[FFmpeg-devel] [PATCH 4/4] Make the crop filter accept parametric expressions.
Michael Niedermayer
michaelni
Fri Sep 10 11:35:54 CEST 2010
On Fri, Sep 10, 2010 at 09:50:14AM +0200, Stefano Sabatini wrote:
> On date Thursday 2010-09-09 15:29:20 +0200, Michael Niedermayer encoded:
> > On Thu, Sep 09, 2010 at 12:06:16PM +0200, Stefano Sabatini wrote:
> > > On date Thursday 2010-09-09 01:11:42 +0200, Stefano Sabatini encoded:
> > > > On date Wednesday 2010-09-08 15:56:27 +0200, Michael Niedermayer encoded:
> > > > > On Thu, Jul 22, 2010 at 07:52:35PM +0200, Stefano Sabatini wrote:
> > > > [...]
> > > > > > diff --git a/libavfilter/vf_crop.c b/libavfilter/vf_crop.c
> > > > > > index 6a7ae70..df9b5a2 100644
> > > > > > --- a/libavfilter/vf_crop.c
> > > > > > +++ b/libavfilter/vf_crop.c
> > > > > > @@ -24,7 +24,31 @@
> > > > > > */
> > > > > >
> > > > > > #include "avfilter.h"
> > > > > > +#include "libavutil/eval.h"
> > > > > > #include "libavutil/pixdesc.h"
> > > > > > +#include "libavutil/avstring.h"
> > > > > > +
> > > > > > +static const char *var_names[] = {
> > > > > > + "E",
> > > > > > + "PHI",
> > > > > > + "PI",
> > > > > > + "x",
> > > > > > + "y",
> > > > > > + "w", ///< width of the input video
> > > > > > + "h", ///< height of the input video
> > > > >
> > > > > t for timestamp in seconds
> > > > > f for frame number
> > > >
> > > > This will be only possible for x and y, as w and h cannot (yet) be
> > > > dynamically changed.
> > >
> > > Another idea would be to implement a separate cropeval filter in the
> >
> > no
> >
> >
> > > same file partly sharing the crop code, and perform x/y evaluation and
> > > validity checks in start_frame() (this to avoid to slow down the crop
> > > filter, which currently does just one evaluation during the
> > > configuration stage).
> >
> > mplayer has a filter that does a eval per pixel so i dont think one per
> > frame will kill you
>
> Done like this.
>
> >
> > >
> > > In the same way we could also add a cropfile filter which takes the
> > > crop values to be applied from a file, that would be useful for a
> >
> > allow eval to read from a file, more generic more flexible and more usefull
>
> I need to think more about how to implement this.
>
> Patch updated.
> --
> FFmpeg = Faithless and Free Mysterious Proud Eccentric Generator
> doc/filters.texi | 63 ++++++++++++++++++++++++------
> libavfilter/vf_crop.c | 105 +++++++++++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 151 insertions(+), 17 deletions(-)
> abc8b6a67d12f3a518009ee944046c112ad57d89 0001-Make-the-crop-filter-accept-parametric-expressions.patch
> From 81d82795d0d27de72982bc6f49961d7221906f29 Mon Sep 17 00:00:00 2001
> From: Stefano Sabatini <stefano.sabatini-lala at poste.it>
> Date: Thu, 9 Sep 2010 01:05:04 +0200
> Subject: [PATCH] Make the crop filter accept parametric expressions.
>
> ---
> doc/filters.texi | 63 ++++++++++++++++++++++++------
> libavfilter/vf_crop.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++--
> 2 files changed, 151 insertions(+), 17 deletions(-)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 60ecf56..e0627dd 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -28,32 +28,71 @@ Below is a description of the currently available video filters.
>
> Crop the input video to @var{x}:@var{y}:@var{width}:@var{height}.
>
> - at example
> -./ffmpeg -i in.avi -vf "crop=0:0:0:240" out.avi
> - at end example
> +The parameters are expressions containing the following constants:
>
> - at var{x} and @var{y} specify the position of the top-left corner of the
> -output (non-cropped) area.
> + at table @option
> + at item E, PI, PHI
> +the corresponding mathematical approximated values for e
> +(euler number), pi (greek PI), PHI (golden ratio)
>
> -The default value of @var{x} and @var{y} is 0.
> + at item TB
> +the input timebase used for the timestamps
> +
> + at item w, h
> +the input width and heigth.
>
> -The @var{width} and @var{height} parameters specify the width and height
> -of the output (non-cropped) area.
> + at item x, y
> +the computed values for @var{x} and @var{y}.
> +
> + at item n
> +the number of input frame, starting from 0
> +
> + at item pos
> +the position in the file of the input frame, -1 if unknown
should be NAN if unknown
>
> -A value of 0 is interpreted as the maximum possible size contained in
> -the area delimited by the top-left corner at position x:y.
> + at item pts
> +presentation time stamp of the input frame, expressed in TB units
time stamp should be in seconds, its unlikely that the user cares
about the timebase or even knows what it is in the crop filter
[...]
> +#define PARSE_AND_EVAL(var, var_expr) \
> + if ((ret = av_parse_and_eval_expr(&res, (expr = var_expr), var_names, crop->var_values, \
> + NULL, NULL, NULL, NULL, NULL, 0, ctx)) < 0) \
> + goto fail_expr; \
> + var = res;
> +
> + PARSE_AND_EVAL(crop->w, crop->w_expr);
> + PARSE_AND_EVAL(crop->h, crop->h_expr);
i dont think you need this macro here, and imho its just obfuscating what you
do
>
> av_log(link->dst, AV_LOG_INFO, "x:%d y:%d w:%d h:%d\n",
> crop->x, crop->y, crop->w, crop->h);
> @@ -110,6 +175,11 @@ static int config_input(AVFilterLink *link)
> }
>
> return 0;
> +
> +fail_expr:
> + av_log(NULL, AV_LOG_ERROR,
> + "Error when evaluating the expression '%s'\n", expr);
> + return ret;
> }
>
> static int config_output(AVFilterLink *link)
> @@ -131,6 +201,22 @@ static void start_frame(AVFilterLink *link, AVFilterBufferRef *picref)
> picref->video->w = crop->w;
> picref->video->h = crop->h;
>
> + crop->var_values[PTS] = picref->pts;
> + crop->var_values[POS] = picref->pos;
> + crop->x = crop->var_values[X] = av_eval_expr(crop->x_pexpr, crop->var_values, NULL);
> + crop->y = crop->var_values[Y] = av_eval_expr(crop->y_pexpr, crop->var_values, NULL);
you must evaluate X after Y again so Y is available to X
also i think the values should be cliped into sane integer range and maybe a
NAN check is needed to
[...]
--
Michael GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB
No great genius has ever existed without some touch of madness. -- Aristotle
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