iTunes AAC Encoding

Like Lisa Simpson, maybe I'm the answer to a question nobody asked...
I was curious what the "VBR Encoding" option was in iTunes for windows (Prefs->Advanced->Impoting->AAC Encoder)

iTunes can only access ABR and VBR_Constrained. ABR is the default. Checking VBR sets VBR_Constrained mode. So use that for best quality for your rips.


Apple AAC encoder offers four encoding modes:
Constant Bit Rate (CBR) -- Recommended for live streaming --
This mode achieves a constant target bit rate and is completely compliant to the CBR mode specified in the MPEG-4 standard.

Average Bit Rate (ABR) - Default Mode
-- Recommended for controlling file size --
A target bit rate is achieved over a long term average (typically after the first few seconds of encoding). This mode provides almost best global quality while still being able to strictly control the resulting file size and with less complexity than the CBR mode.

Variable Bit Rate (VBR)
-- Recommended for controlling the audio quality --
The audio signal is encoded with constant (and settable) quality and virtually no bit rate constraints. This is the best mode to achieve consistent audio quality across many files with the smallest file size to achieve that quality. It also has the lowest complexity of all the encoding modes.

Variable Bit Rate But Constrained (VBR_Constrained)
-- Recommended as a compromise between VBR and ABR --
This mode is similar to VBR but limits the average bit rate variation. The lower limit is the user-selected bit rate. Higher bit rate is adapted for difficult tracks and can generate up to 10% larger files than the ABR mode.