openscenegraph: FTBFS with ffmpeg 5.0

See also: https://github.com/openscenegraph/OpenSceneGraph/issues/1111
Imported from Debian bug http://bugs.debian.org/1004634:

openscenegraph FTBFS with ffmpeg 5.0 (available in experimental):
| [ 40%] Building CXX object src/osgPlugins/freetype/CMakeFiles/osgdb_freetype.dir/ReaderWriterFreeType.cpp.o
| cd /<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/src/osgPlugins/freetype && /usr/lib/ccache/c++ -Dosgdb_freetype_EXPORTS -I/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/include -I/<<PKGBUILDDIR>>/include -I/usr/include/freetype2 -g -O2 -ffile-prefix-map=/<<PKGBUILDDIR>>=. -fstack-protector-strong -Wformat -Werror=format-security -Wdate-time -D_FORTIFY_SOURCE=2 -Wdate-time -D_FORTIFY_SOURCE=2 -Wall -Wparentheses -Wno-long-long -Wno-import -pedantic -Wreturn-type -Wmissing-braces -Wunknown-pragmas -Wunused -Wmaybe-uninitialized -Wextra -Wshadow -Wno-misleading-indentation -O2 -g -DNDEBUG -fPIC -MD -MT src/osgPlugins/freetype/CMakeFiles/osgdb_freetype.dir/ReaderWriterFreeType.cpp.o -MF CMakeFiles/osgdb_freetype.dir/ReaderWriterFreeType.cpp.o.d -o CMakeFiles/osgdb_freetype.dir/ReaderWriterFreeType.cpp.o -c /<<PKGBUILDDIR>>/src/osgPlugins/freetype/ReaderWriterFreeType.cpp
| In file included from /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.hpp:10,
| from /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp:1:
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegPacket.hpp: In member function ‘void osgFFmpeg::FFmpegPacket::clear()’:
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegPacket.hpp:45:17: error: ‘av_free_packet’ was not declared in this scope; did you mean ‘av_new_packet’?
| 45 | av_free_packet(&packet);
| | ^~~~~~~~~~~~~~
| | av_new_packet
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp: In function ‘int osgFFmpeg::decode_audio(AVCodecContext*, int16_t*, int*, const uint8_t*, int, SwrContext*, int, int, AVSampleFormat)’:
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp:48:11: error: ‘avcodec_decode_audio4’ was not declared in this scope; did you mean ‘avcodec_decode_subtitle2’?
| 48 | ret = avcodec_decode_audio4(avctx, frame, &got_frame, &avpkt);
| | ^~~~~~~~~~~~~~~~~~~~~
| | avcodec_decode_subtitle2
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp:53:34: error: ‘av_frame_get_channels’ was not declared in this scope; did you mean ‘av_frame_get_buffer’?
| 53 | if (ret >= 0 && got_frame && av_frame_get_channels(frame)>0) {
| | ^~~~~~~~~~~~~~~~~~~~~
| | av_frame_get_buffer
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp: In member function ‘void osgFFmpeg::FFmpegDecoderAudio::open(AVStream*, osgFFmpeg::FFmpegParameters*)’:
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp:154:29: error: ‘AVStream’ {aka ‘struct AVStream’} has no member named ‘codec’
| 154 | m_context = stream->codec;
| | ^~~~~
| /<<PKGBUILDDIR>>/src/osgPlugins/ffmpeg/FFmpegDecoderAudio.cpp:217:55: error: invalid conversion from ‘const AVCodec*’ to ‘AVCodec*’ [-fpermissive]
| 217 | AVCodec * const p_codec = avcodec_find_decoder(m_context->codec_id);
| | ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
| | |
| | const AVCodec*
| make[3]: *** [src/osgPlugins/ffmpeg/CMakeFiles/osgdb_ffmpeg.dir/build.make:93: src/osgPlugins/ffmpeg/CMakeFiles/osgdb_ffmpeg.dir/FFmpegDecoderAudio.cpp.o] Error 1
| make[3]: Leaving directory '/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu'