Hands-On Video: Create Closed Captions in Gemini

Chris Holway, a Product Manager with the Gemini team, walks you through these easy-to-follow steps, so that you can create closed captions for your videos in the Gemini UI.

Steps to Create Video Closed Captions

Captions appear as an overlay to the video asset in the muted state and will disappear in the un-muted state. You can add a caption file to youe videos via the Gemini UI, API and Bulk.

Gemini simply sends the video + caption file in all ad responses. The supply endpoint will play the caption file if it can and, if not, it will play the video without captions (i.e., the status quo).

Follow these steps:

  1. Create a new ad, entitled Wonder Woman, from the Ads & keywords menu and choose the ad format as Video.

select ad format

The panel for the Video ad appears.

create a new ad
  1. In the Ad details panel, under Upload Video, drag and drop the video that you’ve created into the Video pane from your desktop, in this case, Wonder Woman.mov.

upload the video
  1. While the video is loading, you can upload the Large rectangle image (which is required) into the image pane. The Square image will populate automatically. Ensure that these images are 1200x627 pixels and 627x627 pixels, respectively, according to image specification requirements.
  1. Select and open your Wonderwoman.srt caption file on your desktop, which includes your captions for the images and follows the defined specs for each image (shown below in the section on supported file types), drag and drop the Wonderwoman.srt caption file on the blank video screen.

drag drop file
  1. Click the view caption item at the bottom of the video.
  2. Enter the text for the Ad title and Ad description, along with your Company name and the Destination URL.
  3. In the Call-to-action button, enter in this case: Watch Now.
  4. Pause the video, save the ad and you’re good to go.

What File Types are Supported?

Gemini native closed captioning provides support for industry-standard file types, including:

  • .srt
  • .vtt


For its initial release, the .ttml file format is not supported.

A .srt caption file should contain the following elements:

  • A numeric counter identifying each sequential subtitle, in this format: (hours:minutes:seconds,milliseconds).
  • The time specified that the subtitle should appear on the screen, followed by this indicator: –> and the time it should disappear.
  • Subtitle text itself on one or more lines.
  • A blank line that contains no text, indicating the end of this subtitle.

For example:


00:00:05,000 –> 00:00:08,400

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00:00:09,600 –> 00:00:11,800

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Learn More

For more information, check out Use Native Video Captions For Maximum Recall of Ad Messaging.