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

Question

When I use ffmpeg to convert an audiofile with the option

-acodec libfaac -ab 192k 

and use

ffmpeg -i 

on that file afterwards to get the audio file information, it tells me

bitrate: 152 kb/s

Why ist this? Do I miss something here? If I want to convert a file with a bitrate of 192kb it should give me 192 kbit after the conversion, shouldn't it?

Or: How do I get the 192 kbit rate then?

Answer 1

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.