Q:

GPU accelerated Video decoding on a browser.  Is it possible? 

Let's say I have a Rpi (B+) and want it to act as Kiosk, where a video will play on a loop in fullscreen.  The video will change programatically, so I need an API to control it.  I've done this before, in x86 machines, with no problem, in a web based application (Javascript and HTML5).  
The problem I'm having is that NO browser is (apparently) using the GPU to decode the video. 
Event their Web Browser that should support "Hardware-accelerated video decoding" can't play videos.  I just installed Raspbian (NOOBS) and the browser should at least play the same video as they do on the video. 
Omxplayer runs it well, but flickers when it loops and shows some text ("Seek ..."). 
As this would be a project that will involve around 400 Raspberry PI (if it can do what I need) on different locations, I really need a solid solution. 
Is there a way have a looping video, gpu accelerated, on a browser on RPi? 
EDIT:
I tried embedded mp4/h.264 videos with a regular  tag.  Every browser fails to play the video.  Epiphany and Chromium only show a black "area" and the controls.  No video.  Midori gets some frames, but the cpu tops.  Youtube/Vimeo also fails to play. 
EDIT 2:
After I did a fresh install and set the GPU memory to 128MB instead of the default 64MB I managed to play a video, smoothly, on Epiphany.  The CPU didn't reach 100% (70%-95%).  Although, when I tried a full hd video, the performance dropped severely (< 1 FPS) but the CPU was only at 50%, the bottleneck was probably the memory.  I'll pick a RPI2 and test it.  

A:

Yes, it is possible, I started this project some time ago but I had to stop because of insufficient time.  
This is the best result I could get (1080p): https://youtu.be/fVM1GRDhXGw.  It is based on this open library: https://github.com/carlonluca/pi.  Some more info  here.  
The demo uses that library with WebKit1 in QtWebKit, all running without X11.  It seems much more difficult to do it with WebKit2.  Unfortunately the quality was not perfect, I don't know if it is possible to improve it.  However I don't see why using a browser in the first place if the desire is just to play a fullscreen video. 
Note that I'm the author of the project, so I'm reporting it just because I know it.  There may be a million other approaches.