"As most of you know , SP2013 Newsfeed provides a cool feature wherin you get a Video thumbnail and an embedded player for links that you post from youtube. In most of the cases it works, but in some cases wherein you use a proxy server, this functionality doesn’t work. I tried to look at documentation on technet, but as usual nothing.
So there are 2 stages to resolve this issues
- Application Pool account needs access to the Internet
Login to the WFE’s servers on your SP2013 Farm and then put in the proxy information, so that the account is able to access the internet. Test it by visiting, https://youtube.com. Repeat this step on all WFE’s. This resolves part of the error and you are now able to connect to gdata.youtube.com to get thumnail information and SP Attachement class is now able to build the complete JSON object. However, the video thumbnail will still not work because the SP Farm needs to trust the website using the *.google.com certificate
- Enable Trust between SPFarm and Youtube.
On one of the WFE server, visit https://youtube.com and on the IE Browser, click on the lock icon in the address bar and download the certification(by clicking on details–>Copy to File, accept the defaults and store it on the local computer of your WFE server with yourfilename.cer).
Once you have this cert go to Central Administration–>Security–>Manage Trust, click new, give it some name and browse to the cer file you just downloaded and click OK.
Once this is done, go to you cer file on your local computer, double click it, Install Certificate and just follow the default prompt, the import will add the Certificate in your trusted root. Make sure to use Local Computer and not local user.
Repeat Step 1 and 2 on all of your WFE servers in the SP Farm.
Go back to your site and now the video embedded URL’s should be working"
Copied from the link shared by user 34659. It was wrong to just post a link, but it was indeed the solution for the problem.