- Delivered as a sidecar file (SRT, SCC, VTT) or embedded in the video container
- Required by most broadcast standards and OTT platforms
Open Captions
- Burned permanently into the video frame
- Cannot be toggled off by the viewer
- Always visible regardless of player or platform
- Required for social platforms that autoplay silently (Instagram, TikTok, LinkedIn)
- Styled by the creator — font, size, position, animation
Subtitles
- Assumes the viewer can hear the audio
- Translates or transcribes dialogue only — no sound effects or speaker IDs
- Used for language translation (foreign-language film, dubbed content)
- Can be closed (sidecar) or open (burned in)
- Not a substitute for accessibility captions
2. Caption File Formats
Different platforms and workflows require different caption file formats. Here is what each format is, what it supports, and when to use it.
| Format | Full name | Best for | Styling |
|---|---|---|---|
| SRTMost common | SubRip Subtitle | YouTube, Vimeo, most online platforms, editing software | Minimal (basic bold/italic tags) |
| VTT | WebVTT | HTML5 video players, web apps, online courses | Basic positioning and styling via CSS |
| ASS/SSA | Advanced SubStation Alpha | Anime fansubs, complex styling workflows, local playback | Full: fonts, colours, animations, positioning |
| SCC | Scenarist Closed Captions | North American broadcast, CEA-608 delivery | Basic — defined by the CEA-608 standard |
| ITT | iTunes Timed Text | Apple TV+, iTunes, Apple platform delivery | Moderate — font, size, colour |
| TTML/DFXP | Timed Text Markup Language | Netflix, BBC iPlayer, enterprise streaming platforms | Extensive — W3C standard for rich captions |
| SBV | SubViewer | YouTube (alternative to SRT) | Minimal |
3. Reading Speed and Character Limits
Captions that appear too quickly to read, or that cram too many words per line, are worse than no captions at all. Every major broadcaster and streaming platform publishes reading speed and line length standards. Here are the ones that matter.
Netflix
- Maximum 42 characters per line
- Maximum 2 lines per caption
- Maximum 20 characters per second (CPS)
- Minimum display time: 5/6 seconds
- Maximum display time: 7 seconds
BBC
- Maximum 37 characters per line
- Maximum 2 lines per caption
- Maximum 160–180 words per minute
- Minimum display time: 1 second
- Programme-dependent reading speed guidance
YouTube / General web
- No strict standard — follows viewer preference
- Recommended: 42 characters per line
- Recommended: 2 lines maximum
- 17 CPS is a common readable threshold
- SRT or VTT format accepted
Social platforms (Instagram, TikTok)
- Open captions — no format standard
- Shorter lines preferred for mobile (20–28 chars)
- Large font size for vertical video
- One to two lines maximum
- High contrast text essential for outdoor viewing
4. Platform Caption Requirements
Each distribution platform has different caption format requirements and delivery workflows. Here is what each major platform accepts and expects.
YouTube
Accepts: SRT, VTT, SBV, SCC, TTMLHow: Upload via YouTube Studio > Subtitles, or let YouTube auto-generate (lower accuracy)
Captions improve YouTube search indexing. Auto-generated captions should always be reviewed.
TikTok
Accepts: Open captions (burned in) or TikTok's in-app auto-captionsHow: No sidecar file upload. Use open captions burned into the video, or enable TikTok's Auto Captions in the app.
TikTok auto-captions have limited language support and variable accuracy.
Instagram Reels
Accepts: Open captions (burned in) or Instagram's in-app auto-captionsHow: Burn captions into the video before upload. Instagram does not accept sidecar caption files.
85% of Instagram video is watched without sound — open captions are essential.
How: Upload an SRT file alongside native video posts. LinkedIn has supported SRT upload since 2022.
LinkedIn audiences skew professional — accurate captions affect perceived content quality.
Vimeo
Accepts: SRT, VTT, SCC, DFXP/TTMLHow: Upload via video manager > Subtitles & Captions tab after uploading the video.
Vimeo Pro and Business plans support multiple caption languages per video.
Netflix
Accepts: TTML (IMSC 1.1), DFXPHow: Delivered via Netflix's partner delivery portal. Requires Netflix's full caption specification compliance.
Netflix has strict QC standards including reading speed checks, character limits, and style guides per territory.
Facebook / Meta
Accepts: SRT sidecar or open captionsHow: Upload SRT file via video settings in Facebook Business Suite. Or burn captions in.
Facebook native video with captions outperforms video without captions in reach and engagement.
5. Caption Best Practices
Good captions are transparent — the viewer reads them without noticing the formatting. Bad captions pull attention away from the content. These are the rules that separate professional caption delivery from amateur subtitle output.
Break lines at natural language boundaries
Break between subject and predicate, or between clauses. Never break mid-phrase or between an adjective and the noun it modifies. Wrong: "The quick brown / fox jumped." Right: "The quick brown fox / jumped over the fence."
Keep lines under 42 characters
Longer lines require wider screens or smaller font sizes to display correctly. 42 characters per line is the professional broadcast standard and ensures readability on most screen sizes.
Use a maximum of two lines
Three-line captions cover too much of the screen and are harder to read while watching the image simultaneously. If a cue requires three lines, split it into two cues.
