Rate control in XVID

[ExperimentalAnimations]

From the doom9 xvid tutorial:

Then we have the Rate control, where you can choose between applying a different Weight to the bitrate, or specify a Quantizer (compression factor). As you can see, I have chosen a weight of 0.15, which means that the end credits will get 15% of the bitrate of the main movie. However, you might want to use a fixed quantizer in the range of 20 for now as the weight option seems to be bugged.

1. Is the weight option still bugged?

2. The weight option goes above one, it actually goes to two, meaning you can get 200% of your total bitrate. What?

3. There is no documentation anywhere on what the different quantization levels do (except for math formulas), however i set it at one halfway through my video, and the first half was a smeary mess and the second half was sharp and blocky. The only info i can find on quantization involves it being set to 1-3, but nowhere does anyone mention why there are 30 levels of it, or why GUI's like automkv like to set it at 20.

4. If i allocate 15% of my total bitrate to half of a video, does the other half get 115%? Does giving one half of a video 200% cause the other half to receive 0%?

[unskinnyboy]

The document you are referring to is old, quite old - last updated on December 30, 2004.

1. Is the weight option still bugged? No.


2. The weight option goes above one, it actually goes to two, meaning you can get 200% of your total bitrate. What?A weight of 2.00, or 200% means, Xvid would allocate double the bitrate to that zone, than what it would have normally allocated. Of course, this means taking some bitrate away from the rest of the encode.


3. There is no documentation anywhere on what the different quantization levels do (except for math formulas), however i set it at one halfway through my video, and the first half was a smeary mess and the second half was sharp and blocky. The only info i can find on quantization involves it being set to 1-3, but nowhere does anyone mention why there are 30 levels of it, or why GUI's like automkv like to set it at 20. Levels are 1-31, and you would find plenty of threads on this topic. Just search. I find it hard to believe that AutoMKV uses a default of 20 for Xvid. Most likely, it might be for x264, which would makes sense. That would be roughly equal to an Xvid quantizer value between 2 & 3.


4. If i allocate 15% of my total bitrate to half of a video, does the other half get 115%? Does giving one half of a video 200% cause the other half to receive 0%?Try it.