So in summary "Getting a build to work in a custom environment is not easy."

Andrew noted: "CFLAGS=-I/usr/include/ffmpeg as example from previous attempt."

So just FYI, I updated the manual to add the following in section 1.3.5 custom build of the Installation section as recommended by Andrew. I hope it might help in the future.

If you have a problem with libdpx (a wrapper of VPixx low-level library for Python),
resolve that by changing the conﬁgure line as shown to build without it:

./confgure --with-single-user --without-libdpx

If you have some of your thirdparty libraries installed in non-standard locations or
if you want to use a speciﬁc version, consider setting CFLAGS=-I/<path> to pass
that location to the compiler so it knows where to ﬁnd it.