Strange behaviour when setting the quality for AAC (avcodec) in Handbrake

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damian101
Posts: 8
Joined: Wed Apr 18, 2018 9:06 pm

Strange behaviour when setting the quality for AAC (avcodec) in Handbrake

Post by damian101 »

Description of problem or question:
I always liked the option to set the quality and not the average bitrate for Audio encoding because you don't have to think about what bitrate you should chose for a different amount of channels. So instead of setting the bitrate for AAC (avcodec) in Handbrake I preferred to set the quality (I usually took quality 4 because of some testing I did back then). But as I wanted to know how the bitrate per channel changed with different amounts of channels, I made some testing and the results where quite strange:
I took the short film Intel with the surround in lossless FLAC 5.1 surround and encoded the audio in a lot of different quality and channel settings and measured the overall bitrate of the Audio stream with MediaInfo:

ch:6 ch:2 ch:1
q:5 734 kb/s 453 kb/s 230 kb/s
q:4 611 kb/s 453 kb/s 230 kb/s
q:3 478 kb/s 453 kb/s 230 kb/s
q:2 333 kb/s 353 kb/s 230 kb/s
q:1 173 kb/s 183 kb/s 182 kb/s

How can some of these things be? For quality settings 1 and 2, 6 channels take up less space than 2 channels! That means that the bitrate per channel is more than 3 times higher at the same quality? And the movie has real surround sound, I tested it, so no channel is identical to another.
Some other things are strange as well like that the bitrate does not always change with rising quality... Any explanation?

Steps to reproduce the problem (If Applicable):




HandBrake version (e.g., 1.0.0):
HandBrake Nightly 20180227205614-369b4f6-master 64bit



Operating system and version (e.g., Ubuntu 16.04 LTS, macOS 10.13 High Sierra, Windows 10 Creators Update):
Windows 10 Pro 1709



HandBrake Activity Log ***required*** (see How-to get an activity log)

Code: Select all

HandBrake Nightly 20180227205614-369b4f6-master (2018030501) - 64bit
OS: Microsoft Windows NT 10.0.16299.0 - 64bit
CPU: Intel(R) Core(TM) i7-3720QM CPU @ 2.60GHz
Ram: 16202 MB, 
GPU Information:
  NVIDIA Quadro K1000M - 23.21.13.9133
  Intel(R) HD Graphics 4000 - 10.18.10.4358
Screen: 1920x1080
Temp Dir: C:\Users\damia\AppData\Local\Temp\
Install Dir: C:\Program Files\HandBrake Nightly
Data Dir: C:\Users\damia\AppData\Roaming\HandBrake Team\HandBrake\1.1.0.0

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nawoa
Posts: 30
Joined: Tue Dec 21, 2010 5:29 pm

Re: Strange behaviour when setting the quality for AAC (avcodec) in Handbrake

Post by nawoa »

I came here to report the same thing. AAC "quality" encoding seems totally broken. Encode the same video with various different AAC "quality" settings and observe the output file sizes. I don't remember exactly what my results were from my testing last week, but IIRC beyond quality 3 or 4 it's the exact same file size.

Bitrate is also unexpectedly high; for stereo I would think quality 1 might be like 80 kbps average, 2 might be 96, 3 might be 112, 4 128, 5 160, 6 192, 7 224, 8 256, 9 288, 10 320... or something like this. Instead 1 is 200+ kbps and it just goes higher.
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