media-video/ffmpeg: Allow building libffmpeg for Chromium via USE flag

Chromium is built from source and therefore can be built against the
system ffmpeg. Google Chrome already ships with support for
proprietary codecs and has libffmpeg.so built in.

Opera and Vivaldi, on the other hand, do not support proprietary
codecs and actively encourage you to replace the libffmpeg.so they
provide. Official instructions involve downloading the huge Chromium
tarball and building tons of baggage that you don't actually need,
despite the fact that libffmpeg.so is really just the main ffmpeg
libraries combined.

In order to build this, I felt it was worthwhile leveraging our
existing feature-rich ffmpeg package rather than duplicating it or
creating some poor imitation. This commit shows what little extra code
is required.

It would be possible to link to the regular libraries directly instead
of buildling additional copies if it weren't for the fact that these
browsers are usually built with -DFF_API_CONVERGENCE_DURATION=0,
making the ABI incompatible, at least until libavcodec hits 59.

That aside, all Chromium versions between 59 and 61 (maybe earlier?)
use the 55.57.57 ffmpeg ABI found in the 3.x series. Having these
browsers optionally RDEPEND on ffmpeg:0/55.57.57[chromium] should
therefore not be a problem for the time being. They simply need to
provide a symlink.

I have tested this with current versions of vivaldi, vivaldi-snapshot,
opera, opera-beta, and opera-developer. None were able to play videos
on news.bbc.co.uk without Flash until swapping in this library.

It has been noted that Vivaldi could potentially be built from
source. I may explore this possibility but I believe this change is
still useful, especially as some lack sufficient hardware to build
these browsers from source.

Package-Manager: Portage-2.3.6, Repoman-2.3.2

1 files changed, 45 insertions, 0 deletions

diff --git a/media-video/ffmpeg/files/chromium.patch b/media-video/ffmpeg/files/chromium.patch
new file mode 100644
index 000000000000..bc8b8d38698b
--- /dev/null
+++ b/media-video/ffmpeg/files/chromium.patch
@@ -0,0 +1,45 @@
+Allow libffmpeg to be built for Chromium-based browsers
+https://patchwork.ffmpeg.org/patch/4500/
+
+diff --git a/Makefile b/Makefile
+index 29870d7..1e267e7 100644
+--- a/Makefile
++++ b/Makefile
+@@ -65,6 +65,7 @@ all: all-yes
+ 
+ include $(SRC_PATH)/tools/Makefile
+ include $(SRC_PATH)/ffbuild/common.mak
++include $(SRC_PATH)/ffbuild/libffmpeg.mak
+ 
+ FF_EXTRALIBS := $(FFEXTRALIBS)
+ FF_DEP_LIBS  := $(DEP_LIBS)
+diff --git a/ffbuild/libffmpeg.mak b/ffbuild/libffmpeg.mak
+new file mode 100644
+index 0000000..992cf3c
+--- /dev/null
++++ b/ffbuild/libffmpeg.mak
+@@ -0,0 +1,21 @@
++LIBFFMPEG = $(SLIBPREF)ffmpeg$(SLIBSUF)
++LIBFFMPEG_LINK = $(LD) -shared -Wl,-soname,$(LIBFFMPEG) -Wl,-Bsymbolic -Wl,-z,now -Wl,-z,relro -Wl,-z,defs -Wl,--gc-sections $(LDFLAGS) $(LDLIBFLAGS) -o $(LIBFFMPEG)
++
++libffmpeg-: libavcodec/$(LIBPREF)avcodec$(LIBSUF) libavformat/$(LIBPREF)avformat$(LIBSUF) libavutil/$(LIBPREF)avutil$(LIBSUF) libswresample/$(LIBPREF)swresample$(LIBSUF)
++	$(LIBFFMPEG_LINK) -Wl,--whole-archive $^ -Wl,--no-whole-archive $(FFEXTRALIBS)
++
++libffmpeg-yes: libavcodec/$(SLIBPREF)avcodec$(SLIBSUF) libavformat/$(SLIBPREF)avformat$(SLIBSUF) libavutil/$(SLIBPREF)avutil$(SLIBSUF)
++	$(LIBFFMPEG_LINK) -Wl,--no-as-needed -lavcodec -lavformat -lavutil
++
++$(LIBFFMPEG): libffmpeg-$(CONFIG_SHARED)
++libffmpeg: $(LIBFFMPEG)
++
++install-libffmpeg: $(LIBFFMPEG)
++	$(Q)mkdir -p "$(SHLIBDIR)/chromium"
++	$(INSTALL) -m 755 $< "$(SHLIBDIR)/chromium/$<"
++	$(STRIP) "$(SHLIBDIR)/chromium/$<"
++
++uninstall-libffmpeg:
++	$(RM) "$(SHLIBDIR)/chromium/$(LIBFFMPEG)"
++
++.PHONY: libffmpeg libffmpeg-* install-libffmpeg
+-- 
+2.13.1
+