What is a WebVTT (VTT) file?
WebVTT files, also known simply as VTT files, are a web standard closed captioning format and are often a required element for certain delivery destinations. They use the file extension “.vtt”. Based on a syntax structure similar to the SRT (SubRip) subtitle file format, VTT’s are human readable and can be opened using any simple text editor for review. Where SRT files are intended for use as subtitles only, VTT files can contain information that allows them to be used for closed captioning.
What are the differences between SRT and VTT?
VTT and SRT files look similar, however there are a few key differences, and so they are not interchangeable. An SRT cannot just have its extension changed to convert it into a VTT. The key differences are:
- WebVTT files use a unique header as the first line of text.
- WebVTT files support user/developer comments.
- SRT files require that each caption includes a sequence number. WebVTT files support SRT sequences numbers, but they are not required for the file to function properly.
- SRT files differentiate fractional timecode values (milliseconds) with a comma [,]. WebVTT files differentiate fractional timecode values using a period [.].
- WebVTT supports more diverse formatting tags and values, including positional information.
- WebVTT does not support extended characters. Extended characters must be represented by UTF-8.
| SAMPLE SRT | SAMPLE WEBVTT |
|---|---|
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VTT’s and dotstudioPRO
Since WebVTT is a newer closed captions format, many clients may not have files readily available for delivery. Each destination platform has its own closed captions specifications; while some require SRT files, others will need VTT’s. It is strongly recommended that each video uploaded to dotstudioPRO includes both an SRT file and a VTT file. For dotstudioPRO Aggregation deliveries, both SRT and VTT are required.
dotstudioPRO is capable of generating VTT files from user provided SRT’s. If you or your clients are only able to provide SRT files, the below dashboard features may be helpful.
How To: Generate a Single VTT File in DSP
If you need to generate a VTT file for a single title or collection of titles you can do so using the captions settings for those individual videos. A title’s captions settings can be accessed through the EDIT button beside any video on your dashboard.
Before a VTT file can be generated, a video will need to have an SRT file associated with it. If no SRT is uploaded, you can do so by selecting a language from the language dropdown menu, then clicking the SELECT FILES button to upload a file from your computer.
Once an SRT is associated with a video, it will be listed under the Caption Files heading. A VTT can be generated by clicking the GENERATE VTT button beside any uploaded SRT. A warning will appear. Clicking the button will prompt a warning, asking you if you’d like to proceed. After clicking “YES” a VTT file will be generated and added to the list of captions using the same language value as its parent SRT.
Warning: dotstudioPRO supports one SRT file and one VTT file for each language. Clicking the GENERATE VTT button when a VTT already exists in the source SRT language will overwrite the original VTT with the newly generated one.
How To: Enable VTT Auto Generation in DSP
It is possible to set a dashboard so that VTT’s are automatically generated whenever an SRT file is ingested. Doing so will mean that every time a user uploads or delivers an SRT file to the dashboard a corresponding VTT file will be generated and overwrite any old VTT file in the corresponding language.
This setting is ideal for dashboards where VTT’s will rarely ever be uploaded directly, and where the formatting and timing of the SRT and VTT will always be mirrored. This setting is not ideal for syndicated dashboards, dashboards supporting multiple contributors, or dashboards where VTT’s supporting complex formatting could be supplied by a user.
To enable VTT Auto Generation, first click the USER ICON, then under SETTINGS select COMPANY. From the company options, click on the CLOSED CAPTIONS submenu. Here you can enable or disable VTT Autogeneration.
When VTT Autogeneration is enabled:
- A new VTT file will be generated whenever an SRT is ingested to the dashboard
- Whenever a new VTT file is generated, it will overwrite any existing VTT associated with the same video file in the same language.
- The Generate VTT button and Upload functions for VTT’s will still function as normal
- A warning will appear on the Captions Settings for all videos to remind users that this feature is enabled.
| AUTOGENERATION ENABLED | AUTOGENERATION DISABLED |
|---|---|
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How To: Spotcheck VTT Playback
Our video player supports the display of WebVTT closed captions. To spotcheck the timing of your VTT files, open the EMBED settings and click the PREVIEW button. Doing so will open a new tab in your browser, where you can view your video file and any VTT closed captions files associated with that video. This can be used to spotcheck your captions for sync and formatting.
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