Question to the AV OUT - does the 5d has also a AV OUT?
And which cable i need, and can i use an external monitor for live view with this?
Which resolution? PAL/NTSC??
Can't speak for 5D but the 7D definitely has AV out. It comes with a cable. Resolution is SD. I've used it on NTSC but not PAL, but I don't really see why that should make a difference. The thing is that AV composite (RCA) can only support SD, so you kinda know what you're going to get going into it.
If one's projects are SD, as I live in Beirut, and no one has adopted HD still, is the signal from AV out of good quality? I bought both my GH1 and 7D to use as SD machines anyway.
Both 5D and 7D have an AV out, it is composite at 480i, through a proprietary cable that comes with the camera. The signal is not of particuarly high quality: it is composite, afterall, and also suffers from being letterboxed to 16:9 with a red dot screen overlay that can not be removed.
As for which is better AV or HDMI... there is no question that it's HDMI on the 7D (this is the 7D forum, mayeb your question would be better placed in the 5DmkII forum?) and I'd probably say it's still HDMI on the 5DmkII as well, simply because HDMI is digital instead of composite analog. But it's pretty bad either way, while recording. When not recording, both the 5DmkII and the 7D output high-resolution 1080i