Closed Captioning for Web Video Support with SRT and VTT Files

Looking for a streaming solution to add subtitles or closed captions to your video project?  This article will go over how it’s done.

Closed Captions (often abbreviated “CC”) are used to convey text information during a video. For example, captions include text and dialogue. But they’ll also provide contextual info about music playing and other important sounds.

Captions are really important for reaching deaf, hard of hearing, and language-learning populations. Plus, including captions with your video is a legal requirement in some situations.

Table of Contents

This article will cover:

  • How to add closed captions to your video
  • Different types of closed captions
  • CEA 608 (“Line 21”) vs. CEA-708 captions
  • How to generate closed captions for your video
  • How viewers activate closed captions
  • Captions for live streams

How to add closed captions to your video

Closed Captioning for Web Video

We’ll begin this article with a description of how to add closed captions to a video on-demand hosted on our video streaming platform.

First login to your DaCast account. Navigate to your video-on-demand section. Then select the video you want to add the captions to. Click over to the “Publish Settings” tab.

On this page, you’ll see a button labeled “Add subtitles.” Click that button, and you can now upload your subtitle files. Next, let’s discuss what types of files to upload.

Different types of closed captions

So now the question is: what exactly to upload? DaCast’s supported caption files include SRT (SubRip Text, aka SubRip Title) and VTT (Video Text Tracks, aka WebVTT) files.

Of the two, VTT captions are preferred, as they are part of the HTML5 standard. However, both protocols are supported for modern HTML5 live streaming.

Both also support multi-language subtitles. For example, you can caption the same video in English, Spanish, Portuguese, and Arabic. In general, go for VTT if you have the option.

CEA-608 (“Line 21”) vs. CEA-708 captions

CEA-608 and CEA-708 are legal standards for closed captioning of TV broadcasts. CEA-608 (sometimes called EIA-608 or “Line 21” captions) is an older standard and was introduced following lawsuits and legislation aimed at making TV programs accessible to people who are deaf or hard of hearing.

CEA-708 is the updated standard, which includes a wider array of features and options. These include support for various alphabets, multiple simultaneous languages, and custom positioning, fonts, and text size and color. 

DaCast supports both CEA-608 and CEA-708. When you add a VTT or SRT file to your DaCast video, it is automatically compatible with CEA-708 caption standards.

How to generate closed captions for your video

Both VTT and SRT are simply plain text files containing information about the video. Information these files incorporate can include:

  • Subtitles (translation)
  • Captions (subtitles along with sound/audio information)
  • Description (describing the video with a screen reader)
  • Chapters (like presentations to help user navigate through the video).

Therefore, it is possible to simply create your captions manually in a text editor. However, there are some free tools available such as Amara that make creating subtitle files easier. Amara and similar platforms also include a marketplace where you can pay someone to caption your videos for a reasonable fee. This market includes translation services as well.

However, editing in text still is valuable in some cases. With that in mind, let’s look at how SRT and VTT files look in text format.


Let’s look at SRT first. SRT is one of the most useful and widely used formats in the subtitle industry. The format is very simple and easy to create, as it originates from the SubRip software program, which uses optical character recognition to extract subtitles and their timings from video files. It then saves them into a text file that can be used later. Having an external file of the text makes it so much more flexible for broadcasters in order to make any future changes to their videos.

SRT Subtitle File Example:

SRT files have an easy to follow layout with some simple structural rules:

SubtitleNumber: 10

StartTime –> EndTime


Blank Line

00100:05:25.000 –> 00:05:29.000

This is a test subtitle A

00200:05:29.000 –> 00:05:32.000

This is a test subtitle B

The example above would make the first subtitle (test subtitle A) appear at 5 minute, 25 seconds in the video. It would disappear at 5 minute, 29 seconds exactly. The second subtitle (test subtitle B) would appear at 5 minute, 29 seconds and 12 frames, and then disappear at 5 minute and 38 seconds exactly.


WebVTT, often shortened to VTT, is another standard for online video. Like SRT, VTT files can be easily formatted in a simple text editor. Here’s an example of a cue in VTT file where three texts are lined with respective to the video.

WEBVTT Kind: captions; Language: en

00:11.000 --> 00:13.000
<v Roger Bingham>We are in New York City

00:13.000 --> 00:16.000
<v Roger Bingham>We're actually at the Lucern Hotel, just down the street

00:16.000 --> 00:18.000
<v Roger Bingham>from the American Museum of Natural History

VTT files must be saved using UTF8 encoding to have characters displayed properly for languages other than English.

How viewers activate closed captions

Closed Captioning for Web Video From the viewer’s side, captions are managed from directly inside the video player. They can be activated via clicking a CC (Closed Caption) button located either next to logout (if the content is monetized through a Pay Per View or subscription) or next to the full screen button.

By default, closed captions are turned off. Turning them on requires clicking the button.

Captions for live streams

It is possible to add captions to live video. In fact, it’s something that’s added to every TV broadcast. However, the process is different than what we’ve described above.

Usually, adding captions involves interfacing with one of two options. First, you could have an in-house captioner. They would use a dedicated machine and caption your live stream, adding a slight delay.

There are also outsource services like AI-Live and Vitac. These platforms provide caption services for live streams for a reasonable fee. They interface with your live stream itself and add the caption to your feed directly.


This article has shared several methods of adding subtitles or captions to your online video. Surveys have shown that nearly 1 in 5 Americans is deaf or hard of hearing. So anyway you slice it, this is a large, potential audience you could be reaching.

As guidelines continue to become stricter on internet streamed content, be sure you are ready to support the formats for the future if required by local or federal law.

If you’re ready for a video live streaming solution that supports modern captions, we think DaCast is a great option to try. But don’t take our word for it. You can try our 30-day free trial (no credit card required) to test it out yourself. We’d love to help you get started with our live streaming today!

secure streaming solution

Do you have questions or comments about any of the topics introduced in this article? We’d love to hear from you in the comment section below. We’ll do our best to get back to you as soon as we can.

For exclusive offers and regular live streaming tips, you can also join our LinkedIn group. Thanks, and good luck with your broadcasts!

2 thoughts on “Closed Captioning for Web Video Support with SRT and VTT Files

  1. Pingback: How to Make Videos with 508 Compliance? - DaCast

  2. Pingback: 2014 a look back at the trends

Leave a Reply

Your email address will not be published. Required fields are marked *