[FFmpeg-devel] [PATCH v4 2/4] avfilter/vf_framerate: if metadata lavfi.scd.mafd exists, we'll use it first

Michael Niedermayer michael at niedermayer.cc
Fri Oct 11 21:13:02 EEST 2019


On Thu, Oct 10, 2019 at 10:11:10PM +0800, Limin Wang wrote:
> On Thu, Oct 10, 2019 at 01:52:56PM +0200, Michael Niedermayer wrote:
> > On Tue, Oct 08, 2019 at 11:28:37PM +0800, lance.lmwang at gmail.com wrote:
> > > From: Limin Wang <lance.lmwang at gmail.com>
> > > 
> > > Reviewed-by: Paul B Mahol <onemda at gmail.com>
> > > Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> > > ---
> > >  libavfilter/vf_framerate.c | 15 +++++++++++----
> > >  1 file changed, 11 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/libavfilter/vf_framerate.c b/libavfilter/vf_framerate.c
> > > index 6c8d01c..8d16998 100644
> > > --- a/libavfilter/vf_framerate.c
> > > +++ b/libavfilter/vf_framerate.c
> > > @@ -71,13 +71,20 @@ static double get_scene_score(AVFilterContext *ctx, AVFrame *crnt, AVFrame *next
> > >  
> > >      if (crnt->height == next->height &&
> > >          crnt->width  == next->width) {
> > > +        AVDictionaryEntry *e_mafd = NULL;
> > >          uint64_t sad;
> > > -        double mafd, diff;
> > > +        double mafd = HUGE_VAL, diff;
> > > +        char *tail = NULL;
> > >  
> > >          ff_dlog(ctx, "get_scene_score() process\n");
> > > -        s->sad(crnt->data[0], crnt->linesize[0], next->data[0], next->linesize[0], crnt->width, crnt->height, &sad);
> > > -        emms_c();
> > > -        mafd = (double)sad * 100.0 / (crnt->width * crnt->height) / (1 << s->bitdepth);
> > > +        e_mafd = av_dict_get(next->metadata, "lavfi.scd.mafd", NULL, AV_DICT_MATCH_CASE);
> > > +        if (e_mafd)
> > > +            mafd = strtod(e_mafd->value, &tail);
> > > +        if (*tail || mafd == HUGE_VAL) {
> > > +            s->sad(crnt->data[0], crnt->linesize[0], next->data[0], next->linesize[0], crnt->width, crnt->height, &sad);
> > > +            emms_c();
> > > +            mafd = (double)sad * 100.0 / (crnt->width * crnt->height) / (1 << s->bitdepth);
> > > +        }
> > 
> > while this is not introduced by the patch, i would suggest to seperate
> > emms_c() from functions using floating point, This combination does have
> > some potential for emms and the compilers optimizer hitting each other
> 
> Michael, I haven't clear about what to seperate the emms_c? any reference usage in 
> existing codebase? I can help to submit patch to fix it, there're at least five filters
> are using the same way.

emms clears the float/MMX state of the cpu
if the compiler uses the FPU at the same time and is unaware of that
clearing it could result in problems.
so i just always tried to keep emms away from floating point usage to minimize 
the chances of this.

also it was rather slow on some CPUs to mix mmx and float code 

thx
[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When you are offended at any man's fault, turn to yourself and study your
own failings. Then you will forget your anger. -- Epictetus
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