[FFmpeg-devel] [RFC] Specifying KEYINT (-g) has no effect in libx264

[Etienne Buira]

On Mon, May 23, 2011 at 01:32:15AM -0700, Baptiste Coudurier wrote:
> On 5/22/11 8:33 PM, Michael Niedermayer wrote:
> > On Sun, May 22, 2011 at 10:40:07PM +0200, Stefano Sabatini wrote:
> >> Hi,
> >>
> >> see issue #157.
> >>
> >> The problem was possibly introduced in:
> >>
> >> commit 0140d3f0921e5cbb6ea8706acb0307f7ff57a133
> >> Author: Baptiste Coudurier <baptiste.coudurier at gmail.com>
> >> Date:   Sat Apr 16 16:50:50 2011 -0700
> >>
> >>     In libx264 wrapper, add -preset and -tune options
> >>
> >> and depends on the fact that x264_param_default_preset() which is
> >> called in x264_init(), calls x264_param_default() which defaults the
> >> already set options.
> >>
> >> Indeed order of options matters, with the current mechanism options
> >> are set in the relevant contexts, and globally processed in the object
> >> initialization, so the order specified on the commandline is basically
> >> ignored.
> >>
> >> In the case of libx264 we may process profile/preset *before* the
> >> other options set in the context, so that specific settings will
> >> override profile/preset information.
> 
> No, order doesn't matter, as long as a preset is specified, it will
> override other options.
> 
> >> This has the problem that most of the times user-set options are
> >> changed to medium profile or libx264 will complain&exit, see:
> >>
> >> thus making fine-tuned user options pointless (since they are changed
> >> to medium preset and/or will be rejected by libx264).
> 
> No, you can still specify fine-tuned options without a preset.
> 
> > I see 3 obvious solutions
> > 
> > A. is mplayers to just use -x264opts which ive added
> > 
> > B. keep track of which options have been set by the user and which are
> >    default.
> 
> 'B' is how it should be done. It's trivial, just remap "g" in the
> libx264.c the way weightp was mapped.

That covers the cli case, but libavcodec users might have surprises.

What about:
x264_param_default()
apply_avcodeccontext_values(blindly)
if (preset or tune specified) {
    x264_param_default_preset()
    apply_avcodeccontext_values(if_different_than_default)
}

Also, I think we can drop check_default_settings (which looks like to
contain a "100" vs "1000" typo when checking bitrate btw).