apart from what is obvious (the meaning of average and target)...what does it change? is there any adavantage in average over target?
and it's very strange that 2 pass are for average. other encoding softwares have 2 pass for target (i think it requires more precision) and 1 pass for average
What particular encoder do you have in mind?
In case e.g. of x264, 1 pass encoding is either for constant bitrate (the worst possible mode), for constant quality (the best possible mode when no bitrate / bandwidth restrictions apply) or for constant quantizer (worse = more wasteful than constant quality).
2 pass encoding makes sense only when bitrate or output size limitations exist (output size is used to calculate average bitrate, so ultimately it is just one and the same mode).
Target bitrate mode (CBR) means the encoder adjusts quality to keep the bitrate close to the specified value. This is the mode you should avoid whenever possible.
but that is the peferct mode for me. just 1 pass (faster) and he keeps the size i want
with CRF the output file could be bigger (useless, not more quality) or smaller (loss of quality). there is no way to know which value will keep the same size