ffmpeg options: -acodec libfaac -ab 192k produce 150kbit files?

I can't provide any further explanation, but several places (e.g. [1]) mention:

Note that the maximum average bit-rate (what -ab specifies in the context of libfaac) is 152 kbit/s. Setting this higher will be ignored and 152 kbit/s will be used.

There are now much better aac encoders for Linux such as NeroAacEnc or fdkaac but if you are still keen on using faac there is a patch that means faac can encode with a bitrate of 192k, and a great deal higher as well. Handbrake formerly used this patch and hosted it on their site but the developers have dropped faac support now, I now host the patch here:

http://www.andrews-corner.org/patches/A00-bitrates.patch

Patch Faac and then compile FFmpeg with --enable-libfaac and you can have high bitrate aac files with Faac. Here is a sample encode with the patched faac, encoding directly with faac:

andrew@skamandros~/media$ faac -b 192 -o test.m4a test.wav 
Freeware Advanced Audio Coder
FAAC 1.28

Average bitrate: 192 kbps
Quantization quality: 100
Bandwidth: 20872 Hz
Object type: Low Complexity(MPEG-4) + M/S
Container format: MPEG-4 File Format (MP4)
Encoding test.wav to test.m4a
   frame          | bitrate | elapsed/estim | play/CPU | ETA
11720/11720 (100%)|  192.0  |   21.7/21.7   |   12.52x | 0.0  

andrew@skamandros~/media$ 

And it works as well with FFmpeg. But there are definitely better aac encoders out now...

References:

• How can I rebuild the faac package to get mp4/m4a support and higher bitrates? An askubuntu guide to rebuilding the faac debian package to allow higher bitrates.