I've wondered for a while why Mplayer (a video player for Linux) complains about not having permission to use /dev/rtc (the Linux real time clock interface) for it's timing. It works as root, but I don't want to be using a video player as root.
It turns out that this is not because a normal user can't access the RTC
driver—in fact any user can, but only root is allowed to use it for
generating clock ticks faster than 64Hz. The kernel documentation admits
that this might be a conservative limit, but says “we don't want
an evil user generating lots of IRQs on a slow 386sx-16”. Since my
desktop machine has a processor clock speed about 100 times that, it seems
reasonable to up the limit. This has to be done by tweaking the kernel
source—in drivers/char/rtc.c change the value of
rtc_max_user_freq to 8192 (which is the maximum frequency) to allow
any user to get full access to the RTC.
Another annoying thing about Mplayer: I usually watch small videos scaled
to twice their actual size. That's usually a bit smaller than my screen
size, but scaling them to the full screen size is a lot slower (it's easier
to scale by a factor of exactly 2). I used to be able to do that with
the options -xy 2 -zoom, but now that doesn't seem to work. I've
discovered that using -vop 2xsai does the trick. It wouldn't be
any fun if this was easy, now, would it?