It looks like the Youtube/Dailymotion/Vimeo integration (Haven't tested other, but I think the same bug will happen) doesn't work. Instead of the player, I get the code from the editor :
http://i.imgur.com/yV81WXk.jpg

About the images :

Not sure it's a bug. Check this :
http://i.imgur.com/BDPxVEl.jpg

I'd like to know what's the "Source of the image" is supposed to do. If I choose the small format, the thumbnail is the 320 x 180 enlarged to 1280 x 720. It makes the picture pixellised :
http://i.imgur.com/urPrKQJ.jpg

I don't think it's supposed to do that. Is there a problem? Or is it intended?

Another problem with the images. Previously, when you chose a picture, the media manager would bring you back on the same folder the next time you open it. But now, it brings you on pics uploaded on the article, no matter where you were previously. It makes the time to select a new picture way longer :/

Here is an example : https://www.youtube.com/watch?v=oCAC2HvI9wE

This issue already solved in 5.1.6 but it will not solve your existing blog post content, can you provide us with your PHPMYADMIN and FTP access so we can run some php script to help you update all of your existing blog post convert to video on blog page?

Nope, actually that is not a bug, if you select "small image source" and you also set that image width/height to 1280x720px, it will display this size of image width/height in blog content.

The screenshot I took comes from an article done after the update to the 5.1.6. Here is another screenshot. I took it minutes ago, coming from a preview:
http://i.imgur.com/IY2oXoZ.jpg

I updated the original post with the ftp access

Hmmm... I don't understand the purpose of those 2 fields. Is it to adjust the size of a pic after choosing the thumbnail used? In that case, the problem is they don't keep the ratio like the previous media manager did.

Can you try again and see is it work fine now?

Yes, that 2 fields is allow user to adjust the image size.
Based on what you explain, it sound like that is true, if you change that image source from the image, it should automatically reset that width and height value same with what you select the image source, I will discuss with the team regarding this.

Still not working : http://i.imgur.com/wieADwR.jpg

Yes, that 2 fields is allow user to adjust the image size.
Based on what you explain, it sound like that is true, if you change that image source from the image, it should automatically reset that width and height value same with what you select the image source, I will discuss with the team regarding this.

Can i have this post URL?

Oh, you are referring the preview section, yes, that is bug, by right it should show the embed video on the preview as well.

I will log this issue into our tracker as well.