MEncoder Two-Pass Encoding

You can use the bitrate option with one or two pass encodings.

Ripping a video with a two-pass encoding will result in higher quality than in simply one pass.

Single pass will take your clip and encode it at once. It takes each frame of the clip, checks that frame's compressibility, and then encodes it.

Two-pass uses the first pass to make an estimation of how well your clip compresses and then uses the compressibility data gathered during the first pass to really encode the clip during the second pass.

Which one to choose depends on what you desire from the result. Two-pass does a much better job at evenly distributing bits where they are needed and therefore gives you a much better looking end result. Generally what you do when you use this option is to calculate motion compensation and other non lossy compression related tweaks (qpel, trellis, gmc. bframe placement. etc) and then on the second pass where the compression is done. Single pass is really for those type of uses that can only be done with single-pass, like for instance real-time encoding a live feed, like a TV-capture or a security camera. Unless you absolutely have to go for single pass for a specific reason there really is no other way but two-pass."