Open the "Design" tab of your job and click on the "Edit" button for the body of the job:
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Click the "Source Code" button on the toolbar
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Paste the embed code of your video where you would like it to appear in the job ad and click save
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Note: You can get the embed code from youtube by clicking the "Share" button in the bottom right of the video:
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Then click the "Embed" option
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Then copy the code presented eg:
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To add a video to a Seek ad, do the following:
Go to a current Seek ad and click edit:
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Scroll down to the Video Link field. The pasted link must resemble this format:
https://www.youtube.com/embed/dVDk7PXNXB8
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Click Save and Back when done, and your ad will be updated (if you have the necessary permission on Seek).