I also reported this problem before.
It seems that it can't be solved.
Quote from
http://smplayer.berlios.de/forums/viewtopic.php?id=1499---------------------------------------
ASSUME:screen resolution = 1024 x 768
Preferences -> General -> Video -> Default zoom = 1
original size of sample.wmv = 640 x 360
When the sample is played in fullscreen,
actual size of sample.wmv = 1024 x 576 //note: 1024*360/640=576
press the W key 1 time, size: 973 x 547 //note: 1024*0.95=972.8; 576*0.95=547.2
press the W key 2 times, size: 922 x 518 //note: 1024*0.9=921.6; 576*0.9=518.4
... ... ...
press the W key 7 times, size: 666 x 374 //note: 1024*0.65=665.6; 576*0.65=374.4
press the W key 8 times, size: 614 x 346 //note: 1024*0.6=614.4; 576*0.6=345.6
In fact, I feel like to see the sample with its original size in fullscreen.If I press the W key 7 times, it is bigger than 640 x 360
If I press the W key 8 times, it is smaller than 640 x 360
So, I WISH:if( fullScreenSize != originalSize ){
dblclick the screen 1 time, see the sample in fullScreen(1024 x 576);
dblclick the screen 2 times, see the sample in originalSize(640 x 360);
dblclick the screen 3 times, see the sample out of fullScreen;
dblclick the screen 4 times, fullScreen again;
... loop ...
} else {
dblclick the screen 1 time, see the sample in fullScreen(1024 x 576);
dblclick the screen 2 times, see the sample out of fullScreen;
dblclick the screen 3 times, fullScreen again;
... loop ...
}