latz

<ul>
<li>No coding required.</li>
<li>Integrates into theme customizer.</li>
<li>Individual thumbnail sizes for every installed theme.</li>
<li>Easily add and remove new sizes.</li>
</ul>

Easy Thumbnail Sizes

Nice plugin

The easiest way to add custom sized thumbnails to any installed theme. No coding required.

Kyle Gilman

<h4>A plugin to make video players, thumbnails, multiple resolutions, and video galleries.</h4>
This video plugin adds several options to any video uploaded to the WordPress Media Library. If your video can be played natively in your browser, or if you have FFMPEG installed on your server (optional), you can generate thumbnails from your video. Using either the “Generate” or “Randomize” buttons will create a selection to choose from. Click “Insert into Post” and you’ll get a shortcode in the post editor that will make a flexible, responsive video player.
If you provide multiple H.264 resolutions, Videopack can automatically select the one closest to the size of the player or a resolution of your choice, and provide a button for users to select the resolution manually. If FFMPEG is installed on your server, Videopack can encode the videos automatically.
You can also use Videopack to create a popup video gallery. The shortcode uses options similar to the <a href="https://codex.wordpress.org/Gallery_Shortcode" rel="nofollow ugc">WordPress image gallery shortcode</a>. In its simplest form it will create a gallery of all videos attached to the post.
You can now add advertisements to your videos using the <a href="https://www.videopack.video/add-ons/videopack-ads/" rel="nofollow ugc">Videopack Ads</a> premium add-on which you can purchase from the Add-ons tab of the Videopack Settings page or on the <a href="https://www.videopack.video/add-ons/videopack-ads/" rel="nofollow ugc">Videopack website</a>.
Not compatible with the Block Editor. Please continue to use the <a href="https://wordpress.org/plugins/classic-editor/" rel="ugc">Classic Editor</a>.
Visit the <a href="https://www.videopack.video/docs/" rel="nofollow ugc">Videopack Documentation pages</a> for more info.

Videopack

Great solution for generating thumbnails from images. 
Thank you for the work put into this plugin.

Excellent

Makes video thumbnails, allows resolution switching, and embeds responsive self-hosted videos and galleries.

Easy Thumbnail Sizes vs Videopack