There's no reason to use a completely separate graph just to process the
alpha plane in isolation - zimg supports native alpha handling as part of the
main image.
Fixes several issues with this filter when adding or removing alpha planes,
and also adds support for scaling premultiplied alpha (which reduces artefacts
near the image borders).
Fortunately, we only care if this flag is set - otherwise, this filter is
alpha mode agnostic (since it is purely scaling, etc).
That said, there is an argument to be made that we should prefer premul
alpha when scaling, because scaling in straight alpha will leak garbage
pixels; but I think that would be a too backwards-incompatible change to
be worth thinking about at this time.
The overwhelming majority of references to ff_draw_init2() just set the
colorspace properties from a filter link. This wrapper allows us to update
all such referencen automatically.
Conceptually, these are pretty simple to handle, since they are basically
equivalent to the case of alpha being absent, since the only thing the
destination alpha plane is used for is unpremultiplyng straight alpha.
For planar formats, the total number of cases doesn't change in principle,
since before this patch we have:
- alpha present, overlay straight
- alpha present, overlay premultiplied
- alpha absent, overlay straight
- alpha absent, overlay premultiplied
And now we have:
- main straight, overlay straight
- main straight, overlay premultiplied
- main premultiplied, overlay straight
- main premultiplied, overlay premultiplied
That said, we do gain some cases now that we used to (incorrectly) ignore,
like premultiplied yuva420p10.
Notably, we can skip defining separate functions for the case of main alpha
being absent, since that can be a single cheap branch inside the function
itself, on whether or not to also process the alpha plane. Otherwise, as long
as we treat "alpha absent" as "main premultiplied", the per-plane logic will
skip touching the nonexistent alpha plane.
The only format that actually needs extra cases is packed rgb, but that's only
two additional cases in total.
Also arguably simplifies the assignment logic massively.
Chooses the desired output alpha mode. Note that this depends on
an upstream version of libplacebo new enough to respect the corresponding
AVFrame field in pl_map_avframe_ex.
While vf_scale cannot directly convert between premultiplied and straight
alpha, the effective tagging can still change as a result of a change in
the pixel format (i.e. adding or removing an alpha channel).
JPEG XL supports both premultiplied and straight alpha, and the basic info
struct contains signalling for this. Forward the correct tagging on decode
and encode.
OpenEXR always uses premultiplied alpha, as per the spec.
cf. https://openexr.com/en/latest/TechnicalIntroduction.html
> By convention, all color channels are premultiplied by alpha, so that
> `foreground + (1-alpha) x background` performs a correct “over” operation.
> (See Premultiplied vs. Un-Premultiplied Color Channels)
>
> In the visual effects industry premultiplied color channels are the norm,
> and application software packages typically use internal image
> representations that are also premultiplied.
PNG always uses straight alpha.
cf. https://www.w3.org/TR/PNG-Rationale.html
> Although each form of alpha storage has its advantages, we did not want to
> require all PNG viewers to handle both forms. We standardized on non-
> premultiplied alpha as being the lossless and more general case.
Following in the footsteps of the previous commit, this commit adds the
new fields to AVCodecContext so we can start properly setting it on codecs,
as well as limiting the list of supported options to detect a format mismatch
during encode.
This commit also sets up the necessary infrastructure to start using the
newly added field in all codecs.
We need a filter that can premultiply and unpremultiply the alpha channel
dynamically, on demand, in response to the negotiated alpha mode, analogous
to how vf_scale operates. Introduce a new filter "vf_premultiply_dynamic"
that accomplishes this.
Set the output link according to the chosen direction, and the input link
to its opposite (unless the input is not in-place, in which case there is no
alpha channel).
Also update the alpha mode on the output frame, since it may differ.
Instead of hard-coding the assumption that all video properties are handled
by vf_scale, generalize the struct slightly to allow different conversion
filters for each property being merged. The avfiltergraph code creates a list
of conversion filters needed and inserts all of them at once.
Because a conversion filter might itself e.g. not support all formats,
it's possible that we need to go through the whole process of negotiating
formats multiple times, and keep adding conversion filters until all of them
are settled. Do this by simply jumping back to the beginning of the loop
to ensure that the `convertor_count` field remains contiguous.
FFmpeg currently handles alpha in a quasi-arbitrary way. Some filters/codecs
assume alpha is premultiplied, others assume it is independent. If there is
to be any hope for order in this chaos, we need to start by defining an enum
for the possible range of values.
Use ff_adts_header_parse_buf() wrapper to simplify as GetBitContext is
no longer needed (it was introduced for USAC).
Partially reverts 64bb91fd3b.
Signed-off-by: Nicolas Gaullier <nicolas.gaullier@cji.paris>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
d119ae2fd8 removed the loop-breaking condition
received_sigterm.
Thus, signals no longer gracefully shutdown ffmpeg.
Fixes: #10834
Signed-off-by: Patrick Wang <mail6543210@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
If we're invoked with range == UINT_MAX, we end up doing
"rnd() % (UINT_MAX + 1)", which is equal to "rnd() % 0". On
arm (on all platforms) and on MSVC i386, this ends up crashing
at runtime.
This fixes the crash.
Zhao Zhili