Thanks for the reply, Texstar. I'm not going to install VLC, because I found Gnome Mplayer

. I tried it to play the video and it worked well. Well, it's indeed Totem's problem, not the OS

.
By the way, I also have the same problem that I got on another distro, that sound from netbook's speakers comes out while headphones get plugged in. The speakers are supposed to get muted, right? On Ubuntu I got this problem and then made some scripts in alsa-base.conf (snd-hda-intel option) following tips I found on some forums. But it didn't make the problem gone. I wonder if you have some solutions for this? Thanks.