TMPGEnc’s Rate Control Mode tradeoffs

[Mikeysoft]

I read this site’s newbie section on TMPGEnc. I have some questions on 2pass Variable Bitrate(VBR), Automatic VBR, and Constant Quality(CQ):

These are my understandings and may be wrong so please correct me.

2 pass Variable Bitrate(VBR)
Advantage:
File size can be predicted.
The total file is scanned, when the average Bitrate is above the average set, the max bitrate is lowered a little throughout the file so that it will have least affect on quality to get the average set.
Disadvantage:
Should the average bitrate be below the average set, padding will be set to bring the average up to the set average. This will make the file larger then needed.

Bitrate(VBR), Automatic VBR
Advantage:
The quality of the file will be what is set up to the maximum quality allowed by the max bitrate set.
The file size may be smaller then a CBR set to the maximum.
Disadvantage:
The file size may be the same as CBR at the maximum bitrate set.
Question:
The bitrate is set until a scene change. What is a scene change? Is it a cut. It so, are cuts with dissolves consider the same scene, or does it have something to do with I, B P? If it has to do with I, B P, about how often and why are screen changed generated?

Constant Quality(CQ)
This look similar to Bitrate(VBR), Automatic VBR, except you can set the P & B picture spoilage.
Question:
What is P & B spoilage? Does it have something to do with generating a scene change. What do the numbers for spoilage mean?


All inputs, correction, and clarifications are welcome.

[Mirror_Image]

This might (or might not) help:

http://tangentsoft.net/video/mpeg/enc-modes.html

[banjazzer]

Although this is a contentious issue, many think that TMPGEnc's CQ mode is superior to it's 2-pass VBR mode. This would also appear to be the view of TMPGEnc's creators if you read their helpfile on encoding modes. I prefer CQ because it is much quicker, despite needing a few test encodes to predict final filesize. However, both 2-pass VBR and CQ will give excellent results when used sensibly , and in the latest version (2.57) the 2-pass VBR has apparently been improved.

[Mikeysoft]

banjazzer,

The 30 day free trial version does not have a help file so thanks for your help.

Mirror_Image,

Thanks for the link. It did help.

Anyone,

I think P & B spoilage changes how offtem the encoder changes a "scene change" to compute a new bit rate. Correct?

Does anyone have more inf on P & B spoilage?

[banjazzer]

From TMPG's help:

Constant Quality (CQ)
When one is more concerned about picture quality than file size, one should use this mode. Using the CQ mode, one can set all of the aspects of quality to use in the encoding. This mode will guarantee a high quality movie; however, movies with many scene with rapid motion can become rather large.

This is not exactly proof - rather a clue. 8)