Is there a way to reference a thumbnail from an existing video uploaded to Vimeo? Right now, I am creating them from hand. Thanks!

If you right click on the Vimeo thumbnail (within the video's settings) and select save as picture, the file requester will reveal the 9 digits you need to plug in to your RSS feed to use the existing thumbnail.

For those using Vimeo Pro I noticed that if you follow what the previous poster said, click the video Settings, then right click the thumbnail of the video in the top left, you right click > Copy Image location. It will give you something like:

https://i.vimeocdn.com/video/607010945_300x170.jpg

Change the 300x170.jpg ending to 800x450.jpg and it'll resize, viola!

https://i.vimeocdn.com/video/607010945_800x450.jpg

I actually had old SD content which Roku gave an error "Thumbnails must be 16x9 aspect ratio".  After resizing them in Photoshop on a whim I took the SD url, and again typed in ending it "800x450.jpg" and sure enough it resized it accordingly. Their servers must do the image sizing on their backend. Saves a ton of time. Just paying it forward in case anyone else is using them going forward and didn't know about this trick.

I've been having a nightmare day trying to get my thumbnail to appear on my Roku Channel. Instead, I'm getting color bars

I can't figure out for the life of me what the problem is. Here's the line from JSON Feed:

      "thumbnail": "https://i.vimeocdn.com/video/742943172.jpg?r=pad",

When I plug in the URL and stop at jpg, it works...when I paste the whole thing, I get color bars.

Any ideas?

Try changing the URL to something like this:

"https://i.vimeocdn.com/video/742943172_800x450.jpg?r=pad"

The "800x450" is the desired image size. You can pretty much use anything that you want, but I think Direct Publisher prefers 800x450.

The "?r=pad" is optional. If present it will pad the image on the left+right or top+bottom with black bars instead of cropping to fit the specified size.