Captioning Compendium Part I: The Basics

Updated: Feb 27, 2023

A TV and a tablet both with a closed captioned video

Who knew there was so much technology behind that series of subtitles on your screen? Actually, closed captioning isn’t that complicated, but let’s take a moment to differentiate between the two types of captions you generally see on the screen.  

For pre-recorded content, pop-on captions are most common. They are displayed all at one time, and disappear when that particular piece of audio in the program is complete. New captions appear on the screen when the program has more audio that requires transcription.

In contrast, roll-up captions are most popular for live content. New captions are appear on the lowest line of the screen (there are usually two or three lines) and then “roll up” to replace the line above it – and make room for new captions as they appear.

Online captioning is the term used to describe the captioning of live content, typically as it happens. From news to meetings, captions are generated in real time.

In Cablecast, the online captioning process is very smooth. You simply enable live captioning with one click in the schedule run. Behind the scenes, live content is routed into your Cablecast VIO or Flex video server as usual, but the audio is sent to Cablecast’s cloud-based captioning engine for speech-to-text analysis. When the text data is sent back, your server acts as a live caption encoder, adding captions to the SDI signal before it is delivered to your cable company or live stream. Cablecast’s online captions are two-line roll-ups.

Offline captioning is used for pre-recorded content. Cablecast makes this type of captioning a one-click process through the show record. When you enable captions, the system will create sidecar files of captioned content that live on your video server and will run automatically when your content plays. (watch: more about caption sidecar files in under a minute) Plus, any VOD content linked to that show record will get updated caption files in WebVTT, a common format for caption on the web, with no transcoding. Cablecast’s offline captions are pop-on format.

Want to learn more? Get in touch for easy and accurate caption solutions from Cablecast.

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