The Top Three Live Caption Encoder Workflows

Portions of this article originally appeared in The Complete Caption Encoder Guide; check it out to get the full scoop on live captioning encoders! 

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How Encoders Work
Telco Encoders
Telnet Encoders
iCap Encoders


Encoders let a broadcaster simultaneously receive and encode live closed captions via Line 21 data, allowing them to be displayed alongside a television program or video in real time. Our Rocket system allows captioners to send their caption data to Captionmax; Rocket receives the data and redistributes the captions to our clients’ encoders however is necessary. While there’s emerging virtual and alternative encoding methods, in this article, we’ll focus on the top three traditional encoder connections used in live captioning workflows: telco (analog/modem), telnet (digital/IP), and iCap (only if the encoder is manufactured by EEG).  


How Encoders Work 

Before we dive in, let’s review how caption encoding technology works. Most encoders function similarly: 

1: The caption provider transmits their caption data to the encoder.

2: The encoder collects the caption feed for transmission to the viewer.  

3: The encoder pairs the captions to the video on a specific data transmission line, known as line 21– this is the data that televisions are mandated to decode captions from.  

At Captionmax, our Rocket system has the ability to connect to all types of encoders. There are several ways an encoder may be configured to receive the caption data, and often there are multiple options available on a single device. The next few paragraphs will explain the differences between the connection options, and each workflow will have its own purpose for why to choose one over another. You will need to refer to the manufacturer’s guidelines on how to set up your encoder with the most effective settings for your workflow. Our expert live captioning technicians are always available to ensure your encoder connection process is as smooth and efficient as possible.

#1 – Telco Encoders  

While based on older analog technology, many clients still stand by dial-up telco encoders. A telco encoder requires phone lines to connect to. Our Rocket System uses dial-out modem cards to connect our writers through Rocket to the encoder’s modem. Just like your old dial-up internet, it is all possible thanks to that old familiar sound of dying robots. The screeching, clicking, and buzzing is actually the two modems discussing how to best communicate. Our dial-out modems are capable of a wide range of settings so that we can best work with each encoder. For optimal setup, our technicians will need the phone number to dial in order to connect with the encoder’s modem. To get an audio feed and follow along with what is being spoken, the caption writer will need a designated audio source to listen to. Broadcasters can route the audio through an audio coupler for the captioner to dial with their phone, or they can provide an internet-based solution such as a web conferencing platform or low-latency stream for the audio.

The information we need typically looks like this –  

Encoder: 555-500-4280  

Audio coupler: 555-500-4281  

We input the encoder’s information into our Rocket system prior to connecting and testing, so getting this set and tested in advance is extremely helpful.  

#2 – Telnet Encoders  

A telnet encoder uses an IP and port number to receive the caption data. Like a telco encoder, we also need a separate audio line to hear the dialog we are meant to be captioning. While connections are now almost instantaneous (no more whirring modems!), this does require extra checks and tests as different network security protocols can block incoming or outgoing caption data. This step is made much easier if you whitelist Captionmax before the event. A bonus to this type of encoder is that phone lines don’t need to be run into the encoder; an internet connection (ethernet) is typically required.  

The information we need typically looks like this –  

Encoder: 12.34.567.901

Port: 23  

Audio coupler: 555-500-4281  

We input the IP and port into the Rocket system and can test almost immediately. Because our caption data comes from one particular IP, it may need to be whitelisted on a client’s network for us to connect to their encoder.  

#3 – iCap Encoders  

An iCap-enabled encoder is manufactured by EEG, and with their direction, you can set up the encoder to feed both audio and video to our captioner, making it easier to monitor and caption effectively. These EEG-manufactured encoders have iCap software for improved functionality, such as sending audio to the captioner, but can also be set up as IP connections if desired. The video and audio are converted to a data stream on the iCap cloud which is accessible via an Access Code. Captions are routed through the cloud and into the encoder where it is married to the stream and ready for broadcast. These encoders can be bought or rented for any type of event or broadcast.  

The information we need typically looks like this –  

Access Code: TV2022

Once the code is created on the iCap cloud, you provide Captionmax with agency access, and we’ll be able to listen to your audio and send you the live caption data!


Encoders can seem complex, but they’re designed to simplify how quality captions are delivered to your broadcast. Whether you’re utilizing telco, telnet, or iCap encoders, you can rest assured that our captioners can deliver accessible closed captions to your media via any of these connections, allowing your message to be understood by all. 

Interested in learning more?