Action Details
Requirements and how-to articles for Twitch's action:

Requirements
You need this to get it done:

Left Unit
Dimensions: 450 x 350 pixels
Maximum file size: 150K
File format: .jpg/.png along with layered template .psd
Animation: No
Third part tracking: Impression 1x1 and click tracker site served. No DMP 3rd party JavaScript tracking.
SSL Compliance
Twitch does not allow the use of any unapproved third party ad technologies. Twitch requires all ads and third party vendors to be SSL-compliant. All components of video and display ads including creative and tracking must be provided as and able to serve via SSL (HTTPS).
Right Unit
Dimensions: 450 x 350 pixels
Maximum file size: 150K
File format: .jpg/.png along with layered template .psd
Animation: No
Third part tracking: Impression 1x1 and click tracker site served. No DMP 3rd party JavaScript tracking.
Hex Colour Code
Can be included in file name, or sampled from units/designed template.
Requirements missing or found errors? Report

How-To Articles
A list of useful links for you:

0
Twitch Advertising - Homepage Headliner
The official help article from Twitch listing all details of the Homepage Headliner.
Official
Link missing here or found errors? Improve How-Tos