1 pass VBR vs CBR

[Buzzard]

What is the difference between encoding in a 1 pass VBR situation vs a CBR situation? In both you are making one pass unless in VBR you specify the creation of a VAF file first.

Do you use VBR when the bitrate is LOW? and CBR when you have enough bitrate ( maybe 2200+ or so ). In VBR I know that bit allocation within a frame depends on the complexity of the frame and the amount of motion in the scene - but doesn't CBR sort of do that in the Image Quality Setting ? - allocating bits according to complexity of the scene - more bits to complex parts as the Image Quality Setting number gets lower ?

I guess my main question is this - I find when I USE ENOUGH bitrate, say 2200 - 2400, then CBR looks as good or better than a 1 PASS VBR. I understand the need for multiple VBR passes at LOWER bitrates BUT Why should I even use VBR if my bitrate is high - say over 2200 ???? if CBR looks as good ( on a 53" screen ) and saves a lotta time ..

Buzzard

[delly01]

You're quite right, and this has been pointed out several times on the forum. However, it's often more convenient to use multi-pass-VBR to fit a movie onto two CD-Rs, and sacrifice the conversionspeed.

Anyway, I don't save time on CBR, because I start the conversion when I go to bed, and even 4x-VBR is finished when I come home from work the next day.

Remember: You transcode only once, but you will have to stand up from your couch a lot of times :-)

Bye,

Detlev

[markrb]

CBR vs VBR is a question of filesize vs video quality. A normal bitrate CBR encode can look no worse then a VBR encode using the same Max value as the CBR value. Bits is bits. However the question comes in what if I drop the CBR bitrate to fit the same number of CD's I can get with a VBR with a higher MAX value. This is where you see the difference. If a CBR encode will fit the same number of cd's and has the same value as the Max of the VBR encode there is really no reason to use VBR.

A VBR encode attempts to maintain a certain average, but is allowed to exceed this value on tough scenes until it hits the Max value, a CBR encode does not have the option.

However since a VBR encode does not keep the same number of bits on every scene the filesize will be smaller.

The more the passes of VBR the better the enocoder gets at deciding the correct allocation of bits.

Mark