Old Youtube embedded codes broken after update to 3.9.2.

Hi there,

After each update of WordPress embedded Youtube videos aren’t showing up in all my posts containing old Youtube embed codes. The code is there in the html-editor but not showing up in the post. Does anybody please know
how can I solve this issue without having to replace the old code by an iframe code in many old posts? Thanks a lot for your help with this!

Regards,
Caspar