Auto VBR vs. 2 Pass VBR fro TMPGEnc

[rhuala2]

Aftering reading many tutorials/how-to's it seems like sometimes Automatic VBR is used whereas other times 2 Pass VBR is used. I am inclined to always just use Auto VBR, I haven't noticed a signifcant change in file size or quality using one or the other. What is the basic rule of thumb for these? How can you go wrong by always choosing Auto VBR. The TMPGEnc explained section on this site states:

2pass Variable Bitrate(VBR): This means that your bitrate has an minimum, maximum, and average bitrate. On this one you can set the average to a fixed setting and have it either raise to the maximum you set during high motion scenes or fall to the minimum you set when there is little motion. This setting is good for figuring out the size of the file that is being outputted and to have it reach higher bitrates yet still maintaining a lower file size. under the settings of this setting is where

Automatic VBR: This is pretty much the same as above (manual VBC) but it does it figures out what to set its bitrate to on its own. It also has a maximum, minimum bitrate, and padding feature. but also lets you set the quality of your encode, the higher the number the better quality but bigger file size.

I have been using 2 Pass VBR a lot and cranking the bitrates when I have high motion captures but to be honest auto VBR seems to do just as good a job. Which begs the question, why don't the majority of tutorials use Auto VBR, especailly for simplicity? Someone please set me straight on this. Thanks,

Rob

[fantomlord]

the advantage to using 2 pass VBR is that you will know how big your file will be after you encode, where as with auto VBR, you can't be positive beforehand
this is useful when you know that your trying to fit a movie onto 2 discs, for example, and you wish to fill the discs completely.

[banjazzer]

And if you want the best possible quality with TMPG, some think you should use CQ mode, including me. And the creators of TMPG, if you go by their manual. "When one is more concerned about picture quality than file size, one should use this mode." 8)

[SingSing]

the advantage to using 2 pass VBR is that you will know how big your file will be after you encode.

I though any type of VBR will not let us know the file size ahead of time.
Unless the min,max,and avg are all very close, then why VBR at all?

[LanceSteel]

I though any type of VBR will not let us know the file size ahead of time. Unless the min,max,and avg are all very close, then why VBR at all?

I've found that 2-Pass VBR gives me a file which is sized very closely to what I calculate before hand (+/- 10MB or so.) Usually, I just leave the High and Low alone (8000 for high, 2000 for low) and vary the average.

[banjazzer]

I though any type of VBR will not let us know the file size ahead of time.?

The size of an x-pass VBR encode is determined by the average bitrate, so you can closely predict the filesize.

Unless the min,max,and avg are all very close, then why VBR at all

If they were all very close you may as well use CBR. VBR is most useful when there is a reasonable spread between min and max, and the average lies in the middle.