Maintain minimum display time
A caption cue should display for at least one second, even for very short phrases. Cues that flash on screen too briefly cannot be read. Aim for a minimum of 1–1.5 seconds per cue.
Synchronise to audio onset, not transcript structure
Caption cues should appear when the word is spoken, not a sentence before or after. Viewers match what they hear to what they read — sync drift breaks immersion immediately.
Identify speakers in multi-person content
For interviews, panel discussions, and podcasts, prefix each speaker's dialogue with their name in brackets: [SARAH] or use a hyphen for alternating speakers. This is required for accessibility-grade closed captions.
Describe meaningful non-speech audio
For accessibility-grade closed captions, include descriptions of relevant non-speech audio in brackets: [door slams], [upbeat music], [crowd applause]. Subtitles skip this — closed captions require it.
Keep punctuation consistent
Use an ellipsis (...) for natural pauses only, not at the end of every cue. Use a capital letter at the start of each new sentence even if it continues in the next cue. Follow the script's language punctuation rules, especially for RTL languages.
6. How to Add Captions in Your Editing Software
Each video editing platform handles captions differently. Here are complete step-by-step guides for every major NLE.
Adobe Premiere Pro
Two methods: built-in Speech to Text (limited languages) and CaptionX plugin (57+ languages, native timeline integration). Covers export as sidecar SRT and open caption burn-in.
Read full guideDaVinci Resolve
Subtitle track, SRT import via File > Import > Subtitles, Auto Caption (English, Resolve 18+), RTL language setup, CJK font guidance, and Deliver page export options.
Read full guideFinal Cut Pro
Captions role system, SRT/SCC import, Auto Transcribe (FCP 10.6.5+), format selection (SRT, CEA-608, ITT), sidecar export vs burn-in, and common export issues.
Read full guideCapCut
Auto Captions, manual text entry, Apply to All styling, burn-in export for TikTok and Reels. Includes an honest breakdown of CapCut's limitations for professional workflows.
Read full guide7. Free Caption Tools
A set of free browser-based tools for common captioning tasks. All run locally — no upload, no account required.
SRT Timing Adjuster
Fix out-of-sync captions by shifting all timestamps by a fixed positive or negative offset.
Open toolSRT Merger
Combine two SRT files into one with automatic timestamp offsetting for the second file.
Open toolSRT to VTT
Convert SRT subtitle files into WebVTT for HTML5 players and web platforms.
Open toolVTT to SRT
Convert WebVTT files back into SRT format for editing software and platform uploads.
Open toolSRT to TXT
Extract plain text transcript from an SRT file by stripping timestamps and cue numbers.
Open toolSRT to ASS
Convert SRT files into ASS subtitle format for advanced styling and local playback.
Open toolSRT to JSON
Convert SRT subtitle cues into structured JSON for developers and automation workflows.
Open toolPodcast to Captions
Generate caption files from podcast audio files and export as SRT or VTT.
Open toolLyrics to Captions
Convert song lyrics to timed caption files for music videos.
Open tool8. Frequently Asked Questions
What is the difference between closed captions and subtitles?
Closed captions include all audio information — dialogue, sound effects, music cues, and speaker identification — and can be toggled on or off by the viewer. Subtitles assume the viewer can hear the audio and only transcribe or translate spoken dialogue. Closed captions are required for accessibility compliance. Subtitles are primarily for language translation.
What is the maximum number of characters per line for captions?
The most widely used standard is 42 characters per line (Netflix, BBC, and most broadcast standards). Some platforms use 32 characters per line for stricter readability. Captions should never exceed two lines. For social media where captions appear on mobile screens, shorter lines of 20–32 characters are often more readable.
What caption format should I use for YouTube?
YouTube accepts SRT, VTT, SBV, and several other formats. SRT is the most universally compatible and the safest choice for YouTube uploads. Upload via YouTube Studio > Subtitles.
What is a good caption reading speed?
The standard reading speed is 160–180 words per minute for general audiences. In characters per second, 17 CPS is the standard broadcast threshold. Netflix allows up to 20 CPS. Caption cues that exceed the reading speed should be split into shorter segments.
Do captions improve YouTube SEO?
Yes. YouTube indexes caption text as part of its search ranking algorithm. Accurate captions increase the amount of searchable text associated with your video, improving discoverability. Uploaded SRT files are more accurate and more reliably indexed than YouTube's auto-generated captions, particularly for non-English content.
Are captions required by law?
In many jurisdictions, yes. In the United States, the Americans with Disabilities Act (ADA) and Section 508 require captions for video content produced by government entities and many businesses. The FCC requires closed captions on all broadcast television content. UK Ofcom requires captions on 90% of broadcast programming. Online video regulations vary by country and are evolving rapidly.
What is the difference between SRT and VTT?
SRT (SubRip) is the most widely supported caption format and uses comma-based milliseconds and numbered cue blocks. VTT (WebVTT) is built for the web, uses period-based milliseconds, starts with a WEBVTT header, and supports additional features like positioning and CSS-based styling. SRT is the better choice for editing software and most platforms. VTT is the better choice for HTML5 video and web apps.
Working in Adobe Premiere Pro?
CaptionX adds accurate captions to your timeline in seconds
No SRT juggling. No app switching. CaptionX is a native Premiere Pro plugin that generates captions directly on your timeline in 57+ languages — free to start, no credit card required.