Closed Captioning for Web Video Support with SRT and VTT Files

By Max Wilbert

9 Min Read

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Max Wilbert

Max Wilbert is a passionate writer, live streaming practitioner, and has strong expertise in the video streaming industry.

    Looking for streaming solutions to add subtitles or closed captions to your video project? You’ve come to the right place! In this article, we’ll cover how to do closed captioning for web video.

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

    Captions are key for reaching deaf, hard of hearing, and language-learning populations. Plus, including captions with your video is a legal requirement in some situations. With that context in mind, here’s a breakdown of the topics we’ll cover on closed captioning for web video:

    Table of Contents

    • 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 do closed captioning for web video

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

    First, log in to your Dacast account. Next, navigate to your video-on-demand section. Once there, select the video you want to add the captions to. Lastly, 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. After uploading, click on SAVE and that’s it! You should be able to select your subtitles directly within the player.

    closed captioning for web video

    Next, let’s discuss what types of files to upload.

    Different types of closed captions

    At this point, the question becomes: what exactly should you upload? First, note that 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 preferable, as they are part of the HTML5 standard. However, modern HTML5 live streaming supports both protocols.

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

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

    closed captioning for web video
    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. This standard came on the scene following lawsuits and legislation aimed at making TV programs accessible to people who are deaf and 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. As such, the 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 the user navigate through the video).

    closed captioning for web 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 the text still is valuable in some cases. With that in mind, let’s look at how SRT and VTT files look in text format.


    First, let’s consider SRT. SRT is one of the most useful and widely used formats in the subtitling industry. The format is very simple and easy to create. 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 broadcasters can access later. Having an external file of the text makes it easy for broadcasters 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 minutes, 25 seconds in the video. It would disappear at 5 minutes, 29 seconds exactly. The second subtitle (test subtitle B) would appear at 5 minutes, 29 seconds and 12 frames, and then disappear at 5 minutes and 38 seconds exactly.


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

    Note: users must save VTT files using UTF8 encoding to have characters displayed properly for languages other than English.

    How viewers activate closed captions

    From the viewer’s side, you can manage captions from directly inside the video player. Broadcasters can activate them by clicking a CC (Closed Caption) button located either next to log out (if the content is monetized through a Pay Per View or subscription) or next to the full-screen button.

    By default, closed captions are set to “off”. As a result, turning them on requires clicking the button.

    Captions for live streams

    closed captioning for web video
    Yes, it is also possible to add captions to live video. In fact, it’s something that almost every live TV <a class="dacast-link" href="/why-dacast-to-broadcast-live/">broadcast</a> adds. However, the process is different than what we&#8217;ve described above.</p> <p dir="ltr">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.</p> <p dir="ltr">There are also outsource services like <a class="dacast-link" href="" target="_blank" rel="noopener noreferrer">AI-Live</a> and <a class="dacast-link" href="" target="_blank" rel="noopener noreferrer">Vitac</a>. 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.</p> <h2 dir="ltr">Conclusion</h2> <p>In this post, we&#8217;ve shared several methods of doing closed captioning for web video. Surveys have shown that nearly 1 in 5 Americans are deaf or hard of hearing. Any way you slice it, this is a large, potential audience you could be reaching.</p> <p dir="ltr">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.</p> <p>If you’re ready for <a class="dacast-link" href="/blog/top-10-video-live-streaming-solutions-for-pros/">video live streaming solutions</a> that support modern captions, we think Dacast is a great option to try. But don’t take our word for it. You can try our <strong>14-day free trial </strong>(no credit card required) to test it out yourself. We’d love to help you <a class="dacast-link" href="/stream-live-video-on-your-website/">stream live</a> today!</p> <p style="text-align: left;"><a class="dacast-btn dacast-btn--primary" href="/signup/">YES, SIGN ME UP</a>   </p> <p>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.</p> <p>For exclusive offers and regular <a class="dacast-link" href="/live-streaming-pricing-plans/">live streaming</a> tips, you can also join our <a class="dacast-link" href="" target="_blank" rel="noopener noreferrer">LinkedIn group</a>. Thanks, and good luck with your broadcasts!</p> <p>&nbsp;</p>
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    Max Wilbert

    Max Wilbert is a passionate writer, live streaming practitioner, and has strong expertise in the video streaming industry.

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