Did you do a system upgrade? Is the testing repo enabled?
Yes, i upgraded today, but without enabling the testing repo.
What of the other video players mplayer, umplayer, gnome-mplayer?
Yes, those. The only player that works for me now is Xine (It started to work again since i upgraded everything, strange, because i already had xine updated, both lib and ui). When i try to run a video in UMPlayer (Porn, Movies, etc. Generally in H264) using the "Open With" option the program starts but it doesn't play the video. It's the same if i start the program and then load the video. Gnome MPlayer does the same thing with the music, the program starts, the music (MP3's or OGG's) doesn't play. No errors showed up.
Installed VLC too form the repo and it doesn't even start. My system: AMD Athlon 64x2 Dual 5600+ 2.91GHz (But i use 32 bits version of Vector), almost 2gb of ram, NVIDIA 6150SE NForce 512mb, installed the official drivers.
Tried downloading a pack of codecs from softpedia and installed all of them in /usr/local/codecs and /usr/lib/win32 if i remember well (I copied the files and gave 755 permission with chmod, just like the guide said), but it didn't help.
I play Postal 2 (A game, linux native, unreal engine 2) a lot, and both, audio and video (cutscenes) worked well without doing any tweaking.
EDIT: Decided to install Vector Light with LXDE. XFCE wasn't running slow, but i wanted to be in LXDE
This time seems i can play music with "Music Player", didn't tried yet Xine for video. MPlayer (Apparently a different program from Music Player, because the other works well) won't start. Tried running it from the console and it said "mplayer: error while loading shared libraries: libvpx.so.0: cannot open shared object file: No such file or directory".
P.D.: Before doing anything, after installing, i upgraded my system with slapt-get.
P.D.2: English isn't my main language, so if i write something wrong, you know why.