could not play video file at larger window and fullscreen

I download a video ( 1 hour 44 minutes ) from youtube. It can be played correctly there in full screen.
In small window I can play it, but not in larger. There is long lags occured in video playing.
I have AMD Athlon(tm) 64 Processor 3200+, 2 GB RAM, GeForce 6600/PCIe/SSE2, 64-bit OS installed.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: libgstreamer0.10-0 0.10.36-1ubuntu2
ProcVersionSignature: Ubuntu 3.8.0-26.38-generic 3.8.13.2
Uname: Linux 3.8.0-26-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.9.2-0ubuntu8.1
Architecture: amd64
Date: Wed Jul 24 14:10:59 2013
InstallationDate: Installed on 2013-01-04 (200 days ago)
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
MarkForUpload: True
SourcePackage: gstreamer0.10
UpgradeStatus: Upgraded to raring on 2013-04-25 (89 days ago)