Right now the problems with video support on n800 are related to video output drivers.

Nokia 770 has the following options for video output (-vo option):
* sdl (no hardware YUV colorspace support and slow software scaler)
* nokia770 (hardware YUV support using framebuffer direct access and optimized scaler, right now it is default option)

Nokia N800 has the following options for video output (-vo option):
* sdl (no hardware YUV colorspace support and slow software scaler)
* xv (theoretically the best video output method, it is hardware accelerated and provided by xserver bundled in n800 firmware)

Now the bad news. Looks like video output in n800 using xv is rather buggy both in built-in player (see some reports here) and in mplayer. Video output using 'nokia770' driver does not work on n800 yet. First, screen update ioctl seems to ignore YUV color format flag and works with RGB (green colored garbage), pixel doubling is not supported anymore, also JIT scaler crashes on n800 (apparently some problems with cache coherency for dynamically generated code). The only more or less reliable video output method for n800 currently is sdl, but it is very slow.

BTW, there is no surprise that built-in player is a bit more stable, at least I'm sure that testing and quality assurance in n800 firmware was done for it, but not for mplayer

So what can we do right now? In the long run we can expect some bugfixes for libxv in future n800 firmware updates. Another alternative is to experiment with framebuffer ioctls and update 'nokia770' video output code to work with n800 (xserver sources provide some insights about how it should work, I'm checking this code now). With some luck, we may expect a n800 ready build of mplayer soon (if a bug is only in xserver but not in kernel framebuffer driver, otherwise a fixed firmware will be still required).

Well, I already got my n800 on last Sunday, but did not have enough free time to do anything with it till this weekend