Av Bit Rate v Constant Quality

[Rinc ewindwiz]

I was reading the stuff in the doc about this (https://handbrake.fr/docs/en/latest/tec ... s-abr.html) and am confused - perhaps someone can help?

Target Bitrate
Surely there is no real difference between varying the Quality (different RF) and varying the bitrate. You can specify your most important constraint (quality or size) and in both cases the encoder varies the bitrate frame by frame to give the 'best' result. 2 pass allows it to optimise this over the entire video.

So the comments under ' . . . two modes of encoding . ." are just fine but what comes next seems misleading:

Benefits: No need to do 2 pass encoding: Not True. You do not need 2 pass encoding with average bit rate (certainly Handbrake allows this) but doing so allows the encoder to optimise the use of bitrate over the entire video.

Constant Quality can produce same quality as 2-pass encode: Obviously true, but next to the previous sentence it implies you can do it in half the time AND for the same bit rate (otherwise where is the advantage?) and surely that cannot be true?

Reduced file sizes: The statement is true but it is also true of Average Bit rate encoding and especially true of 2 pass where information collected from the first pass allows the encoder to 'optimise' the allocation of bit rate across the entire movie thus giving best quality for a given bit rate (or best file size for a given quality)

Output file sizes is all true but also true of Av Bit Rate where you dont know what the quality will be but do know the file size. 2 pass encoding allows the encoder to optimise this

Personally I find that the differences in quality (for a given bit rate) are rarely noticeable and being able to fix the file size is much more useful

Just my 10c

[mduell]

You need 2 pass with an ABR target to achieve a bitrate distribution equivalent to what CQ produces.

CQ in a single pass produces the same output that ABR would produce with the same bitrate target in 2 passes.

Reduced file size is because people will set their ABR target based on a worst case (grainy, high motion, etc movies), and waste a lot of bits on simpler/stiller content.

[rollin_eng]

If you think of it like this:

CQ sacrifices known size for quality.

ABR sacrifices known quality for size.

If quality is more important select CQ, if size is more important select ABR.

[mduell]

CQ sacrifices known size for quality.

ABR sacrifices known quality for size.

ABR also takes longer (2 pass) to hit the same quality at the same bitrate.