Many filters accept user-provided data that is cumbersome to provide as
text strings - e.g. binary files or very long text. For that reason such
filters typically provide a option whose value is the path from which
the filter loads the actual data.
However, filters doing their own IO internally is a layering violation
that the callers may not expect, and is thus best avoided. With the
recently introduced graph segment parsing API, loading option values
from files can now be handled by the caller.
This commit makes use of the new API in ffmpeg CLI. Any option name in
the filtergraph syntax can now be prefixed with a slash '/'. This will
cause ffmpeg to interpret the value as the path to load the actual value
from.
This reverts commit dea673d0d5.
This change cannot work for several reasons, the most obvious ones are:
- the alpha is being part of the scoring of the color difference, even
though we can not interpret the alpha as part of the perception of the
color (we don't even know if it's premultiplied or postmultiplied)
- the colors are averaged with their alpha value which simply cannot
work
The command proposed in the original thread of the patch actually
produces a completely broken file:
ffmpeg -y -loglevel verbose -i fate-suite/apng/o_sample.png -filter_complex "split[split1][split2];[split1]palettegen=max_colors=254:use_alpha=1[pal1];[split2][pal1]paletteuse=use_alpha=1" -frames:v 1 out.png
We can see that many color pixels are off, but more importantly some
colors have a random alpha value: https://imgur.com/eFQ2UK7
I don't see any easy fix for this unfortunately, the approach appears to
be flawed by design.
As a result of a typo in the source code, this option was completely
non-functional. In order to fix it, without breaking the current default
behavior, explicitly change this default to 0.
This behavior is also consistent with how other scale filters behave by
default, so it's probably best to enshrine it anyways.
summary: This patch modifies the `curves` filter with new `interp` option
to let user pick the existing natural cubic spline interpolation
and the new PCHIP interapolation.
reason: The natural cubic spline does not impose monotonicity between
the keypoints. As such, the fitted curve may vary wildly against
user's intension. The PCHIP interpolation is not as smooth as
the natural spline but guarantees the monotonicity. Providing
both options enhances users experience (e.g., reduces the number
of keypoints to realize the desired curve). See the related bug
report for the example of an ill-interpolated curve.
alternate solution:
Both Photoshop and GIMP appear to use monotonic interpolation in
their curve tools, which were the models for this filter. As
such, an alternate solution is to drop the natural spline and
go without the `interp` option.
related bug report: https://trac.ffmpeg.org/ticket/9947 (filed by myself)
Signed-off-by: Takeshi (Kesh) Ikuma <tikuma@hotmail.com>
Apparently this option was intended (the context contains a
currently-unused frame_rate field), but was never added. This results in
the output timebase being unset after config_output(), so the input
audio timebase ends up being used for video output, which is clearly
wrong.
Add an option for setting output video framerate. Also set output frame
durations.
