[FFmpeg-devel] [PATCH] libavfilter/vf_scale: Ensure scaled video is divisible by n

[Michael Niedermayer]

On Mon, Jul 08, 2019 at 05:43:40PM +0200, Lars Kiesow wrote:
> This patch adds a new option to the scale filter which ensures that the
> output resolution is divisible by the given integer when used together
> with `force_original_aspect_ratio`. This works similar to using `-n` in
> the `w` and `h` options.
> 
> This option respects the value set for `force_original_aspect_ratio`,
> increasing or decreasing the resolution accordingly.
> 
> The use case for this is to set a fixed target resolution using `w` and
> `h`, to use the `force_original_aspect_ratio` option to make sure that
> the video always fits in the defined bounding box regardless of aspect
> ratio, but to also make sure that the calculated output resolution is
> divisible by n so in can be encoded with certain encoders/options if
> that is required.
> 
> Signed-off-by: Lars Kiesow <lkiesow at uos.de>
> ---
>  doc/filters.texi       | 12 ++++++++++++
>  libavfilter/vf_scale.c | 13 ++++++++++++-
>  2 files changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/doc/filters.texi b/doc/filters.texi
> index ee6a93ffbf..2de71d9820 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -15231,6 +15231,18 @@ Please note that this is a different thing than specifying -1 for @option{w}
>  or @option{h}, you still need to specify the output resolution for this option
>  to work.
>  
> + at item force_divisible_by Ensures that the output resolution is divisible by the
> +given integer when used together with @option{force_original_aspect_ratio}. This
> +works similar to using -n in the @option{w} and @option{h} options.
> +
> +This option respects the value set for @option{force_original_aspect_ratio},
> +increasing or decreasing the resolution accordingly. This may slightly modify
> +the video's aspect ration.
> +
> +This can be handy, for example, if you want to have a video fit within a defined
> +resolution using the @option{force_original_aspect_ratio} option but have
> +encoder restrictions when it comes to width or height.
> +
>  @end table
>  
>  The values of the @option{w} and @option{h} options are expressions
> diff --git a/libavfilter/vf_scale.c b/libavfilter/vf_scale.c
> index 7aebf56ad8..3ce6cdd1d5 100644
> --- a/libavfilter/vf_scale.c
> +++ b/libavfilter/vf_scale.c
> @@ -86,6 +86,7 @@ typedef struct ScaleContext {
>      int in_v_chr_pos;
>  
>      int force_original_aspect_ratio;
> +    int force_divisible_by;
>  
>      int nb_slices;
>  
> @@ -237,7 +238,8 @@ static int config_props(AVFilterLink *outlink)
>          goto fail;
>  
>      /* Note that force_original_aspect_ratio may overwrite the previous set
> -     * dimensions so that it is not divisible by the set factors anymore. */
> +     * dimensions so that it is not divisible by the set factors anymore
> +     * unless force_divisible_by is defined as well */
>      if (scale->force_original_aspect_ratio) {
>          int tmp_w = av_rescale(h, inlink->w, inlink->h);
>          int tmp_h = av_rescale(w, inlink->h, inlink->w);
> @@ -245,9 +247,17 @@ static int config_props(AVFilterLink *outlink)
>          if (scale->force_original_aspect_ratio == 1) {
>               w = FFMIN(tmp_w, w);
>               h = FFMIN(tmp_h, h);
> +             if (scale->force_divisible_by > 1) {
> +                 w = w / scale->force_divisible_by * scale->force_divisible_by;
> +                 h = h / scale->force_divisible_by * scale->force_divisible_by;
> +             }
>          } else {
>               w = FFMAX(tmp_w, w);
>               h = FFMAX(tmp_h, h);

> +             if (scale->force_divisible_by > 1) {
> +                 w = ceil(w / (float)scale->force_divisible_by) * scale->force_divisible_by;
> +                 h = ceil(h / (float)scale->force_divisible_by) * scale->force_divisible_by;

you dont need float here and its better not to use float when not needed
so theres a chance less for platform bitexactness issues

Thanks

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Modern terrorism, a quick summary: Need oil, start war with country that
has oil, kill hundread thousand in war. Let country fall into chaos,
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people, be surprised about them taking revenge and drop even more bombs
and strip your own citizens of their rights and freedoms. to be continued
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