videoconvert: add an ffmpeg based video converter

To activate:

PIPEWIRE_PROPS='{ video.adapt.converter = video.convert.ffmpeg }' build/src/examples/video-play

This makes it possible to start firefox with mjpg capture and then
video-play and it will decode the mjpeg transparently. Works for other
incompatible video formats as well, as long as they can be mmapped.

Ideally this should use something GPU accelerated and this is what the
vulkan converter will do.

meson.build

@@ -310,7 +310,8 @@ ffmpeg = get_option('ffmpeg')
 if pw_cat_ffmpeg.allowed() or ffmpeg.allowed()
   avcodec_dep = dependency('libavcodec', required: pw_cat_ffmpeg.enabled() or ffmpeg.enabled())
   avformat_dep = dependency('libavformat', required: pw_cat_ffmpeg.enabled())
-  avutil_dep = dependency('libavutil', required: pw_cat_ffmpeg.enabled())
+  avutil_dep = dependency('libavutil', required: pw_cat_ffmpeg.enabled() or ffmpeg.enabled())
+  swscale_dep = dependency('libswscale', required: pw_cat_ffmpeg.enabled() or ffmpeg.enabled())
 else
   avcodec_dep = dependency('', required: false)
 endif

spa/plugins/videoconvert/meson.build

@@ -4,13 +4,23 @@ videoconvert_sources = [
   'plugin.c'
 ]
 
-simd_cargs = []
-simd_dependencies = []
+extra_cargs = []
+extra_dependencies = []
+
+if avcodec_dep.found() and avutil_dep.found() and swscale_dep.found()
+  videoconvert_ffmpeg = static_library('videoconvert_fmmpeg',
+    ['videoconvert-ffmpeg.c' ],
+    dependencies : [ spa_dep, avcodec_dep, avutil_dep, swscale_dep ],
+    install : false
+    )
+  extra_cargs += '-D HAVE_VIDEOCONVERT_FFMPEG'
+  extra_dependencies += videoconvert_ffmpeg
+endif
 
 videoconvertlib = shared_library('spa-videoconvert',
   videoconvert_sources,
-  c_args : simd_cargs,
+  c_args : extra_cargs,
   dependencies : [ spa_dep, mathlib ],
-  link_with : simd_dependencies,
+  link_with : extra_dependencies,
   install : true,
   install_dir : spa_plugindir / 'videoconvert')

spa/plugins/videoconvert/plugin.c

@@ -9,6 +9,9 @@
 
 extern const struct spa_handle_factory spa_videoadapter_factory;
 extern const struct spa_handle_factory spa_videoconvert_dummy_factory;
+#if HAVE_VIDEOCONVERT_FFMPEG
+extern const struct spa_handle_factory spa_videoconvert_ffmpeg_factory;
+#endif
 
 SPA_LOG_TOPIC_ENUM_DEFINE_REGISTERED;
 
@@ -25,6 +28,11 @@ int spa_handle_factory_enum(const struct spa_handle_factory **factory, uint32_t
 	case 1:
 		*factory = &spa_videoconvert_dummy_factory;
 		break;
+#if HAVE_VIDEOCONVERT_FFMPEG
+	case 2:
+		*factory = &spa_videoconvert_ffmpeg_factory;
+		break;
+#endif
 	default:
 		return 0;
 	}