Multiplexing audio and VBR-encoded video

[walter4h]

Hi, guys:
I have to multiplex m2v and ac3 with a 3rd-party multiplexer. I have a question with this regard - if I have captured video, then encoded it into M2V with VBR - can I multiplex it with AC3?
When I extract audio from the captured AVI file, the extraction program "does not know" that I am going to encode the video at VBR. And if the timecode does indeed move back and forth along the timeline during VBR encoding, here seems to be a potential problem when it comes to multiplexing.
Here is an excerpt from Cinema Craft Encoder guide which provoked this question:
<<If you want the amount of bits in each GOP to be the same, select CBR,and if you want the quality of each frame to be the same, select VBR. Note, however, that if you select VBR or 1-pass VBR, AUDIO MULTIPLEXING WILL NOT BE PERFORMED.>> (emphasis mine)
The question boils down essentially to this - can I safely encode an elementary video stream in VBR if I intend to multiplex it later?
Thx Walter

[dafreak]

yes.

as long as you're not changing the framerate of the video, ie. changing the framerate from 25 to 29.97, it shouldn't affect your video/audio synch.

And if the timecode does indeed move back and forth along the timeline during VBR encoding, here seems to be a potential problem when it comes to multiplexing.

I dont' know where you got this from, but vbr does not change the timecodes at all. At least not that i know of.
vbr makes 2 passes. first pass encodes the video with constant quality, and then the second pass will increase/decrease bitrate depending on what is going on in the movie. ie. increase in bitrate with action sequences, decrease bitrate if there is little to no action, etc.

[walter4h]

Thanks,
just to make sure. I was confused by that passage from CCE guide. I thought maybe the timecode delivery is not held at the same rate at VBR. Now I can safely encode at VBR and have shorter files.
walter