I think browsers are becoming more strict regarding what content will be shown on a page initially loaded over https – this is the browser’s content security policy, and the only way to overcome this is to embed external content from other domains via https on https pages.
Here’s their advice for overcoming the issue: https://developers.google.com/web/fundamentals/security/prevent-mixed-content/fixing-mixed-content
So if the youku site supports https, you should use that embed code. If not, you could optionally force those pages to be loaded over http so that ‘mixed’ content is not an issue. If the .html page which contains your embeds is loaded over http, there would be no issue. (It looks like your site forces https, which in my opinion is a good thing)