Difference between Constant Bitrate and Constant Quality

[Slodown]

What`s the difference between those things

[KennyC]

Hi,

1. Constant Bitrate, you choose the bitrate and that's it, TMPGEnc really assumes you mean 100% Quality.

2. Constant Quality, you choose the Maximum Bitrate from 0 -> ?kbit/sec and also the Quality from 0 -> 100% (100% = BEST)

With my extensive testing, depending on your settings, the results will be the same/similar.

i.e.
CBR = 1150 will be the same as CQ = 100% + 1150
CBR = 1150 will be similar as CQ = 50% + 2300

It is really hard to compare, but a guide to me is the resulting filesize. Do both examples and compare the differences.



©.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·-- KennyC --·´¯`·.¸¸.·´¯`·.¸¸.·´¯`·.¸¸.©



<font size=-1>[ This Message was edited by: KennyC on 2001-12-25 05:22:55 ]</font>

[w00kiee]

constant bitrate (cbr) = non variable.. no matter wether the encoder needs all of the bitrate or not it uses it. on fast scenes you might get block distortion but that would depend on bitrate. 1150 (vcd) will tend to offer that distortion on really fast scenes. but thats vcd for ya.. most of the time it will look fine. at (2500 k/s at cbr) on slow/non-detailed scenes you waste the bandwidth. the p and b frames dont offer much change over the I (main most detailed frames) so they could be smaller but arent allowed to be by cbr setting

constant quality (cq) = a variable setting. it keeps the image quality constant or at least thats the goal. it uses your max bitrate on the scenes that need it and less if it can without hurting anything. where as other variables might be willing to sacrifice some block fixing in fast scenes if there arent enough slow scenes to steal bandwidth from. a cq encode could end up all at the max bitrate so kinda hard to calculate the final size in advance where as the 2pass vbr will average to your setting. cq is good if you say 'if i can save some bandwidth then goodie.. other wise nope' and vbr is 'i gotta fit this svcd onto x amount of disks and im willing to (possible) sacrifice a scene or 2 in quality do it' and cbr is 'i dont wanna wait forever to encode so ill take an inefficient encode and possible distortion in fast scenes'

[Slodown]

And what about Realtime constant bitrate and constant quality???

[w00kiee]

And what about Realtime constant bitrate and constant quality???

dont use them