Problems with video resolution

[ddg1]

First of all, I should say that I have an Atom CPU and a GMA500 GPU and I'm using the psb_gfx driver. I know it's not a well supported card and it has poor acceleration (I have to use the x11 output driver), but videos play fine, even h264 at 720p resolution. However, I have some weird problems that I can't find a solution to.

Depending on some factors apparently related to the resolution, the video stutters a lot, to the point of being unwatchable (the sound plays fine, though). Actions like resizing the window seem to affect it, with some sizes working well and others stuttering. It also happens with the zoom factor: 1.0 plays fine, 1.05 doesn't, 1.10 does, etc, although for other videos it's different (1.0 and 1.05 stutter, 1.10 and 1.15 don't...)

This doesn't happen with mplayer nor with gnome-mplayer, only with smplayer (and smplayer2). It also doesn't happen by executing the same command as smplayer, copied from the log. I've tried changing all the settings in the video, performance and advanced sections, but nothing worked.

Does anyone know why it might happen and if there's a solution?