m4a audio format unable to reduce bitrate from 112k could this change be made?

[mhussaincov]

hi there, when i choose the m4a audio format I can't change the bit-rate from 112k to another one say 32 kbps or 64 kbps. could it be made that the bit-rate, audio frequency could be changeable? also unable to change the audio channels from 2 to one could this option be enabled? thanks, Majid Hussain