On date Sunday 2011-04-03 14:42:43 +0100, Måns Rullgård wrote:
> Stefano Sabatini <[email protected]> writes:
[...]
> > I suppose we can implement two policies:
> >
> > a. when a component is explicitely enabled, all the depending
> >    components are automatically enabled
> >
> > E.g.:
> > --enable-libx264 -> enable libx264-encoder, gpl
> > --enable-librtmp -> enable librtmp-muxer/demuxer
> >
> > b. when a component is explicitely enabled, check if the dependencies
> >    are enabled and fail otherwise; enable a component by default if
> >    all its dependencies are satisfied
> >
> > We currently have a mix of a. and b., and I find b. more usable and
> > safer, as the user becomes more aware of what she's enabling and what
> > not.
> >
> > For example the user wants to enable the libx264 encoder.
> > Currently we have:
> > $ configure --enable-encoder=libx264
> > => success, but libx264 and the libx264-encoder are not enabled
> >
> > With the b. approach:
> > $ configure --enable-encoder=libx264
> > => configure complains about missing gpl and libx264, and fails.
> >
> > $ configure --enable-libx264 --enable-gpl
> > => success, libx264-encoder is automatically enabled since its dependencies 
> > are satisfied
> >
> > If we want to use a pure a. approach we should automatically enable
> > gpl (while currently we have an ad-hoc license check) which doesn't
> > appear like a good idea from the legal POV, adopting a hybrid approach
> > (as currently implemented) is confusing.
> 

> There is nothing confusing at all.  Two simple rules:
>
> 1. Everything is enabled by default.
>
> 2. External libs must be explicitly enabled.

This is not changed by the patch, the raised issue is different, and
is that explicitely enabling an element should make configure issues
some warning.

Indeed the user doesn't know nothing about the internal dependencies,
but when she types --enable-thing=foobar she expects the element to
be enabled.

> Thus far, nobody has complained about this.  Until someone does, I'm not
> changing it.  Your meta-complaint does not count.

http://thread.gmane.org/gmane.comp.video.ffmpeg.user/30661/focus=30668
http://thread.gmane.org/gmane.comp.video.ffmpeg.user/30778/focus=30779

Both users complained about --enable-filter=drawtext, but the same
applies to other components, for example I find
--enable-encoder=libx264 not enabling the libx264 encoder and not
failing quite counter-intuitive.

(And not this is not a serious issue, consider this like a
"paperclip"/bikeshed issue).
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