Live Captions: Schedule Live Captions for an RTMP Stream with captions delivered in any video player - BETA


Once the Live Captioning module has been activated within 3Play Media, follow the steps below to schedule captions for an event. In this workflow you will stream from your video source (encoder) to 3Play. From there, 3Play will encode captions into your video stream, and then send that video stream with captions to your specified Restream URL.

Note that events default to US-Eastern time unless a new timezone has been configured at the user level and configured for users outside of the US-Eastern time zone.


Click into the Live Captioning module within your 3Play Media project, and select “I want to caption another RTMP stream.”




Select Event Start Time

Click the calendar icon to choose the MM/DD/YYYY and HH:MM:SS of the event. The time will automatically be set to the current time but can be manually edited within the field.

Please note: The live event must be scheduled at least 5 minutes in the future and it is editable up until 5 minutes prior to the scheduled start time. If you need to edit your event within 5 minutes of the event start, please cancel or end the original order and create a new event. 3Play will initiate a service to listen for your stream at this time. Do not attempt to stream to 3Play before the event start time, as the stream connection will fail to connect from your encoder to 3Play and your encoder will display an error message.




Add Event Name (optional)

Edit the event name if desired. If not edited, the default event name will be "Live Stream at [today’s date].”


Streaming to 3Play from your encoder 

To allow 3Play to receive your stream and create captions, you will stream to 3Play's caption service from your encoder. As a default, 3Play will provide you with a stream target (transcoder). The RTMP URL address and Key to the stream target are provided on the confirmation page of this workflow; you'll enter this information into your encoder stream settings in preparation for the event.

If you prefer to use your own transcoder, please check the box “Override 3Pay-provided RTMP URL and key” and enter your own RTMP URL and key information in the fields provided.






Provide a Wordlist (optional)

To improve accuracy of automated captions for a scheduled Live Captioning event, add a Wordlist of the proper nouns, terms, and phrases unique to your organization that may be commonly used during the event. 

Click to learn more information regarding Wordlists for Live Captioning Events





Adjust Advanced Settings (optional)

Advanced settings will allow you to adjust caption latency, filter offensive words, event wait time, max event time, elect to save the video stream, and destination folder where your files will be saved post-event. 

Click to learn more about Advanced Settings for Live Captioned events




Add Restream URL

Select the checkbox “Add Restream URL”. This URL represents the destination to which 3Play will send video with captions encoded via 608 standard, and must be in RTMP format (additional formats, such as HLS, are not supported in this workflow). For example, if you want to publish your video on Vimeo Livestream, you will copy the RTMP URL & Key provided by Vimeo Livestream and paste it into the restream URL field in 3lay). 

💡  The Restream URL should concatenate the stream URL & Key, separated by a forward slash.

For example, let’s say your stream URL is: rtmp://, and your stream key is: 12345. Your restream URL will be: rtmp://

3Play will send video with captions encoded via a 608 standard to this destination.





Click Schedule Event & Copy Input RTMP URL & Key from confirmation page

3Play will provide you with an Input RTMP URL & Key on the confirmation page. Enter this information into your encoder.




Start streaming at the 3Play event start time

The specified start time in 3Play represents the time at which 3Play will initiate a service to listen for your stream at this time. Do not attempt to stream to 3Play before the event start time, as the stream connection will fail to connect from your encoder to 3Play and your encoder will display an error message.


Video Player Compatibility

This workflow to deliver in-player captions via 608 encoding standard should work with any video player that can support an RTMP stream and that has the capability to decode 608 encoded captions. This workflow is compatible with the following video players, and may work with video players beyond this list. We recommend testing prior to any live events. 

Vimeo Livestream, AWS Medialive, Brightcove, JW Player, and Panopto


Some video players may not be able to decode 608 encoded captions, or may require advanced streaming settings. Players that are not yet compatible with in-player captions are listed below:

Uscreen, Hopin, On24


If you are using a video player that is not yet support by this workflow to deliver in-player captions, we recommend utilizing our workflow to deliver captions to the 3Play caption embed. 

Click here to learn more about Scheduling Live Captions for an RTMP Stream with captions delivered to the 3Play iFrame or Javascript Embed.



Key Notes:

Streaming recommendations: we currently have limitations on event length, related to streams with higher bitrates. Please see the below chart of event length maximum recommendations at different bitrate ranges:

<1mbps - 600+ minutes
1-2mbps - 330 minutes
2-3mbps - 220 minutes
3-4mbps - 160 minutes
4-5mbps - 135 minutes
5-6mbps - 110 minutes



In this workflow, 3Play is streaming both video and captions to the end video player - if you choose to End Event through the 3Play interface, this will also end the video stream. Do not select this unless you want to stop streaming your video. 


Additionally, if your stream to 3Play, or the 3Play stream to your specified restream URL is compromised, both captions and video will be impacted. As such we recommend that customers using this workflow have a secondary stream directly between their encoder and the end video player as a fall back.



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