divx3/divx5/xvid/... - vbr,sbc???

[E-Male]

can someone explain to me how good the variouse codecs do the vbr calculating and how good and how much they change the bitrate of the frames and accordign to what? or do some codecs work cbr only? and how does sbc differ from or add to vbr?

thx in advance
cu
e-male

[DJ Bobo]

sbc = 2-pass vbr

They are all good in vbr calculating :D
For DivX5, increase the RC averaging period to the half of the total number of the frames to get optimal vbr fluctuation. Don't ask me why, if you wanna ask, ask Gej!

[Narler]

Hi E-Male,

Not sure if this will be of any benefit to you or not, but I made a web page of some codec and encoder tests I performed just recently.

I mainly did these tests for my own benefit, so I can work out what options best suit my needs, so I haven't covered all options with each codec. The main things I was looking for.. Encoding Speed, Filesize created, and Image Quality.

I've compared Div-x version 4.01 with version 5.0.0, version 5.0.2, and version 5.0.2 PRO

Another aspect of Div-x encoding is the difference between Constant Bit Rate, or Quality Based encoding methods. So I've done some comparisons between using Quality Based settings, and a few Constant Bit Rates.

The other very popular encoding format is MPEG, so I've done some comparisons between Constant Bit Rate MPEG 1 and Constant Bit Rate MPEG 2. With Mpeg I've also compared 3 MPEG encoding programs.

As most shows here are now broadcast in wide screen format, I've covered frame size cropping to see if it influences filesizes and encoding times.

Each test I've displayed the encoding times, so you can see which codec and encoder was the most efficient.

Lastly I've captured a some frames from each test file, so that quality can be compared between encoding settings.
(you have to take into account that i've used jpeg compression to help keep the web space requirements down)

You can access the codec test results directly Using This Link:

The Codec and Encoder Test Results (http://home.iprimus.com.au/narler/codec.htm)

You can access the codec frame quality comparison page directly Using This Link:

The Frames Comparison Page (http://www.aussievideosearch.com/codec-frames.htm)
(*Warning* this page is about 2.5MB in size including ALL images)

As the codec test results page is quite long I have setup a quick access menu in the left frame, which you won't see from the above links, so if you wish to use this then goto my main page, click on INFORMATION, then click on CODEC TEST

This is my Main Web Page (http://home.iprimus.com.au/narler/)

Hope you find my results of some benefit.

cya
Narler

[theReal]

I noticed that some of your cropped pictures still have a small black bar (only one or two pixels wide) at the top and/or at the bottom.

Make another file size comparison where you crop these remaining black pixels off and keep the video height divisible by 8 - you'll see that this makes a big difference for compressibility...

[Teegedeck]

A variable bitrate is the effect if all frames of a video are treated alike by a codec. It means, a shot of a white wall undergoes the same details-removal as a scene in a crowded street. In DiX4/5 or XviD you reach this effect by encoding at a constant quantizer or quality. This kind of perfect VBR usually allows for no controll of either bitrate or total filesize of your encoding in the end.

Constant Bitrate (CBR) would mean, each frame is allowed to have the same size, and it would be reached by removing lots of details from the crowded-street-scene and very little from the shot of the white wall. That would look really, really terrible. Thus, the 'CBR'-modes of DivX4/5 are not really CBR but try to controll filesize/bitrate by removing more details from (preferably complex) frames only whenever the algorhythms at work realize that they're not gonna reach the average bitrate/filesize that the user wanted. The longer the averaging period, the longer the encoder waits before taking harsh measures for keeping filesize, thus you have less controll over the final filsize/average bitrate.

The best comprosmise between quality and size is always a two-pass-mode. It's what Nando called Smart Bitrate Controll (SBC) when he developed Nandub. After the first pass, the codec/encoder knows where it can most effectively and least obstrusively compress stronger.

I wrote in a bit of a hurry, so please bear with me.