Is it possible to generate a thumbnail for a YouTube video? Yes! It’s useful to display thumbnails with links in sidebars, or to replace the YouTube embed code with a video within your RSS feed or email. This is already a feature of some email platforms, like WordPress Newsletter Plugin. Attempting to write your own YouTube thumbnail generator could be quite a task.
The good news is that you don’t have to generate a thumbnail, YouTube has several waiting for you.
Here’s a video URL – notice the video id?
Here are the images in a couple sizes and frames, note the video id is embedded in the URL:
An easy way to embed the thumbnails in your sidebar would be to enter the image URL manually as a custom field, then customize your theme to display the custom field if it exists.