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avfilter/scale_eval: Reduce rounding error.

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When force_original_aspect_ratio and force_divisible_by are both
used, dimensions are now rounded to the nearest allowed multiple of
force_divisible_by rather than first rounding to the nearest integer and
then rounding in a static direction. This results in less distortion of
the aspect ratio.

Reviewed-by: Thierry Foucu <tfoucu@google.com>
Signed-off-by: Tristan Schmelcher <tschmelcher@google.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Tristan Schmelcher 2022-09-26 17:14:09 +00:00 committed by Michael Niedermayer
parent 543a46b4b2
commit 179830108d
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GPG Key ID: B18E8928B3948D64
2 changed files with 9 additions and 5 deletions
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11
libavfilter/scale_eval.c
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@ -148,14 +148,17 @@ int ff_scale_adjust_dimensions(AVFilterLink *inlink,
* dimensions so that it is not divisible by the set factors anymore
* unless force_divisible_by is defined as well */
if (force_original_aspect_ratio) {
int tmp_w = av_rescale(h, inlink->w, inlink->h);
int tmp_h = av_rescale(w, inlink->h, inlink->w);
// Including force_divisible_by here rounds to the nearest multiple of it.
int tmp_w = av_rescale(h, inlink->w, inlink->h * (int64_t)force_divisible_by)
* force_divisible_by;
int tmp_h = av_rescale(w, inlink->h, inlink->w * (int64_t)force_divisible_by)
* force_divisible_by;
if (force_original_aspect_ratio == 1) {
w = FFMIN(tmp_w, w);
h = FFMIN(tmp_h, h);
if (force_divisible_by > 1) {
// round down
// round down in case provided w or h is not divisible.
w = w / force_divisible_by * force_divisible_by;
h = h / force_divisible_by * force_divisible_by;
}
@ -163,7 +166,7 @@ int ff_scale_adjust_dimensions(AVFilterLink *inlink,
w = FFMAX(tmp_w, w);
h = FFMAX(tmp_h, h);
if (force_divisible_by > 1) {
// round up
// round up in case provided w or h is not divisible.
w = (w + force_divisible_by - 1) / force_divisible_by * force_divisible_by;
h = (h + force_divisible_by - 1) / force_divisible_by * force_divisible_by;
}

3
libavfilter/scale_eval.h
View File

@ -38,7 +38,8 @@ int ff_scale_eval_dimensions(void *ctx,
* Transform evaluated width and height obtained from ff_scale_eval_dimensions
* into actual target width and height for scaling. Adjustment can occur if one
* or both of the evaluated values are of the form '-n' or if
* force_original_aspect_ratio is set.
* force_original_aspect_ratio is set. force_divisible_by is used only when
* force_original_aspect_ratio is set and must be at least 1.
*
* Returns 0.
*/