From 3c20057d0cbbbed453a692d4dd4589d865808024 Mon Sep 17 00:00:00 2001
From: Liliana Marie Prikler <liliana.prikler@gmail.com>
Date: Sat, 29 Jan 2022 10:44:44 +0100
Subject: [PATCH] Add pkg-config fallback for locating ffmpeg.

Audacity >=3.1.0 no longer links against ffmpeg, but instead dynamically loads
it.  This dynamic loading mechanism fails to properly locate libraries outside
of LD_LIBRARY_PATH.

See <https://issues.guix.gnu.org/53591>.
---
 libraries/lib-ffmpeg-support/CMakeLists.txt      |  8 ++++++++
 libraries/lib-ffmpeg-support/FFmpegFunctions.cpp | 12 ++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/libraries/lib-ffmpeg-support/CMakeLists.txt b/libraries/lib-ffmpeg-support/CMakeLists.txt
index 8c5f06d7c..00810e4d0 100644
--- a/libraries/lib-ffmpeg-support/CMakeLists.txt
+++ b/libraries/lib-ffmpeg-support/CMakeLists.txt
@@ -1,5 +1,7 @@
 
 if (${_OPT}use_ffmpeg)
+   pkg_check_modules(FFMPEG libavcodec libavformat libavutil)
+
    set( SOURCES
       FFmpegTypes.h
 
@@ -100,6 +102,12 @@ if (${_OPT}use_ffmpeg)
       list(APPEND DEFINITIONS PRIVATE _DARWIN_C_SOURCE )
    endif()
 
+   if (FFMPEG_FOUND)
+      pkg_get_variable(LIBAVCODEC_LIBDIR libavcodec libdir)
+      list(APPEND DEFINITIONS PRIVATE
+                  "-DFFMPEG_PC_LIBDIR=\"${LIBAVCODEC_LIBDIR}\"")
+   endif()
+
    audacity_library( lib-ffmpeg-support "${SOURCES}" "${LIBRARIES}"
       "${DEFINITIONS}" ""
    )
diff --git a/libraries/lib-ffmpeg-support/FFmpegFunctions.cpp b/libraries/lib-ffmpeg-support/FFmpegFunctions.cpp
index 66d085a0b..4eeb4aed3 100644
--- a/libraries/lib-ffmpeg-support/FFmpegFunctions.cpp
+++ b/libraries/lib-ffmpeg-support/FFmpegFunctions.cpp
@@ -238,6 +238,18 @@ struct FFmpegFunctions::Private final
       if (library->IsLoaded())
          return library;
 
+#if defined(FFMPEG_PC_LIBDIR)
+      {
+         static const wxString libdir{FFMPEG_PC_LIBDIR};
+         const wxString fullName = wxFileName(libdir, libraryName).GetFullPath();
+
+         auto library = std::make_shared<wxDynamicLibrary>(fullName);
+
+         if (library->IsLoaded())
+            return library;
+      }
+#endif
+
       // Loading has failed.
       // wxLogSysError doesn't report errors correctly on *NIX
 #if defined(_WIN32)
-- 
2.34.0

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