FFmpeg: Move av/swresample decision into CMake (#693)

* FFmpeg: Move av/swresample decision into CMake

By making the determination as to which resampling library to use
in the `src/CMakeLists.txt` code, only that library needs to be
linked with libopenshot (and not the unused one), plus the choice
can be displayed in the FeatureSummary at configure time.

* src/CMakeLists: Fix FFmpeg hwaccel version check

src/CMakeLists.txt

@@ -294,12 +294,17 @@ find_package(FFmpeg REQUIRED
 )
 
 set(all_comps avcodec avformat avutil swscale)
-if(TARGET FFmpeg::swresample)
-  list(APPEND all_comps swresample)
+set(version_comps avcodec avformat avutil)
+
+# Pick a resampler.  Prefer swresample if possible
+if(TARGET FFmpeg::swresample AND ${FFmpeg_avformat_VERSION} VERSION_GREATER "57.0.0")
+  set(resample_lib swresample)
+  set(USE_SW TRUE)
 else()
-  list(APPEND all_comps avresample)
+  set(resample_lib avresample)
+  set(USE_SW FALSE)
 endif()
-set(version_comps avcodec avformat avutil)
+list(APPEND all_comps ${resample_lib})
 
 foreach(ff_comp IN LISTS all_comps)
   if(TARGET FFmpeg::${ff_comp})
@@ -313,9 +318,15 @@ foreach(ff_comp IN LISTS all_comps)
   endif()
 endforeach()
 
+# Indicate which resampler we linked with, and set a config header flag
+add_feature_info("FFmpeg ${resample_lib}" TRUE "Audio resampling uses ${resample_lib}")
+# Set the appropriate flag in OpenShotVersion.h
+set(FFMPEG_USE_SWRESAMPLE ${USE_SW} CACHE BOOL "libswresample used for audio resampling" FORCE)
+mark_as_advanced(FFMPEG_USE_SWRESAMPLE)
+
 # Version check for hardware-acceleration code
 if(USE_HW_ACCEL AND FFmpeg_avcodec_VERSION)
-  if(${FFmpeg_avcodec_VERSION} VERSION_GREATER "57.107.100")
+  if(${FFmpeg_avcodec_VERSION} VERSION_GREATER "57.106")
     set(HAVE_HW_ACCEL TRUE)
   endif()
 endif()