Adding VTT closed caption files to videos

Adding WebVTT captions to VOD

This article covers the interface for adding caption files to videos as well as the workflow involved.

To get started with captions choose the “Closed Captions” button on the dashboard. If you have never uploaded a .vtt caption file before, this tab will be empty. Click “Add captions" to upload your first caption file.

Note: Please ensure that your caption file has been correctly edited before uploading, as currently only IBM Video Streaming Auto Generated Captions can be edited in the Dashboard. 


In case your video has live embedded (608/708) captions you will already see “English (live)” as the first element of the caption list. These live captions have been processed and converted into standard (.vtt) file so they will function just like any other uploaded captions.


Upload Tab

  1. As a first step, you will select from a predetermined list of languages from a dropdown menu. You will find 180+ different languages and some variations of them (e.g. English UK, English US).

    Note: If you have previously uploaded captions in the selected language new captions are going to overwrite them.

  2. Click on the “choose file” button that will let you select a file from your computer. Choose the .vtt file you want to upload. Currently, the platform only allows .vtt files to be uploaded as captions. Read more on this topic below

  3. You can set these captions to appear on the player by default. In this case they will be displayed immediately as soon as playback starts without any additional settings.

  4. Uploaded captions will need to be processed. This process might take a while. When they are ready, we will send a notification to the email address you provided. This input field contains the email address you used the last time. Feel free to change it. If you don’t edit it at all, it will contain the channel owner's email.

When all the necessary settings have been made click “Upload”. You will see your first captions being processed.

Closed Captions list

Uploaded captions are sorted in alphabetical order under the Closed Captions tab. Each captions are characterized by the following features


Captions can have 3 different types of status:

  • Processing: Right after uploading, processing captions can take several minutes.

  • Published: Processed captions will be automatically published.

  • Unpublished: If you want to disable one of your captions you can unpublish them. They will be no longer available for your viewers.


Only one set of captions can be set as default. You can replace the default captions with another one in the captions settings.


See what you can do with uploaded captions by hovering your mouse over it.

  • Download: You can download the processed WebVTT file.

  • Publish/Unpublish: You can decide whether captions are visible or not for viewers by changing their status

  • Settings: Change the language that was originally set up when uploading, or set these captions as default.

Possible issues with caption files

File format

Web Video Text Tracks is a standard for displaying timed text in connection with the HTML5 element. You might have captions in a different format e.g.Web SRT (.srt). In this case you’ll get the following error message.

“This file format is not supported. Please upload a WebVTT (.vtt) file.“

All you need to do is converting your caption file into a WebVTT format to be able to upload it. DFXP file formats are also supported for uploading caption files. Please contact us if you would like us to support any other closed caption file format.


NOTE:  The team is currently investigating issues with uploaded SMI captions.  After reports of issues with uploading captions in SMI format, we have removed support for captions uploaded as SMI files.  It is advisable to convert SMI caption files to WebVTT when uploading captions.  We will update this article once our team confirms that SMI captions are once again a supported caption format for upload. 


The text file you want to upload might contain special formatting. The player only supports positioning and basic formatting such as <b>, <i>, <u>. Formatting info other than this will be omitted.


UTF-8 is a character encoding capable of encoding all possible characters.  Lack of character encoding information spoil the readability of displayed text, and it may mean that your data cannot be found by a search engine, or reliably processed by machines in a number of other ways. So when you get the following error message:

“Please change the encoding of this file to UTF-8 to improve display accuracy.”

File size

There is currently a 1MB maximum file size. If your upload is failing, please make sure that your .vtt file is a maximum of 1Mb.

Trimmed Videos
VTT Timestamps are always pointing to the original video. The VTT always should be uploaded for original video timestamps.

Upload Failed
There may be an issue with the format of the caption file, we recommend that you run your captions through a validator to find the potential issues. (Ex.

Internal Error

*Please note:Playback of uploaded caption are not supported under windows 7 - Internet Explorer*

Please reach out to support if you are having issues. You can file a ticket at

Count of uploaded caption files

Currently, we support up to 11 VTT caption files for each VOD safely; uploading more than 11 could lead to issues on the player side. If you intend to use more than 11 Web VTT files on a single VOD, please reach out to our Customer Support team to investigate the opportunites.

Closed Captions and Live Playlists

As Live Playlist feature uses the VODs as source, videos with multiple captions will appear accordingly:






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