Couldn't agree more on the C API. The time I had to use it was a nightmare. There's almost no documentation, and the interface changes so often it's nearly impossible to find working sample code.
This should be deployed with any new fresh ffmpeg install.
The filtering code is still unstable due to what's explained in the blog post...
To be honest, the biggest problem I had was that searches would return too many out of date code snippets and sample code on other sites that didn't match the exact version I was using, so it wouldn't work for me.
Other than that, once I got it working, it was awesome.