That bug has been described on https://launchpad.net/distros/ubuntu/+source/gstreamer0.10/+bug/32894

"When I play oggs with rhythmbox, it takes 100% of one cpu.
I use a powerppc with 2 cpu with Ubuntu Dapper.
...
> Thanks for your bug. Does it happen if you use "gst-launch playbin uri="file://path/to/ogg" to play them? Does that happen with all the ogg or only one?
...


Yes, it's still loading a cpu.

Here is the output of gst-launch, interrupted by a ctrl-c :
---------------------------------------------------
OIL: ERROR liboiltest.c 403: oil_test_check_impl(): function conv_f32_s16_bitstuff in class conv_f32_s16 failed check (37,7031 > 0,1) || (outside=0)
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
New clock: audioclock4
Caught interrupt -- Pausing pipeline.
Pipeline paused.
WARNING: Element "playbin0" warns: pipeline interrupted
Element "playbin0" has gone from PLAYING to PAUSED, quitting. Execution ended after 8029122000 ns.
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
FREEING pipeline ...
...
> Does it happen with all the ogg or only one? Could you get a backtrace? - gdb gst-launch
(gdb) run playbin uri="file://path/to/ogg"
... ctrl-C
(gdb) thread apply all bt

And copy that to a comment
...
> What audiosink do you use from gstreamer-properties? Could you try changing it?
...


Using gstreamer-properties, I have autodetect, alsa, esd, oss and custom settings for audio output.
It was on autodetect before.
Alsa and esd load the cpu.
Oss give an error message :
 Error running pipeline 'OSS - Open Sound System': Unable to open device /dev/dsp for writing: Périphérique ou ressource occupé [gstosssink.c(388): gst_oss_sink_open (): /pipeline0/osssink1]

I am using a custom kernel but It behaves identical with ubuntu kernel. I was thinking about timer issue as it seems an active wait ? maybe dev/rtc problems ?
...
> Could you attach the backtrace as an attachment without all the extra lines from the previous comment?
...
fredo@ange:~$ gdb  gst-launch-0.10 
GNU gdb 6.4-debian
Copyright 2005 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "powerpc-linux-gnu"...(no debugging symbols found)
Using host libthread_db library "/lib/libthread_db.so.1".

(gdb) run playbin uri="file:///home/fredo/Desktop/a.ogg"
Starting program: /usr/bin/gst-launch-0.10 playbin uri="file:///home/fredo/Desktop/a.ogg"
(no debugging symbols found)
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread -134402048 (LWP 5001)]
OIL: ERROR liboiltest.c 403: oil_test_check_impl(): function conv_f32_s16_bitstuff in class conv_f32_s16 failed check (42,6641 > 0,1) || (outside=0)
Setting pipeline to PAUSED ...
[New Thread -135969552 (LWP 5004)]
Pipeline is PREROLLING ...
[New Thread -144358160 (LWP 5005)]
[New Thread -154143504 (LWP 5006)]
[Thread -154143504 (LWP 5006) exited]
[New Thread -154143504 (LWP 5007)]
[Thread -154143504 (LWP 5007) exited]
[New Thread -154143504 (LWP 5008)]
[Thread -154143504 (LWP 5008) exited]
[New Thread -154143504 (LWP 5009)]
[Thread -154143504 (LWP 5009) exited]
[New Thread -154143504 (LWP 5010)]
[New Thread -162663184 (LWP 5013)]
[New Thread -171051792 (LWP 5014)]
[New Thread -179440400 (LWP 5015)]
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
New clock: audioclock4
[Thread -171051792 (LWP 5014) exited]

Program received signal SIGINT, Interrupt.
[Switching to Thread -134402048 (LWP 5001)]
0x0fc35228 in poll () from /lib/libc.so.6
(gdb) thread apply all bt

+ Trace 66538

The program is running.  Exit anyway? (y or n) y

This is a backtrace of gst-launch playing an ogg and taking 100% cpu. gst-properties is set on 'auto' for audio output."