3 pass multipass the same as 1 pass multipass done 3 times?

[Letricheur]

This may seem like a dumb question but is doing 3 separate single "multipasses" in CCE the same as doing a 3-pass multipass all at once? I ask because I can't afford to tie up my computer for too long and yet I want 3-pass quality. My idea is to do a modified Robshot, starting with a 1-pass VBR (constant quality), saving the *.ecl and *.vaf files. Then, on another occasion, open the *.ecl and run a mulitpass VBR with a pass number of 1, again re-saving the *.ecl and *.vaf files. I will then do 1 or 2 more runs of multipass VBR with a setting of 1 pass.

This is much the same as the Robshot method except that I repeat the second step a few times in the hope of simulating a 3-pass multipass. My intuition tells me that this should produce the same result but am interested to hear if anyone knows this for sure.

[jdobbs]

It doesn't matter whether you do the 3 passes all together or run a single pass (in multipass mode) 3 times. It's the same -- but make sure you don't keep saving and restoring the .VAF file. The improvements you gain in a plurality of passes are stored in the .VAF.

FUN EXERCISE:
Got a lot of time on your hands and you want to see what the best picture you can get from CCE is? Try this some time:

1. Do the first pass using Robshot's method, and set the parameters according to his guide.

2. Instead of one second pass , set two different output file names (call them "output-a.m2v" and "output-b.m2v". Then set the number of passes to 9.

Then let the thing run overnight, until it finishes, or until you need your computer again and hit the "Cancel" button. Look in your output directory and there will be the two files mentioned above. Delete the shorter of the two -- it was the file being written when you canceled. The other is the most recently written MPEG-2 file that was fully completed.

Note for the sticklers: I know that CCE says quality reaches its limit after 3-4 passes. But what the hell, you have to try it once, right?

[Letricheur]

Thanks! That's just what I needed to know. One question, though. Should I be saving the *.vaf file to a different name with each pass?

I'd also like to try your suggestion of comparing the 9 passes, jdobbs, but will have to wait until I get a second computer.

[jdobbs]

Keep the .VAF file with the same name and in the same directory through all passes. It's alright to back it up somewhere (copy it) so you feel safe.

The time to be careful is if you decide to do something other than a multipass encode. For example, if you decided to do a constant bitrate pass after several multipasses, the .VAF is destroyed and created from scratch again causing you to lose any information gained from the multiple passes.

[wmansir]

I'm not sure if this is entirely true. I just checked the modified date of my .vafs for the last movie I did and noticed that it doesn't change after multiple passes. You would think if the .vaf was updated on each pass the modified date would change also.

[jdobbs]

That just means the file wasn't closed between passes.

Here's a quote from the CCE manual:

"What is video information file? Generally at least two
passes are required to create variable bitrate stream for spec-
ifying an average bitrate. This is because the complexity of
images is checked and saved in a file by the frst pass, and the al-
location of the bit amount for each frame is calculated according
to the stored information on the complexity of the images, and
encoding is executed in the next pass. Unlike a general encoder,
Cinema Craft Encoder does not distinguish between a pass for
encoding and pass for analyzing complexity, but always an-
analyzes the complexity of images during encoding. Therefore,
a video information file does not always have to be recreated
to change the setting of an average, minimum and maximum
bitrate.

A video information file has a history of information for a plu-
rality of times of encoding, and information is accumulated each
time encoding is executed. This information improves the image
quality for encoding by the Multipass VBR system."


In fact the "how" example in the manual actually uses One Pass VBR or CBR to create the .VAF before then changing to Multipass.