[FFmpeg-devel] [PATCH] Ensure scaled video is divisible by n

[Paul B Mahol]

On 7/3/19, Lars Kiesow <lkiesow at uos.de> wrote:
> This patch adds a new option to the scale filter which ensures that the
> output resolution is divisible by the given integer similar to using -n
> in the `w` and `h` options. But this works even if the
> `force_original_aspect_ratio` is used.
>
> 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       | 5 +++++
>  libavfilter/vf_scale.c | 9 ++++++---
>  2 files changed, 11 insertions(+), 3 deletions(-)
>
> diff --git a/doc/filters.texi b/doc/filters.texi
> index 700a76f239..1694fdda28 100644
> --- a/doc/filters.texi
> +++ b/doc/filters.texi
> @@ -15215,6 +15215,11 @@ 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
> similar
> +to using -n in the @option{w} and @option{h} options. But this works even
> if
> +the @option{force_original_aspect_ratio} is used.
> +
>  @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 f741419e7e..1cc28f6a56 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;
>
> @@ -237,10 +238,11 @@ 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);
> +        int tmp_w = av_rescale(h, inlink->w, inlink->h) /
> scale->force_divisible_by * scale->force_divisible_by;
> +        int tmp_h = av_rescale(w, inlink->h, inlink->w) /
> scale->force_divisible_by * scale->force_divisible_by;
>
>          if (scale->force_original_aspect_ratio == 1) {
>               w = FFMIN(tmp_w, w);
> @@ -589,6 +591,7 @@ static const AVOption scale_options[] = {
>      { "out_v_chr_pos",   "output vertical chroma position in luma grid/256"
>  , OFFSET(out_v_chr_pos), AV_OPT_TYPE_INT, { .i64 = -513}, -513, 512, FLAGS
> },
>      { "out_h_chr_pos",   "output horizontal chroma position in luma
> grid/256", OFFSET(out_h_chr_pos), AV_OPT_TYPE_INT, { .i64 = -513}, -513,
> 512, FLAGS },
>      { "force_original_aspect_ratio", "decrease or increase w/h if necessary
> to keep the original AR", OFFSET(force_original_aspect_ratio),
> AV_OPT_TYPE_INT, { .i64 = 0}, 0, 2, FLAGS, "force_oar" },
> +    { "force_divisible_by", "endorce that the output resolution is
> devisible by a defined integer", OFFSET(force_divisible_by),

endorce and devisible are typos.

> AV_OPT_TYPE_INT, { .i64 = 1}, 0, 256, FLAGS, "force_oar" },
>      { "disable",  NULL, 0, AV_OPT_TYPE_CONST, {.i64 = 0 }, 0, 0, FLAGS,
> "force_oar" },
>      { "decrease", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = 1 }, 0, 0, FLAGS,
> "force_oar" },
>      { "increase", NULL, 0, AV_OPT_TYPE_CONST, {.i64 = 2 }, 0, 0, FLAGS,
> "force_oar" },
> --
> 2.21.0
>
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