you said you cannot see the difference between a 1-pass and a 2-pass mode. You may not see it but it’s there. Do a small test, for example encode only 1 chapter of a DVD in 1-pass mode and then do exactly the same but this time use 2-pass. For both tests enable the PSNR option (or for x264 also the SSIM one) and you’ll definitely see the difference between 1- and 2-pass (make sure to use exactly the same options in both tests). Maybe your eyes are not so tuned to spot differences in quality that easy or maybe you have a “bad” monitor, i don’t know, but a 2-pass encoding at a (very) low bitrate will definitely beat 1-pass mode. This comes from the fact that the encoder is “dumb” when used in 1-pass mode and cannot predict the complexity and motion of a future frame, which eventually leads to blocking and other weird effects, unless you give it a bitrate high enough to eliminate these issues, but then you’ll be wasting bits. Not so when using 2-pass mode since the first pass will be used to store information of every frame to a log file and then when the second pass starts, the encoder will read the log file with the frame/motion/complexity information for each frame and base its decision how much bitrate to allocate for each frame.