The Nero AAC Encoder is a fully functional, high quality, commandline LC and HE AAC encoder and is free for non-commercial use. There are versions for both Windows and Linux (x86)

./neroAacEnc [options] -if <input-file> -of <output-file>

<input-file>
Path to source file to encode.
The file must be in Microsoft WAV format and contain PCM data.
Specify - to encode from stdin.
Note that multiple input files can be specified, they will be encoded together into a single output file with chapter marks indicating source file divisions.
<output-file>
Path to output file to encode to, in MP4 format.

NeroAacEnc部分参数介绍:

Quality/bitrate control

-br <number>
Specifies "target bitrate" mode. (ABR)
<number> is target bitrate in bits per second ranging from 8000 to 400000.

Multipass encoding

-2pass
Enables two-pass encoding mode.
Note that two-pass mode requires a physical file as input, rather than stdin.
Using two-pass encoding is not recommended when using VBR.

Q: What is the -2pass option good for?
A: Two pass encoding ensures that the output quality is constant (like VBR) while also ensuring that a specified output bitrate is achieved (like CBR).

Two pass使指定输出码率情况下编码输出的质量更稳定。

Advanced features / troubleshooting

-ignorelength
Ignores length signaled by WAV headers of input file. Useful for certain frontends using stdin.
-lc
Forces use of LC AAC profile (HE features disabled). (LC = Low Complexity)
-he
Forces use of HE AAC profile (HEv2 features disabled). (HE = High Efficiency)
-hev2
Forces use of HEv2 AAC profile

使用举例:

./neroAacEnc -ignorelength -lc -br 128000 -2pass -if /data/input.wav -of /data/output.mp4  &> /dev/null

References:

https://www.audiocoding.com/nero_aacenc.html
http://wiki.hydrogenaud.io/index.php?title=Nero_AAC