Avidemux 2.5.6 uses all CPU cycles...

[abrogard]

  I have an Athlon 64 3200 on an Asus A8NSLI with a Sapphire Radeon X800 video card.

Avidemux has been loaded with an MP4 file made by Atube Catcher from a Youtube download.  I just want to cut out a small segment of it.

Avidemux loads and runs it okay but I can hardly get any mouse pointer movement. It is all jerky and/or slow or nothing. 

I've never seen this happen before. 

And I've used Avidemux before - though it was so long ago I don't remember anything about it except that there were no problems ( I remember the problem software ) ....

Anyone got an idea what might be happening?  I think my system should be good enough for  this little task, surely?

When I looked in task manager Avidemux seemed to be taking 85% of cycles.

Am I perhaps doing something wrong - having it try some sort of conversion when all I want it to do is play the thing until we get to the area I want to put a marker in as the start of my segment, then move onto the end, mark, cut, save, finish.

[Jan Gruuthuse]

Try with 2.6.1? What is your operating system? If that mp4 is with h264 or avc encoding, that could be an cpu processing power issue?
Upload a 5 second similar video clip to rapidshare or similar and provide a downlink to it. Could be something funny is going on with that video?
Sapphire Radeon X800 video card won't be a big help either? Hardware over 5 years old or even older?