Make avdevice library optional again

[dimula73]

It is not used by avformat when performing playback via SDL2, the only thing it does is initializing avdevice and not using it later.

This is a follow-up of the previous rejected MR: #1239

[ddennedy]

working for me with avdevice included 👍

[jlskuz]

Making the dependency optional is in principle fine for me, but I would prefer to have it explicitly managed with a WITH_AVDEVICE switch. I know we still have this implicit behavior in other places (like for ladaspa.h) still, but my goal would be to have them all controlled explicitly in the future. See #1115 for more context.

[dimula73]

Hi, @jlskuz!

I have applied your USE_AVDEVICE suggestions. Does this patch need any other changes before it could be merged?

[ddennedy]

@jlskuz prefers that options be explicit instead of discovered by what is available. For example, for the jackrack module that originally provided only ladspa we added in the top level CMakeLists.txt

option(USE_LV2 "Enable LV2 features" ON)  
option(USE_VST2 "Enable LV2 features" ON)

I think the same is desired for avformat:

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36c8d82f..ea7745f3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -20,6 +20,7 @@ option(CLANG_FORMAT "Enable Clang Format" ON)
 option(BUILD_TESTS_WITH_QT6 "Build test against Qt 6" ON)

 option(MOD_AVFORMAT "Enable avformat module" ON)
+option(USE_AVDEVICE "Integrate FFmpeg libavdevice for capture" ON)
 option(MOD_DECKLINK "Enable DeckLink module" ON)
 option(MOD_FREI0R "Enable Frei0r module" ON)
 option(MOD_GDK "Enable GDK module" ON)
diff --git a/src/modules/avformat/CMakeLists.txt b/src/modules/avformat/CMakeLists.txt
index aebb4637..3b197daa 100644
--- a/src/modules/avformat/CMakeLists.txt
+++ b/src/modules/avformat/CMakeLists.txt
@@ -51,7 +51,7 @@ if(WIN32)
   endif()
 endif()

-if(AVDEVICE_FOUND)
+if(USE_AVDEVICE AND AVDEVICE_FOUND)
   target_compile_definitions(mltavformat PRIVATE USE_AVDEVICE)
 endif()

Beyond that, I tested this branch again, and what you have still works for me.