That seems to be the right approach, however I doubt that 0x12c is the right pid. Maybe you should get a copy of the TS from streamdev (just use wget on the streamdev url) and then analyze what you can identify there. I think it should be 0x11 for MPEG4-Audio...
You could also have a look at streamdev's pid filtering since obviously this is already working as expected.
I just did this for you and it seems 0x11 would indeed match what you're looking for, looking at streamdev/server/livestreamer.c:
case 0x11: // ISO/IEC 14496-3 Audio with LATM transport syntax
Best regards, Christian