2-pass encoding?

[andyx181x]

hi there guys, i pretty much been using handbrake, mac the ripper, and ffmpegxx to do my movies in avi and everything is well. however i just wondered, what does an extra pass in encoding do? i pretty much been leaving handbrake to do a 2 pass, while with ffmpegxx i leave it as a single. is it just a means of compress size more? am i losing some quality by doing a second pass?

[thecoalman]

The first pass doesn't encode anything. All it does is examine the video to determine how to best distribute the bitrate. The second pass does the actual encoding.