Help assembling libav

Looking to replace ffmpeg with libav to see if that solves my ffmpeg issue.

I am trying to assemble libav.

I do not understand this statement

'configure' can be launched from a directory different from the Libav
sources to build the objects out of tree. To do this, use an absolute
path when launching 'configure', e.g. '/libavdir/libav/configure'.

This is probably not mandatory so you can just write ./configure inside the source directory and all should be well. If it fails, then you can do a mkdir build and then cd build and then ../configure.

I've seen building "out of tree" become more widespread with modern versions of software. The idea is that, after you've built your software in a different directory, you may simply remove that directory to return the software source directory to a "clean" state. It isn't too useful unless you're planning to rebuild the software a lot and cannot endure the time it takes to untar it .