Understanding Closed Captioning Formats: What You Need For Your Player

By: Aylin Dunham



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With so many different caption file formats, it can be difficult to know which ones you need for your video to display closed captioning. Verbit offers a list of captioning formats, but you need to know where your video will play in order to choose from this list. This depends mainly on the platform or player you intend to use.

When you play a video, the player will read the caption file if it supports closed captioning. However, each player or platform has different file requirements for displaying captions. Most web media requires caption data in a “side-car” file, meaning captions are in a separate file from the video. All players have slightly different settings when it comes to making caption files work.

Rather than give you a long list of formats, we’ve picked several popular platforms and players to let you know which formats they accept.


For YouTube, you’ll likely need an .SRT File. Verbit can send this file directly to your YouTube account when you submit the URL to your YouTube video on our platform.


You can also add caption files to Vimeo during the video file upload or at any time. Vimeo accepts .SRT files, as well as WebVTT.

Ensemble Video

Ensemble Video integrates with Verbit, which automatically makes the correct output format available. You are also able to upload your own caption files by requesting an .ensemble.xml caption file. These files are variants of the DFXP caption file format.

TechSmith Camtasia

For accessible, searchable and compliant videos in Camtasia from Techsmith, you will need an .smi or .srt caption.


For quick captioning with Blackboard Collaborate, you can submit a list of Collaborate archive URLs. With those files, Verbit will generate captions for you and encode them into the video file in M4V/MP4 video format. This format will allow you to view captions on any computer or mobile device with iTunes or Quicktime.

JW Player

For JW Player, you will generally need a .DFXP, .SRT, or .VTT file.


You can show caption files in Flowplayer as an external text file or embed them inside an mp4 container. Using Verbit’s Video Encoding, you can also create subtitled videos.

Windows Media Player

Generally, you use .SMI files with Windows Media Player, but there are four different methods of implementing them.

QuickTime Player

There are several ways to associate captions with your Quick Time videos. The recommended file type is .QT.XML.


For Captions with RealPlayer, add .rt.smil and .rt caption files. Just place them in the same directory as your media file.

Software Packages (iSubtitle, Handbrake, DivX, PS3, VLC, and MPlayer)

Software packages, including open-source and freeware packages for captioning and subtitling, often require a .ASS file, also known as the Advanced SubStation Alpha format. 

Adding closed captions to your videos improves their accessibility and helps them reach larger audiences. Fortunately, adding captions is easy with an experienced accessibility partner. If you have any questions about adding caption files to your videos, please contact Verbit.