FFmpeg itself is composed of several subcomponents that can be used individually, and outside of FFmpeg, for instance in your own program. These are

• libavformat which contains muxer information and capabilities.
• libavcodec which contains all the (built-in) video encoding and decoding codecs that FFmpeg contains.
• libswscale contains the (raw pixel) format conversions, and also high speed/assembly optimized versions of certain scaling routines.
• libavfilter contains the filters FFmpeg contains, like adjusting audio sample rate, etc.* libavutil ??
• libavdevice contains interfaces for working with "local devices" for instance webcams in windows, line-in audio in linux, etc.
• libpostproc ??

Getting started

There is not much "web based" official documentation for using these libraries.

Check  doc/examples, also doxygen documentation is fairly complete and should work as reference (example: the libavformat doxygen).

Here also are some notes that may be helpful: