Adding WebVTT Captions to VOD

This article explains how to add caption files to videos and outlines the full workflow for managing captions in IBM Video Streaming.

How to Add Captions

1. Hover over the video.
2. Click the down arrow icon next to the video date to open the menu.
3. Select Edit.
4. Go to the Captions tab.
5. Click Add Captions.
6. Select the language.
7. Choose the .vtt file to upload.
8. Click Upload.

There are over 180 supported languages (including variations such as English UK and English US).

Uploaded captions will be processed after submission. This may take several minutes. You will receive an email notification once processing is complete.

Note: Ensure your caption file is correctly formatted before uploading. Failed uploads usually indicate invalid captions.

Auto-Generated and Live Captions

Auto-generated captions can be edited directly in the dashboard.

If your video includes live embedded (608/708) captions, you will see “English (live)” listed. These captions are automatically converted into standard .vtt format and function like uploaded captions.

Closed Captions List

Uploaded captions are displayed in alphabetical order under the Closed Captions tab.

Status

Captions can have three different statuses:

• Processing: Immediately after upload; may take several minutes.
• Published: Automatically available once processing is complete.
• Unpublished: Hidden from viewers until re-enabled.

Default Captions

Only one caption file can be set as the default. You can update this setting from the caption settings menu.

Options

Hover over a caption file to access available actions:

• Download: Retrieve the processed WebVTT file.
• Publish/Unpublish: Toggle visibility for viewers.
• Settings: Modify language or set as default.

Possible Issues with Caption Files

File Format

WebVTT is the standard format for displaying timed text with HTML5 video.

If you upload an unsupported format (such as .srt), you may see the error:

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

Convert your file to .vtt before uploading. DFXP files are also supported.

Formatting

Only basic formatting is supported, including:

• <b> (bold)
• <i> (italic)
• <u> (underline)

Other formatting will be ignored.

Encoding

Caption files must use UTF-8 encoding. If not, you may encounter this error:

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

File Size

Maximum supported file size is 1MB.

Trimmed Videos

VTT timestamps must match the original video timeline, not a trimmed version.

Upload Failures

If your upload fails, validate your file using a tool such as: WebVTT Validator.

Playback Limitation

*Playback of uploaded captions is not supported on Windows 7 using Internet Explorer.*

Caption Limits

Up to 11 VTT caption files are supported per video. Uploading more may cause playback issues.

Closed Captions and Live Playlists

Live Playlist uses VOD content as its source. Videos with multiple captions will carry those captions into playlists accordingly.

For more information, see: Using Live Playlists to schedule video playback