Rendering with dual pass makes smaller file?

[Pat Brown]

I rendered two identicle clips as .wmv files using windows media 8 codec. On one I set it up to do dual pass. This clip took twice as long to render but the file size was about 20% smaller.

I have a few question; why is this, is this consistent with what any of you have experienced and also what is dual pass exactly?

[docrhody]

That works with all codecs and encoders. You get a smaller better looking file (it's why you use 2-pass). Set it up to batch encode and let it run all night.

[Gazorgan]

That's not necessarily true.

Properly done 2-pass isn't any smaller than a 1-pass. It's 'better' as it's allocated more bitrate to the scenes that need it more and robbed the scenes that need it less.

The fact your 2-pass is smaller indicates a problem. What did you use to encode it with? WMV can be as good as DivX/XviD, but you have to really work at it (that menas non default options).

WMV is an odd duck, in that it removes a lot of encoding decisions from the normal interface. It assumes the user is an idiot (64 kbps is not DVD quality audio), and has a lot of marketing types driving the stats. It also has a Variable framerate, which can save bitrate but have interesting sideaffects.

[Pat Brown]

The fact your 2-pass is smaller indicates a problem. What did you use to encode it with?

I am using Vegas video 4 with uncompressed .avi files. I'll try rendering some different clips making sure that the settings are identical, except for dual pass, to confirm that this is really happening.