FFmpeg currently uses a custom build system, this text attempts to document

 some of its obscure features and options.
 

 Makefile variables:

 V
     Disable the default terse mode, the full command issued by make and its
     output will be shown on the screen.

 DBG
     Preprocess x86 external assembler files to a .dbg.asm file in the object
     directory, which then gets compiled. Helps developping those assembler
     files.
 

 DESTDIR
     Destination directory for the install targets, useful to prepare packages

     or install FFmpeg in cross-environments.

 GEN
     Set to ‘1’ to generate the missing or mismatched references.
 

 Makefile targets:

 all
     Default target, builds all the libraries and the executables.

 fate
     Run the fate test suite, note you must have installed it
 
 fate-list
     Will list all fate/regression test targets
 

 install
     Install headers, libraries and programs.

 examples
     Build all examples located in doc/examples.
 

 libavformat/output-example
     Build the libavformat basic example.

 libavcodec/api-example
     Build the libavcodec basic example.

 libswscale/swscale-test
     Build the swscale self-test (useful also as example).

 config
     Reconfigure the project with current configuration.
 

 
 Useful standard make commands:
 make -t <target>
     Touch all files that otherwise would be build, this is useful to reduce
     unneeded rebuilding when changing headers, but note you must force rebuilds
     of files that actually need it by hand then.
 
 make -j<num>
     rebuild with multiple jobs at the same time. Faster on multi processor systems
 
 make -k
     continue build in case of errors, this is useful for the regression tests
     sometimes but note it will still not run all reg tests.