Hi there, am in same trouble!
Doing research 5 hours per day almost a week, but nothing particular about this case, starting to be my nightmare mystery...
Check this:
By inspecting some website like kissanime I've found one that got the right URL for the video.
Example of video.
This one (THE right URL I need): h-t-t-p-s: //lh3 [dot] googleusercontent. com/mU1n-bGv_OpLYOKdGa70NRJUrdLB1-qe6gUY0iNweQ=m18
And now the same site got that covered also.
Gives this url of the video: h-t-t-p-s:// redirector[dot]googlevideo[dot]com/videoplayback?requiressl=yes&id=cf5e9529492fa23a&i tag=18&source=picasa&cmo=secure_transport=yes&ip=0 .0.0.0&ipbits=0&expire=1438675745&sparams=requires sl,id,itag,source,ip,ipbits, expire&signature= 10A966A2410A09F04020CDAF0BD14DC3510FA80B. AB6EB3364FBB6298443CA1A9FCA19100BCEE00DB&key=lh1
...which expires after some time.
Both urls give the video for watching, (h-t-t-p-s: //r2---sn-vuxbavcx-n3bl [dot]googlevideo[dot]com/videoplayback ) different url for each IP tries to watch it.
The question is how do I get the 1st URL (this one: h-t-t-p-s: //lh3[dot]googleusercontent[dot]com /mU1n-bGv_OpLYOKdGa70NRJUrdLB1-qe6gUY0iNweQ=m18)
It's more than a clear that's Picasa album, but how they got that address, so my video will never expire or so.
I need HELP!