[FFmpeg-devel] [PATCH v1] avfilter/vf_framerate: make the scene change detection calculation method consistent with f_select filter

[Limin Wang]

On Thu, Sep 12, 2019 at 07:55:30PM +0200, Marton Balint wrote:
> 
> 
> On Thu, 12 Sep 2019, lance.lmwang at gmail.com wrote:
> 
> >From: Limin Wang <lance.lmwang at gmail.com>
> >
> >Have been tested by fate-suite/svq3/Vertical400kbit.sorenson3.mov and the
> >testing results are consistent.
> >
> >If it is acceptable, I want to move get_scene_score() to the public function and
> >make the scene change detection calculation method of the relevant module consistent.
> >
> >Signed-off-by: Limin Wang <lance.lmwang at gmail.com>
> >---
> >doc/filters.texi           | 4 ++--
> >libavfilter/vf_framerate.c | 6 +++---
> >2 files changed, 5 insertions(+), 5 deletions(-)
> >
> >diff --git a/doc/filters.texi b/doc/filters.texi
> >index 9d500e44a9..1c2e86b635 100644
> >--- a/doc/filters.texi
> >+++ b/doc/filters.texi
> >@@ -10626,10 +10626,10 @@ the default is @code{240}.
> >
> >@item scene
> >Specify the level at which a scene change is detected as a value between
> >-0 and 100 to indicate a new scene; a low value reflects a low
> >+0 and 1.0 to indicate a new scene; a low value reflects a low
> 
> You cannot change the scale of a user facing parameter, that would break
> existing command lines.

Yes, I'm afraid of it when I'm change it. Then it's impossible to make
consistent.
> 
> >probability for the current frame to introduce a new scene, while a higher
> >value means the current frame is more likely to be one.
> >-The default is @code{8.2}.
> >+The default is @code{0.25}.
> 
> You should not change the default unless you have a very good
> reason, as it would change existing behaviour.
> 
> >
> >@item flags
> >Specify flags influencing the filter process.
> >diff --git a/libavfilter/vf_framerate.c b/libavfilter/vf_framerate.c
> >index 06e463e4d7..def3f19f55 100644
> >--- a/libavfilter/vf_framerate.c
> >+++ b/libavfilter/vf_framerate.c
> >@@ -51,7 +51,7 @@ static const AVOption framerate_options[] = {
> >
> >    {"interp_start",        "point to start linear interpolation",    OFFSET(interp_start),    AV_OPT_TYPE_INT,      {.i64=15},                 0,       255,     V|F },
> >    {"interp_end",          "point to end linear interpolation",      OFFSET(interp_end),      AV_OPT_TYPE_INT,      {.i64=240},                0,       255,     V|F },
> >-    {"scene",               "scene change level",                     OFFSET(scene_score),     AV_OPT_TYPE_DOUBLE,   {.dbl=8.2},                0,       INT_MAX, V|F },
> >+    {"scene",               "scene change level",                     OFFSET(scene_score),     AV_OPT_TYPE_DOUBLE,   {.dbl=0.25},               0,       1.0,     V|F },
> >
> >    {"flags",               "set flags",                              OFFSET(flags),           AV_OPT_TYPE_FLAGS,    {.i64=1},                  0,       INT_MAX, V|F, "flags" },
> >    {"scene_change_detect", "enable scene change detection",          0,                       AV_OPT_TYPE_CONST,    {.i64=FRAMERATE_FLAG_SCD}, INT_MIN, INT_MAX, V|F, "flags" },
> >@@ -77,9 +77,9 @@ static double get_scene_score(AVFilterContext *ctx, AVFrame *crnt, AVFrame *next
> >        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);
> >+        mafd = (double)sad / (crnt->width * crnt->height) / (1ULL << (s->bitdepth - 8));
> 
> No, dividing by bitdepth-8 is completely wrong. It is wrong in
> f_select, but we could not change it there as that would have
> changed the scale of a user facing option.
> 
I have changed vf_minterpolate filter, it divides (crnt->width * crnt->height * 3) which I think it's wrong, 
so I consider to make them using consistent method.  If we need to keep the user option unchanged, then 
it's impossible to do it. I'll submit the change for review.


> Regards,
> Marton
> 
> 
> >        diff = fabs(mafd - s->prev_mafd);
> >-        ret  = av_clipf(FFMIN(mafd, diff), 0, 100.0);
> >+        ret  = av_clipf(FFMIN(mafd, diff) / 100., 0, 1);
> >        s->prev_mafd = mafd;
> >    }
> >    ff_dlog(ctx, "get_scene_score() result is:%f\n", ret);
> >-- 
> >2.21.0
> >
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