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avfilter/vf_libplacebo: introduce fit_mode option

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The semantics of these keywords are well-defined by the CSS 'object-fit'
property. This is arguably more user-friendly and less obtuse than the
existing `normalize_sar` and `pad_crop_ratio` options. Additionally, this
comes with two new (useful) behaviors, `none` and `scale_down`, neither of
which map elegantly to the existing options.

One additional benefit of this option is that, unlike `normalize_sar`, it
does *not* also imply `reset_sar`; meaning that users can now choose to
have an anamorphic base layer and still have the overlay images scaled to fit
on top of it according to the chosen strategy.

See-Also: https://drafts.csswg.org/css-images/#the-object-fit
This commit is contained in:
Niklas Haas
2025-09-08 18:28:19 +02:00
committed by Niklas Haas
parent 6ad839ff2e
commit 12d696cff4
2 changed files with 86 additions and 6 deletions
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36
doc/filters.texi
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@@ -16459,7 +16459,7 @@ e.g. anamorphic video sources, are forwarded to the output pixel aspect ratio.
@item normalize_sar
Like @option{reset_sar}, but instead of stretching the video content to fill
the new output aspect ratio, the content is instead padded or cropped as
necessary.
necessary. Mutually exclusive with @option{fit_mode}. Disabled by default.
@item pad_crop_ratio
Specifies a ratio (between @code{0.0} and @code{1.0}) between padding and
@@ -16469,6 +16469,40 @@ content with black borders, while a value of @code{1.0} always crops off parts
of the content. Intermediate values are possible, leading to a mix of the two
approaches.
@item fit_mode
Specify the content fit strategy according to a list of predefined modes.
Determines how the input image is to be placed inside the destination crop
rectangle (as defined by @code{pos_x/y} and @code{pos_w/h}). The names and
their implementations are taken from the CSS 'object-fit' property. Note that
this option is mutually exclusive with @option{normalize_sar}. Defaults to
@code{fill}. Valid values are:
@table @samp
@item fill
Stretch the input to the output rectangle, ignoring aspect ratio mismatches.
Note that unless @option{reset_sar} is also enabled, the output will still
have the correct pixel aspect ratio tagged.
@item contain
Scale the input to fit inside the output, preserving aspect ratio by padding.
Equivalent to @option{normalize_sar} with @option{pad_crop_ratio} set to
@code{0.0}.
@item cover
Scale the input to fill the output, preserving aspect ratio by cropping.
Equivalent to @option{normalize_sar} with @option{pad_crop_ratio} set to
@code{1.0}.
@item none, place
Don't scale the input. The input will be placed inside the output rectangle at
its natural size; which may result in additional padding or cropping.
@item scale_down
Scale the input down as much as needed to fit inside the output. Equivalent
to either @code{contain} or @code{none}, depending on whether the input is
larger than the output or not.
@end table
@item fillcolor
Set the color used to fill the output area not covered by the output image, for
example as a result of @option{normalize_sar}. For the general syntax of this