Server 2012 R2 T10 Thin Client video playback performance

I'm a tech for a school and I just upgraded all our 2008 R2 servers to 2012 R2. We use a mix of WYSE T10 thin clients and desktop pc's. When playing back a video on a thin client from say youtube (teachers love youtube) if it's in the default small window it plays back perfectly. Smooth video and sound. Full screen it and it becomes a choppy mess. On desktop pc's over rdp it plays perfectly full screened.

It does not do this on Server 2008 R2. I still have one old 2008 R2 server I did a P2V conversion on that full screen video plays back fine on a thin client. This VM has very little resources yet it plays fine.

I upgraded our thin client firmware from 7 something to 8.0_512 and it runs better (sound doesn't skip so badly) but it's still pretty bad. What can I do to fix this?

We have gigabit per port switches and Dell PowerEdge R620 servers with 64GB ram. It's not a hardware issue.

School has now started and teachers are not very happy..I spent all summer on this and am at my wits end.. Thanks for any help!

Here is my config:

;*************************************************************
;*                          General 1                        *
;*************************************************************

Privilege=High
Fileserver=10.0.10.27
ScreenSaver=0 Type=0
DesktopColorDepth=32
Desktop=wysetca.jpg

;*************************************************************
;*                         Peripherals                        *
;*************************************************************

Language=Us
DefaultPrinter=LPT1
Printer=LPT1 Name="HP LaserJet 1200" PrinterID="HP LaserJet 1200" enabled=yes
ThinPrintEnable=yes Port=4000

;*************************************************************
;*                             Time                          *
;*************************************************************

Timeserver=10.0.10.18 Timeformat="12-hour format" Dateformat=mm/dd/yyyy
TimeZone="GMT - 06:00" ManualOverride=yes Daylight=yes Start=030207 End=110107

;*************************************************************
;*                           Network                         *
;*************************************************************

Autoload=2
SignOn=No
MaxVNCD=1
VncPassword="***"
VncPrompt=No Accept=5 ActiveVisible=yes

;*************************************************************
;*                             RDP                           *
;*************************************************************

SessionConfig=RDP EnableVOR=no MapDisks=yes

;-------------------------------------------------------------
;-                        RDP Session 1                      -
;-         Each line but the last must end with a  '\'       -
;-------------------------------------------------------------

CONNECT=RDP \
Host=tsfarm.tc.local \
Description="Teachers" \
Colors=true \
Fullscreen=yes \
Domainname=tc.local \
Sound=local \
LocalCopy=yes \

;-------------------------------------------------------------
;-                        RDP Session 2                      -
;-         Each line but the last must end with a  '\'       -
;-------------------------------------------------------------

CONNECT=RDP \
Host="studentts.tc.local" \
Description="Students" \
Colors=true \
Fullscreen=yes \
Domainname=tc.local \
Sound=local \
LocalCopy=yes \

;-------------------------------------------------------------
;-                        RDP Session 3                      -
;-         Each line but the last must end with a  '\'       -
;-------------------------------------------------------------

CONNECT=RDP \
Host="admints.tc.local" \
Description="Administration" \
Colors=true \
Fullscreen=yes \
Domainname=tc.local \
Sound=local \
LocalCopy=yes \