As a side note, that use of percentages for the bit rate is a side effect of JAWS because the control used to set the bit rate is a slider. I do not know what the "under the hood" issues are with making a slider actually announce what gets displayed as you slide it, rather than always using percentages, but JAWS has been using the percentage convention for a very long time now for a lot of things that are not percentages. In this particular case with bit rate:
0% is 128 Kb per second
33% is 192
66% is 256
and 100% is 320
As far as I'm concerned, if it were at all possible, JAWS or any screen reader should announce the value "being slid" not how far along the slider range you are unless that's actually what's pertinent.
Brian - Windows 10 Home, 64-Bit, Version 1703, Build 15063 (dot level on request - it changes too often to keep in signature)