The following is what I found on YouTube and wanted to share it with you here. The channel art on YouTube is not just a small image, but one that you should look at exploring a bit further if you are using your channel for professional reasons.
I thought I might post it in it’s entirety for educational reasons in case you were not aware.
I think it is a vast improvement over the latest on twitter which conflicts with text.

Channel Art Guidelines
Channel Art Specs
For optimal results on all devices we recommend uploading a single 2560 X 1440 px image that has been optimized to fit the below template:
You can download the template here: Channel Art Template (Fireworks) Channel Art Template (Photoshop)
How it works on Desktop
The below slice would be your desktop banner. It’s total dimensions are 2560 X 423 px.
New channels will have a flexible width on desktop, meaning that the site will scale to reveal more content on larger browser windows. There is a minimum size at which point the site would no longer adapt and a scroll bar would appear in the browser window. At the minimum width the channel art is 1546 X 423 px (this is the “Safe area” given that text & logos will not be cut off). At the maximum width, the channel art is 2560 X 423 px. This means that the “SAFE AREA” (channel art at minimum width) will always be visible and the areas to the right and left (shown with green arrows) might be visible depending on the viewer’s browser size.
Example of channel at Min width:
Example of channel at Max width:
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