Mplayer: 704x576 image cannot fit on 800x600 display?
 

I am continuously trying to play movies at (nearly) full screen on my modest hardware (AMD K6 450, NVIDIA GeForce MX 200, 192M RAM), but I always fail for different reasons.

Lately I tried to play an avi file (a movie) that has a 704x576 image size, using the x11 device:
mplayer -vo x11 -vm movie.avi

I saw mplayer choosing a video mode of 800x600 for playback.
However, to my surprise, the y dimension of the played image stretched over the visible screen by cca. 10%. I could scroll the image to view the top or the bottom, but I could not see the whole image at a time.
How can this happen when the y dimension of the image should be smaller than the y dimension of the screen?

Here is the relevant part of the mplayer output:
---
Starting playback...
This file was encoded with libavcodec build 4655
VDec: vo config request - 704 x 576 (preferred csp: Planar YV12)
VDec: using Planar YV12 as output csp (no 0)
Movie-Aspect is 1,22:1 - prescaling to correct movie aspect.
VO: [x11] 704x576 => 704x576 Planar YV12 [vm]
XF86VM: Selected video mode 800x600 for image size 704x576.
Using MMX for colorspace transform
SwScaler: using unscaled Planar YV12 -> BGR 16-bit special converter
---

I found the same when using the dga device, or worse: I could not even scroll the image there, the top and bottom 5% of the image was lost.

Accidentally I have an other version of the same movie, which has been re-scaled to 576x448 image size.
It is funny, but I cannot play this movie correctly, either: because mplayer now automatically chooses 640x480 video mode, and a part of the image is invariably lost...

When I select the fbdev device for playback, the upper 1/3 of the kde desktop is filled with continuously moving lines as if a movie was played there, but there is no visible picture as the lines are totally out of sync. However, when I switch to console (pressing CTRL+ALT+F2), I see the correct picture there, but it is small (probably because my screen mode under X is 1024x768?).

When I select the vesa device for playback, the latter movie (the 576x448 one) is played correctly and at the original size (i.e. almost full screen).
One could think that there is no problem: I should stick with the vesa driver.

But that is not so simple: there are VCDs that I cannot play at (nearly) full screen, because they need much scaling (zoom), for which my system is too slow (audio and video falls out of sync).
The mplayer manual says that the x11 and dga devices are superior to the vesa one when it comes to scaling the image.
In most cases I have only a slight video/audio sync problems with the vesa device, so, if the x11 or dga devices can scale the image really faster, then maybe these could be my choice to play all movies full screen.

My questions are:
- are the x11 or dga devices really faster than the vesa to scale the played image?
- the 704x576 and the 576x448 images why cannot fit on 800x600 and 640x480 screens, respectively?

Could you help me?