What is AutoGOP and Auto-AAC, and how does it relate to quality?

[BuddTX]

I tried searching, and did not come up with any answers, sorry.

OK, so I do know that AutoGOP automatically adjusts the compression on "group of pictures", and searching GOP gives me tons of info on what GOP is.

So I know that AutoGOP has something to do with the compression of video.

And Auto-AAC, the alternate.txt says:
# aBitrate=Bitrate to use for audio encoding, * = automatic (not allowed for iPod & iPad)

I am more familiar with LAME and MP3 encoding, so I am GUESSING that Auto-AAC is something like VBR (Variable Bit Rate)??

Reason for asking? I wanted to know how it relates to quality, as opposed to choosing one of the other MKV options.

I use BD-Rebuilder exclusively to make MKV's from Blu-Rays, DVD's, and while I keep the MKV files on a Hard Drive, I still want the optimal size vs quality output.

My thoughts were this, is this format my best choice for optimal quality vs size in creating an MKV file:
caption=MKV Container, NO_RESIZE, AutoGOP, Auto-AAC
vBitrate=2000
aBitrate=*
aType=1
vFormat=7
vKeyint=Auto
cType=1

My thinking is that no matter what my souce (Blu-Ray or DVD), I keep the optimal video, and let the programs figure out what is best.

I also use
ENCODE_QUALITY=4
in my INI file, cause I am anal!

Thanks for shedding light on this subject!

[BuddTX]

Anybody?

[radar]

I to would like to know peoples thoughts on the above...

[jdobbs]

AutoGOP modifies the distance between I frames (X264 setting --keyint) based upon the framerate. Generally it will give you a better balance of picture to output size by using a longer GOP (group of pictures). These longer GOPs are nice, but require memory/power on the side of the player and they put a large gap (10 seconds) between "landing points" when seeking. In the blu-ray player standard they are limited to about 1-2 seconds. They are also limited by specification on many other players (iPod, iPad, etc). Most of the MKV and MP4 files you see floating around on the internet use long GOPs.

AutoAAC looks at the number of audio channels and gives a bitrate that BD-RB thinks is most appropriate. For example, if AutoAAC were not selected and you set a fixed bitrate of 448Kbs -- and the source was stereo, you'd wasting a lot of space. If you set a bitrate of 192, and the source was 5.1, BD-RB would have no choice but to downmix to stereo. AutoAAC would avoid those situations. Again, though, there are players that you have to consider. For example, an iPad/iPhone's specs says it only accepts stereo AAC audio at no more than 160Kbs.