{"id":1125,"date":"2026-06-10T09:43:25","date_gmt":"2026-06-10T02:43:25","guid":{"rendered":"https:\/\/liveapi.com\/blog\/how-to-add-closed-captioning-to-a-video\/"},"modified":"2026-06-10T09:43:53","modified_gmt":"2026-06-10T02:43:53","slug":"how-to-add-closed-captioning-to-a-video","status":"publish","type":"post","link":"https:\/\/liveapi.com\/blog\/how-to-add-closed-captioning-to-a-video\/","title":{"rendered":"How to Add Closed Captioning to a Video: Methods, Formats, and Code"},"content":{"rendered":"Reading Time: <\/span> 10<\/span> minutes<\/span><\/span>

Roughly 85% of videos on social platforms are watched with the sound off, and about 1 in 5 people experience some degree of hearing loss. Captions cover both groups at once \u2014 they make your content readable on a muted phone in a noisy room and accessible to viewers who are deaf or hard of hearing. They also give search engines text to index, which helps your videos rank.<\/p>\n

This guide shows you how to add closed captioning to a video three ways: by hand, with automatic speech recognition, and through an API for apps that serve video at scale. You’ll see the caption file formats that matter, the exact steps for popular platforms, and the code needed to attach captions to an HLS<\/a> stream so they play correctly across devices.<\/p>\n

What Is Closed Captioning?<\/h2>\n

Closed captioning is a text version of the spoken audio and relevant sounds in a video that viewers can turn on or off. The word “closed” means the captions live in a separate track or file and stay hidden until the viewer enables them \u2014 unlike open captions, which are burned into the video frames and always visible.<\/p>\n

Closed captions include more than dialogue. A proper caption track also describes speaker changes, music cues, and sound effects like [APPLAUSE] or [DOOR SLAMS], because the viewer may not hear them at all. That distinction matters for accessibility compliance and for the experience of deaf and hard-of-hearing audiences.<\/p>\n

Closed Captions vs Subtitles vs Open Captions<\/h3>\n

People use these terms interchangeably, but they describe different things. The table below breaks down the differences.<\/p>\n\n\n\n\n\n\n\n
Type<\/th>\nToggle on\/off?<\/th>\nIncludes sound effects?<\/th>\nPrimary purpose<\/th>\n<\/tr>\n<\/thead>\n
Closed captions<\/td>\nYes<\/td>\nYes<\/td>\nAccessibility for deaf\/hard-of-hearing viewers<\/td>\n<\/tr>\n
Open captions<\/td>\nNo (burned in)<\/td>\nYes<\/td>\nGuaranteed display where toggling isn’t supported<\/td>\n<\/tr>\n
Subtitles<\/td>\nYes<\/td>\nNo (dialogue only)<\/td>\nTranslation for viewers who can hear but don’t speak the language<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

In short: captions assume the viewer can’t hear the audio, while subtitles assume they can hear but need a translation. Apple labels accessibility-focused tracks “SDH” (Subtitles for the Deaf and Hard of hearing). If you want a deeper breakdown, see our guide on closed captioning vs subtitles<\/a>.<\/p>\n

Caption File Formats You Need to Know<\/h2>\n

Before you add closed captioning to a video, you need the captions in a file format your player or platform accepts. Four formats cover almost every workflow.<\/p>\n\n\n\n\n\n\n\n\n
Format<\/th>\nExtension<\/th>\nStyling support<\/th>\nBest for<\/th>\n<\/tr>\n<\/thead>\n
SubRip<\/td>\n.srt<\/code><\/td>\nMinimal<\/td>\nUploads to YouTube, Facebook, LinkedIn<\/td>\n<\/tr>\n
WebVTT<\/td>\n.vtt<\/code><\/td>\nPositioning, color, fonts<\/td>\nHTML5 video and HLS streaming<\/td>\n<\/tr>\n
TTML \/ IMSC<\/td>\n.ttml<\/code>, .xml<\/code><\/td>\nRich layout<\/td>\nBroadcast and DASH workflows<\/td>\n<\/tr>\n
CEA-608\/708<\/td>\nEmbedded<\/td>\nLimited (608), rich (708)<\/td>\nBroadcast TV and in-band streams<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

SRT<\/strong> is the most widely accepted upload format. It’s plain text with sequential numbers, start\/end timecodes, and the caption line. Most social and hosting platforms accept it directly.<\/p>\n

WebVTT<\/strong> (Web Video Text Tracks) is the format for the modern web. It’s the only caption format the HTML5 <track><\/code> element supports natively, and it’s the standard for captions delivered inside HLS streams. WebVTT files must be UTF-8 encoded and start with a WEBVTT<\/code> header line. Our VTT vs SRT comparison<\/a> covers when to pick one over the other.<\/p>\n

