[popcornmix]

thanks for the explanation are there any advantages of using dvdplayer instead of the default (just on the raspi) omxplayer? like for instance less resources or something?

dvdplayer on Pi is very experimental, so it's recommended for people who want to help testing as in the future it may be used as the default player in more situations.

The clear benefit is omxplayer has no support for DVD menus. dvdplayer does a much better job (although there are still some issues currently).

It is possible dvdplayer (as it's more widely used and tested and supported by more devs) will behave better in some situations (e.g. live tv, dvds, streaming plugins).
It also does things differently (like audio amplification) which may or may not be preferable.

It could be better or worse with issues like image quality, audio sync, buffering, stabilty, cpu uage, memory usage.

But, that's why it's out for testing in a *test* build. If you just want trouble free video playback and are happy with current behaviour then ignore dvdplayer (and avoid these bleeding edge builds).
If you want to help make xbmc on Pi better, then please test. Ideally do comparative tests running omxplayer and dvdplayer on the same file and watch carefully,
and explain the differenced you can see or measure (e.g. memory cpu usage with bcm_stat.sh).

IMO:
dvdplayer is a little quicker to start and seek (doesn't require the gpu fifo to be filled). Rewind/ff should be more stable.
Better dvd menu support. Should avoid some issues with live tv with errrors causing stalls and sync issues.

omxplayer uses less CPU and (gpu) memory. It is better with high bitrate 1080p. It has theoretically better image quality (resizing).
Handles short period of arm being busy better.

I would guess that video smoothness (getting exactly one frame per vsync) probably varies with content.
omxplayer is theoretically better (being able to control hdmi clock), but dvdplayer may handle problematic files better (e.g. dodgy timestamps).