Xmedia recode options

[ro2124]

Been using xmedia recode mainly to make file sizes smaller and by using lower bit rate .
although the program can be rather slow getting some reasonable results.
however somewhat confused with some of the options of which there are many.
I am using avc/h264 setting with average bitrate.
I'm a bit confused about the "level" settings.
does changing levels affect file size a lot?
and how do they affect the quality?
at the moment I have opted for the mid-range which is 4.

and for profile using "Main" although there are three others, no idea what they do in regard to file size and quality.
perhaps someone could enlighten me on all this

[raffriff42]

Profiles and levels have to do with hardware player capabilities. For PC playback use "auto" level and "high" profile. For devices, use the nearest XMedia profile.