Does Photos App really upload the original images or videos to iCloud Photos Library?

[Pannha]

I decided to turn on the iCloud Photos Library on both OS X and iOS. I have 8.9 GB of Images and videos, but after all of items were uploaded, I noticed it's only 7.8 GB were uploaded. Did iCloud Photos Library decrease my image quality or video resolution? In addition, I accidentally uploaded the same videos on youtube, and the videos that uploaded by OS X (which is the device that store my original videos) is up to 1080p, but another video uploaded by iOS (video automatically downloaded from iCloud photos library) is only 720p.

 

[Just_Me_D]

From what I can tell, the originals pics I've taken seemed to be uploaded without any degradation in quality or size.