cmake: check for ffmpeg >= 4.0.4

Check for the specific `ffmpeg` lib versions in `ffmpeg` `4.0.4` "Wu",

Do not pass `-DENABLE_FFMPEG=OFF` to the xenial travis job, as this is
detected automatically now.

Add a note about the required ffmpeg version to `README.md`.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

.travis.yml

@@ -32,8 +32,7 @@ matrix:
           script:
               - mkdir build
               - cd build
-# ffmpeg currently broken on xenial
-              - cmake .. -DENABLE_SDL=ON -DENABLE_FFMPEG=OFF
+              - cmake .. -DENABLE_SDL=ON
               - make -j2
 # xvfb fails on xenial too
 #              - xvfb-run ./visualboyadvance-m --help

CMakeLists.txt

@@ -120,13 +120,17 @@ set(FFMPEG_DEFAULT OFF)
 
 find_package(PkgConfig)
 
+set(FFMPEG_LIBS_LIST libavcodec>=58.18.100 libavformat>=58.12.100 libswscale>=5.1.100 libavutil>=56.14.100 libswresample>=3.1.100)
+
 if(PKGCONFIG_FOUND)
     set(FFMPEG_DEFAULT ON)
 
-    foreach(ffmpeg_lib libavcodec libavformat libswscale libavutil libswresample)
-        pkg_check_modules(FFMPEG_LIB_${ffmpeg_lib} ${ffmpeg_lib} QUIET)
+    foreach(ffmpeg_lib ${FFMPEG_LIBS_LIST})
+        string(REGEX REPLACE ">=.*" "" ffmpeg_lib_name ${ffmpeg_lib})
 
-        if(NOT FFMPEG_LIB_${ffmpeg_lib}_FOUND)
+        pkg_check_modules(FFMPEG_LIB_${ffmpeg_lib_name} ${ffmpeg_lib} QUIET)
+
+        if(NOT FFMPEG_LIB_${ffmpeg_lib_name}_FOUND)
             set(FFMPEG_DEFAULT OFF)
             break()
         endif()
@@ -290,7 +294,7 @@ set(
 if(ENABLE_FFMPEG)
     find_package(PkgConfig REQUIRED)
 
-    pkg_check_modules(FFMPEG REQUIRED libavcodec libavformat libswscale libavutil libswresample)
+    pkg_check_modules(FFMPEG REQUIRED ${FFMPEG_LIBS_LIST})
 
     if(FFMPEG_STATIC)
         set(FFMPEG_LIBRARIES ${FFMPEG_STATIC_LIBRARIES})

README.md

@@ -111,7 +111,7 @@ And the following development libraries:
 
 - [zlib](https://zlib.net/) (required)
 - [mesa](https://mesa3d.org/) (if using X11 or any OpenGL otherwise)
-- [ffmpeg](https://ffmpeg.org/) (optional, for game recording)
+- [ffmpeg](https://ffmpeg.org/) (optional, at least version `4.0.4`, for game recording)
 - [gettext](https://www.gnu.org/software/gettext/) and gettext-tools (optional, with ENABLE_NLS)
 - [libpng](http://www.libpng.org/pub/png/libpng.html) (required)
 - [SDL2](https://www.libsdl.org/) (required)