Skip to main content

HTML Guide

Bad value “” for attribute “poster” on element “video”: Must be non-empty.

An empty value for the poster attribute on a video element is not valid; the attribute must contain a non-empty URL.

The poster attribute specifies an image to show before the user plays the video. According to the HTML living standard and W3C specifications, if the poster attribute is present, it must have a non-empty value that is a valid URL to an image resource. Using poster="" is invalid and triggers validator errors.

If you do not want to show any poster image, simply omit the poster attribute altogether. If you want to show an image, provide a valid image URL as the value.

Valid examples:

Video without a poster (omit the attribute):

<video controls>
  <source src="movie.mp4" type="video/mp4">
  Your browser does not support the video tag.
</video>

Video with a poster image:

<video controls poster="thumbnail.jpg">
  <source src="movie.mp4" type="video/mp4">
  Your browser does not support the video tag.
</video>

Invalid (causes error):

<video controls poster="">
  <source src="movie.mp4" type="video/mp4">
  Your browser does not support the video tag.
</video>

Always either use a valid URL in the poster attribute or omit it entirely to ensure HTML validity.

Learn more:

Related W3C validator issues