problems when playing matroska with VLC from DVD medias

[Ron Wolpa]

I am used to download videos and burn them into 8,5 Gigabyte double layer DVD medias.
Every downloaded file is tested and if it is not in perfect condition I delete it.
With .avi standard I have never had any trouble but tend not to like .mkv as it presents troubles during playing (from DVD) : the image lags nearly to a halt and pixelization.
If such files are played from the hard disk the playing is normal.
Perhaps the DVD player has not transfer ratio enough to keep fluid motion.
Is there anything I can do to overcome this trouble ?
thanks