Published on October 13, 2021 (almost 3 years ago)

Support for captions in live videos now available [Crowd cheers louder]

Lamia ChlalaStephanie Tsai
By Lamia and Stephanie4 min readProduct

Today, we’re excited to announce that we’re expanding our caption support to include live video! Adding captions to your live videos makes them more accessible to a wider audience and is a great way to enhance engagement and widen reach. Now, we’ve made it easy for you to connect your live caption provider to Mux and have captions delivered along with your live stream.

LinkImplementing live captions

Before you use this feature, please confirm you are partnered with a live caption provider that can support embedding captions in an RTMP stream using the CEA-608 standard.

💡A little more about CEA-608
CEA-608 stems from the analog where closed captions data was carried in the transmission in a line of video content, but wasn't displayed unless the decoder was told to look for it. These were often referred to as “Line 21” captions. CEA-608 is the most widely adopted and supported standard for transmitting captions within the same stream as audio/video content. (For the sake of simplicity, we’ll just refer generally to captions from here on out.)

Getting started

First and foremost, you’ll need a caption provider. Don’t have one? No worries. Anyone that supports the requirements will work. Here are a few specific partners you can work with:

Have a provider already? If you’re unsure whether they support CEA-608, reach out and confirm it with them.

Once you have an event created with your caption provider, add the embedded_subtitles array to a new stream or an existing live stream. It’s important to note that this can only be configured while the stream is idle.

POST /video/v1/live-streams Request Body { "playback_policy" : [ "public" ], "embedded_subtitles" : [ { "name": "English CC", "passthrough": "English closed captions", "language_code": "en-US", "language_channel": "cc1" } ], "new_asset_settings": { "playback_policy": [ "public" ] } }

Start streaming

Captions will start flowing in once your event starts. Mux will convert the captions into WebVTT, which is supported by most video players.

You can monitor your caption health alongside your live stream on the Live Stream Input Health dashboard. While your event is streaming, you’ll be able to see if Mux is receiving captions from your caption provider. The caption health indicator will help you troubleshoot if issues arise. After the event, the captions are available for download for your review.

Important info

Currently, live captions support a single language per video:

  • English
  • Spanish
  • French
  • German
  • Dutch
  • Portuguese
  • Italian

If you need multi-language support, please let us know. We’d love to hear your feedback.

In addition to this new feature, we’ve also added a new query parameter that lets you enable captions by default for both live and on-demand videos. Simply include default_subtitles_lang as an additional playback modifier with the HLS stream request. Take a look at this guide for more information on how to enable captions by default.

If you need more step-by-step instructions or code samples to get you started, check out our implementation guide here.

Want to learn more? Bonnie wrote a great blog about captions and subtitles, why you should use them, and how to enable captions for on-demand video! Check it out.


There’s no additional cost for adding this feature to your live videos. It’s included for all Mux Video customers. 🎉 In order to add live captions today, you’ll have to configure your streams and opt-in.

We’re excited to be expanding the support of captions to live videos and enabling captions by default. We’re always looking for ways to make it easier for you to build great video that can reach as many people as possible. As always, let us know how else we can improve the experience of using Mux!

Written By

Lamia Chlala

Previously office manager at Zencoder and product marketer at Brightcove. She can often be found geeking out over CSS and experimenting in the kitchen.

Stephanie Tsai

Stephanie comes from Netflix and Brightcove. She likes to travel, eat, and strides to hit her 10,000 steps daily.

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