Unable to specify bitrate for output file

[creeve4]

What is the correct syntax for specifying the bitrate for the output file?

It should be: "-b:a value" or "b value" or "ab value" depending on the encoder used.

I have tried the following, all of which throw errors:

1. monkeyplug -a "-b:a 256k"
2. monkeyplug -a "b:a 256k"
3. monkeyplug -a "a 256k"
4. monkeyplug -a "ab 256k"
5. monkeyplug -a "a 256"
6. monkeyplug -a "ab 256"