differences between single pass and 2-pass target bitrate encoding?

[Luminaria]

i need to to a cbr encode at about 1600-1700kbps and was wondering if there is much of a difference between the 1-pass target bitrate and the 2-pass target bitrate encoding methods. thanks.

[b00zed]

If you're doing CBR encoding then 2-pass is unnecessary.

If you meant to type VBR then yes, 2-pass is useful as it allows you to hit the target bitrate with much more accuracy. Single pass VBR has to make various assumptions regarding the complexity of the video etc, in other words it doesn't have all the information it needs to evenly distribute the bits. That's where the first pass of a 2-pass encode job comes in handy, the encoder then knows exactly how complex and/or compressible the video is, and can distribute the bits to where they're needed with confidence.

[sysKin]

Short explaination, might help:

- single pass CBR keeps bitrate but fluctuates quality (very badly)
- single pass constant quantizer keeps constant quality at unpredictable filesize
- two-pass hits bitrate *and* keeps quality constant

:)

[Didée]

Originally posted by sysKin
[B] - single pass constant quantizer keeps constant quality at unpredictable filesize

There is jonny's enc (http://forum.doom9.org/showthread.php?s=&threadid=50714&highlight=enc) tool that - amongst other features - does a very good job at filesize prediction through short encodes similar to a compressability check.

What I sometimes like to do is to do a filesize prediction with enc, to get e.g. a target quantizer of 4.7 (high BR matrix), and then do a 1-pass CBR with quants limited to [4,5].

- Didée

[sysKin]

Originally posted by Didée
There is jonny's enc (http://forum.doom9.org/showthread.php?s=&threadid=50714&highlight=enc) tool that - amongst other features - does a very good job at filesize prediction through short encodes similar to a compressability check.

What I sometimes like to do is to do a filesize prediction with enc, to get e.g. a target quantizer of 4.7 (high BR matrix), and then do a 1-pass CBR with quants limited to [4,5].

- Didée Now THAT is what I call a super-hyper-fast 1st pass.
:D