1 pass and 2 pass bit rate query

[socrates]

I have been downloading brrips and with virtualdub, converting 720p and above to 480p to view in my TV. I have read somewhere that it was always better to use 2 pass to convert 720p and above mp4 to 480p avi because of intelligent bit rate analysis. Also it was mentioned that 'higher' bit rates would not show much difference between 1 pass and 2 pass. My query is how much is this 'higher'? I can save time if I know above which limit, 1 pass will be sufficient. Please comment. Thank you

[Case]

You could use XviD, Single Pass, Target Quantizer="2.00" to get a very good quality encode in a single pass, by letting the encoder use whatever bitrate it needs for quantizer value 2. Basically you set the compression level, which is close to what viewers perceive as constant quality. The bitrate and output size will be unknown beforehand, because this is encoding for quality, not size. Use a "typical action" short test clip with varying quantizer values to find your personal optimum.

H.264 uses a different scale, so you need a different quantizer value for that codec. "10" would be a good starting value.