See ADA Guidelines for further clarification. 

Implementation Vendor
Text & icon elements maintain a color contrast ratio of 4:5:1 and images must have a color contrast ratio of 3:0:1
Ensure all custom buttons and elements are given the appropriate aria role and label / alt text
Ensure all custom buttons and elements have the correct tab index and receive keyboard focus if needed 
Avoid using CSS background images except on buttons
Hide content in code from all users that should be
Implement audio description files
Ensure first node is muted if autoplay
Custom eko shell buttons have proper alt text

 

Production Partner
Text & icon elements maintain a color contrast ratio of 4:5:1 and images must have a color contrast ratio of 3:0:1
All visible elements in eko studio are named and ordered appropriately 
All non-interactive eko studio elements are categorized as Graphic Only
Avoid using CSS background images except on buttons
Provide closed captions
Provide audio description srt files