UPDATE: Added some basic migration instructions to the bottom.
UPDATE2: Removed mplayer incompatibility mention. Mplayer-1.1 works with system libav.
As the summary says the default media codec provider for new installs will be libav instead of ffmpeg.
This change is being done due to various reasons like matching default with Fedora and Debian, or due to fact that some projects which are high-profile (eg sh*tload of people use them) will be probably libav only. One example being gst-libav which is in return required by libreoffice-4 which is due release in about month. To go for least pain for the user we decided to move from default ffmpeg to default libav library.
This change won’t affect your current installs at all but we would like to ask you to try to migrate to the libav and test and report any issues. So if stuff happen in the future and we are forced to throw libav as only implementation for everyone you are not left in the dark screaming for your suddenly missing features.
What to do when some package does not build with libav but ffmpeg is fine
There are no such packages left around if I am searching correctly (might be my blindness so do not take my word for it).
So if you encounter any package not building with libav just open bugreport on bugzilla and assign it to media-video team and add lu_zero[at]gentoo.org to CC to be sure he really takes a sneaky look to fix it. If you want to fix the issue yourself it gets even better. You write the patch open the bug in our bugzie and someone will include it. Also the patch should be sent to upstream for inclusion, so we don’t have to keep the patches in tree for long time.
What should I do when I have some issues with libav and I require more features that are on ffmpeg but not on libav
Its easier than fixing bugs about failing packages. Just nag to lu_zero (mail hidden somewhere in this post ;-)) and read this.
So when is this stuff going to ruin my day?
The switch in the tree and news item informing all users of media-video/ffmpeg will be created at the end of the January or early February, unless something really bad happens while you guys test it now.
I feel lucky and I want to switch right away so I can ruin your day by reporting bugs
Great I am really happy you want to contribute. The libav switch is pretty easy to be done as there are only 2 things to keep in mind.
You have to sync your useflags between virtual/ffmpeg and the newly-to-be-switched media-video/libav. This is most probably best to do just edit your package.use stuff and replace the media-video/ffmpeg line with media-video/libav one.
Then one would go straight away for emerge libav but there is one more caveat. Libav has split libpostproc library while ffmpeg still is using the internal one. Code wise they are most probably equal but you have to take account for it so just call emerge with both libraries.
emerge -1v libav libpostproc
If this succeeds you have to revdep-rebuild the packages you have or use @preserved-rebuild from portage-2.2 to rebuild all the RDEPENDS of libav.
Good luck and happy bug hunting.