Having USE="ffmpeg" at all is the source of any confusion in case somebody is using libav. Either with an expand set (which seems wasted just for two options) or two regular flags, just force one or none. There is absolutely no sense in having USE="ffmpeg" on for a system using libav.
On Mon, Feb 2, 2015 at 8:12 AM, Ulrich Mueller <u...@gentoo.org> wrote: > >>>>> On Mon, 2 Feb 2015, Michał Górny wrote: > > > FFMPEG_IMPL feels like a natural extension of USE=ffmpeg. USE=ffmpeg > > tells to use ffmpeg or a replacement, FFMPEG_IMPL tells what will > > exactly get used. Much less confusion. > > > Thirdly, this opens space for having more than two different > > implementations in the future without having to reset the system. Maybe > > this isn't something worth considering but -- as I see it -- the first > > big fork starts a precedent, and both current versions suck :). > > > Fourthly, there's the case of implicity. Right now USE=-libav implies > > ffmpeg. Therefore, USE=-* implies ffmpeg as well -- which is kinda > > weird since it's supposedly the non-default. With this solution, USE=-* > > will result in explicit error asking user to select an implementation. > > > As for the downsides: > > > 1. there is a number of non-meaningful flag combinations. > > FFMPEG_IMPL='', FFMPEG_IMPL='ffmpeg libav'. They will have to be > > blocked via REQUIRED_USE='^^ ( ffmpeg_impl_ffmpeg ffmpeg_impl_libav )'. > > > 2. There is some more work to get ebuilds correct (REQUIRED_USE). > > However, this is a minor issue compared to the potential mistakes in > > interpretation of USE='ffmpeg' and USE='libav'. > > > > What are your thoughts? > > In a nutshell, you have a binary choice here, namely ffmpeg or libav > as implementation, and instead of one USE flag you want to introduce > two (ffmpeg_impl_ffmpeg and ffmpeg_impl_libav), but of the 4 possible > combinations only 2 are valid. So you need a REQUIRED_USE to forbid > some combinations. > > Please spare us of this. > > Ulrich >