CEA-608 and CEA-708<\/strong> are the legacy broadcast standards, embedded directly in the video signal rather than carried as a sidecar file. You’ll mostly encounter them when ingesting broadcast feeds or converting them to WebVTT for web delivery.<\/p>\n

Here’s what a minimal WebVTT file looks like:<\/p>\n

WEBVTT\n\n00:00:01.000 --> 00:00:04.000\nWelcome to the live stream.\n\n00:00:04.500 --> 00:00:07.200\n[upbeat music]\n\n00:00:07.500 --> 00:00:10.000\nToday we're shipping captions.\n<\/code><\/pre>\n
The SRT equivalent is nearly identical, but uses comma decimal separators and numbered cues:<\/p>\n
1\n00:00:01,000 --> 00:00:04,000\nWelcome to the live stream.\n\n2\n00:00:04,500 --> 00:00:07,200\n[upbeat music]\n<\/code><\/pre>\n
Three Ways to Add Closed Captioning to a Video<\/h2>\n
There are three practical methods, and the right one depends on how many videos you handle and where they’re delivered.<\/p>\n\n\n\n\n\n\n\n
Method<\/th>\nSpeed<\/th>\nAccuracy<\/th>\nBest for<\/th>\n<\/tr>\n<\/thead>\n
Manual<\/td>\nSlow<\/td>\nHighest<\/td>\nOne-off videos, exact compliance<\/td>\n<\/tr>\n
Automatic (ASR)<\/td>\nFast<\/td>\n85\u201395%<\/td>\nBulk libraries, social clips<\/td>\n<\/tr>\n
API \/ programmatic<\/td>\nFast at scale<\/td>\nDepends on source<\/td>\nApps and streaming platforms<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
The next three sections walk through each in order.<\/p>\n
How to Add Closed Captioning to a Video Manually<\/h2>\n
Manual captioning gives you the most accurate result because a human writes and times every line. The trade-off is time \u2014 expect roughly 4 to 6 minutes of work per minute of video. Here are the steps.<\/p>\n
    \n
  1. Transcribe the audio.<\/strong> Play the video and type out every spoken line, plus sound effects and speaker labels. Keep each caption to one or two lines so it fits on screen.<\/li>\n
  2. Add timecodes.<\/strong> Note the start and end time for each caption in HH:MM:SS,mmm<\/code> format. Captions should appear as the words are spoken and stay on screen long enough to read \u2014 usually 1 to 6 seconds.<\/li>\n
  3. Save as an SRT or VTT file.<\/strong> Use a plain-text editor \u2014 TextEdit on Mac (in plain-text mode) or Notepad on Windows. Save with the .srt<\/code> or .vtt<\/code> extension and UTF-8 encoding.<\/li>\n
  4. Upload the file alongside your video.<\/strong> Most platforms have a “subtitles\/CC” option where you attach the file. The platform syncs it to the video using the timecodes.<\/li>\n<\/ol>\n
    This approach works well for a handful of videos where accuracy is non-negotiable, such as legal, medical, or training content.<\/p>\n
    How to Add Closed Captions Automatically<\/h2>\n
    Automatic speech recognition (ASR) generates a caption track from the audio in minutes. Modern engines hit 85\u201395% accuracy on clear audio, which is good enough for a first draft you then correct.<\/p>\n
    The workflow is consistent across tools:<\/p>\n
      \n
    1. Upload the video to a captioning service or platform with built-in ASR.<\/li>\n
    2. The engine transcribes the audio and generates timed captions.<\/li>\n
    3. Review and edit the output \u2014 fix names, technical terms, and any spots where multiple people talk at once.<\/li>\n
    4. Publish the corrected track or export it as an SRT\/VTT file.<\/li>\n<\/ol>\n
      Cloud speech APIs power most of these tools under the hood. Google Cloud Speech-to-Text, AWS Transcribe, and Azure Speech all return word-level timestamps you can convert into WebVTT cues. If you’re building this into your own product, you’d extract the audio with a tool like FFmpeg, send it to the speech API, and format the response as a caption file.<\/p>\n
      Always review automatic captions before publishing. ASR struggles with proper nouns, accents, overlapping speakers, and background noise \u2014 exactly the details that matter for accessibility.<\/p>\n
      How to Add Captions on Popular Platforms<\/h2>\n
      If you’re publishing to a hosted platform rather than your own app, each one has its own caption upload flow. Here are the most common.<\/p>\n