Implementing '-async 1' in C code to correct out of sync audio

Question

I have built a segmenter that takes as input a h264 / AAC video and segments according to the HLS specification. The source code for it can be seen here: https://gist.github.com/cpnielsen/f36729c371aac0fe535d

It is implemented as a python extension, but the interesting parts are in the process_video() function. It makes use of the libav library (alternatively ffmpeg) to do the heavy lifting.

It works 95% of the time, but we have come upon some videos where it produces segments with audio out of sync. If I was using the command-line tool, I could simply add -async 1 to fix it, but how do I implement the same functionality in my C code?

I found a snippet of code in avconv_filter.c (for libav, not sure what the ffmpeg equivalent is) where they initiate the filter, but without any documentation it is hard to figure out how to do this outside the whole modular setup.

I just need to:

1. Initiate the correct filter
2. Apply it to the input (or output? not sure)
3. Know of any pitfalls when using the filter.

Any help is welcome; sample code, explanation of the filter, etc.