Comment 9 for bug 104630

I too was having this problem.

I downloaded the source with apt-get source and twiddled with various CFLAGS and configure knobs, but really that was a waste of time, because i get a working mplayer binary with CFLAGS empty and no defaults on a G3. My guess is that this is a bug in the mplayer configuration system - they sternly warn you not to override CFLAGS (even if it's to provide a more compatible -mcpu= option!) If I add -mpowerpc-gpopt to CFLAGS, boom, the SIGILL's come back. Remove them again, and it builds fine. These CFLAGS, for example, work fine: "-mcpu=750 -Os -pipe -fno-strict-aliasing -mpowerpc-gfxopt"

I was very surprised to find that this resulted in a usable build of mplayer on this ol' G3 @ 400MHz. I can watch a 624x352 XviD without altivec. Only catches are that cpu usage is at 100% and there is the occasional dropped frame, and that the default audio out (oss) makes human voices scratchy and unlistenable. -ao alsa fixes that right up though.

In any event, here's how I did it for those of you playing along at home:

#NOTE: apt will pull in some prerequisites - keep track of these if you want to delete them later
sudo apt-get install libx264-dev libxvidcore4-dev libfaac-dev libasound2-dev libxv-dev libfontconfig1-dev
cd /tmp
sudo apt-get source mplayer
export CXXFLAGS="" ; export CFLAGS=""
./configure --enable-largefiles --disable-tv --disable-pvr --disable-tv-v4l1 --disable-tv-v4l2 \
--disable-tv-bsdbt848 --disable-unrarlib --disable-inet6 --disable-ftp
make && sudo make install

I also had a successful build with these CFLAGS, but haven't compared the two for performance or anything like that:
export CXXFLAGS="-mcpu=740 -Os -pipe -fno-strict-aliasing -mpowerpc-gfxopt" ;
export CFLAGS="-mcpu=740 -Os -pipe -fno-strict-aliasing -mpowerpc-gfxopt" ;

It takes between 20 minutes (with -Os) and 30 (with -O4 as mplayer's config script defaults to) to build the binary. You'll almost certainly want to add -maltivec if you are compiling on a G4.

I'm sure that even on my system there is more to tune, but I'm not running gentoo here, so I'm happy for the moment ;-)

Good luck!