I have Slackware 14.1 on a Core 2 "HTPC" computer used for watching video.

Yesterday, everything was fine. However, today, mplayer lags. It lags in a way that makes it show approximately 10-15 FPS on a typical video that I know should have 25. On any other computer that I have, the video runs smooth and appears to be 25 as it is, while on this HTPC machine, every video now appears to run at around half the real FPS.

When I run mplayer from the console, I get no warnings or errors, especially not the infamous "YOUR SYSTEM IS TOO SLOW".

CPU usage is around 5%.
Most of the memory is free (80-90% free).
I have tried to play the video over both network and from local disk, it makes no difference.
I have tried to reboot.
I have tried to reinstall the NVIDIA drivers (Quadro FX 370).
I have tried to disable vdpau and run everything in software rendering.
I have tried different types of media files. Strangely when playing a video in the flash player in Youtube, it looks fine. But in mplayer, everything lags.

I have looked at dmesg for anything suspicious.
I have executed mcelog to look for MCE errors.

Nothing makes any sense to me. Intermittently, for maybe 2-3 seconds, the video will go up to 25 FPS, before it drops back down to a choppy 10-15 FPS.

The size of the media file and the encoder used doesn't appear to make much difference, but some appear worse than others. But even small files exhibit this behavior.

How is it possible that this would work yesterday, but fail to work today? I have made no changes whatsoever to the system.

I had that problem with an old laptop. But I discovered it was a problem with HD, for some strange reason the DMA was turned off.

you can check with

hdparm -I /dev/sdX

Unfortunately this is not related to my problem. If I was using PIO mode, my CPU load would be higher, and even PIO mode probably wouldn't be a problem for small video files on a Core 2 system.

As I mentioned I also have this problem over the network too.

But I checked anyway, I'm using DMA.

Perhaps cut the Gordian knot and simply try compiling a newer version, current svn is quite stable...