This patch will add MPEG4 encoder using Android Mediacodec
Signed-off-by: Samuel Mira <samuel.mira@qt.io<mailto:samuel.mira@qt.io>>
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
The only encoders avaliable using mediacodec were h264 and hevc. This
patch adds the vp9 encoder.
Signed-off-by: Samuel Mira <samuel.mira@qt.io<mailto:samuel.mira@qt.io>>
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
This patch add another ARIB caption decoder using libaribcaption
external library.
Unlike libaribb24, it supports 3 types of subtitle outputs:
* text: plain text
* ass: ASS formatted text
* bitmap: bitmap image
Default subtitle type is ass as same as libaribb24.
Advantages compared with libaribb24 on ASS subtitle are:
* Subtitle positioning.
* Multi-rect subtitle: some captions are displayed at different
position at a time.
* More stability and reproducibility.
To compile with this feature:
* libaribcaption external library has to be pre-installed.
https://github.com/xqq/libaribcaption
* configure with `--enable-libaribcaption` option.
`--enable-libaribb24` and `--enable-libaribcaption` options are
not exclusive. If both enabled, libaribcaption precedes as
order listed in `libavcodec/allcodecs.c`.
Signed-off-by: rcombs <rcombs@rcombs.me>
This allows users to specify an argument such as './configure
--enable-lto=thin' to use ThinLTO with Clang. The old functionality with
'./configure --enable-lto' is preserved.
Signed-off-by: J. Dekker <jdek@itanimul.li>
HLS segments may be MPEG-TS or fragmented MP4, so those (de)muxers are
required for reading/writing HLS media segments.
Fixes functionality with --disable-everything --enable-demuxer=hls
--enable-muxer=hls
This commit does for AVOutputFormat what commit
20f9727018 did for AVCodec:
It adds a new type FFOutputFormat, moves all the internals
of AVOutputFormat to it and adds a now reduced AVOutputFormat
as first member.
This does not affect/improve extensibility of both public
or private fields for muxers (it is still a mess due to lavd).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Signed-off-by: Anton Khirnov <anton@khirnov.net>
Like what we did for scale_qsv filter, we use QSVVPPContext as a base
context to manage MFX session for deinterlace_qsv filter.
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
Use QSVVPPContext as a base context of QSVScaleContext, hence we may
re-use functions defined for QSVVPPContext to manage MFX session for
scale_qsv filter.
In addition, system memory has been taken into account in
QSVVVPPContext, we may add support for non-QSV pixel formats in the
future.
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
It is a URL rewriter for IPFS gateways, not an actual implementation of
IPFS, and naming it as such was both incorrect and misleading.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Currently, several components select atsc_a53, despite
not using anything from it themselves. They only select
it because parsing SEI messages adds an indirect dependency.
But using direct dependencies is more natural, so add
dedicated subsystems for them.
It already allows to remove a superfluous dependency of
the HEVC QSV encoder on hevc_sei and atsc_a53.
Adding new subsystems only becomes effective after a reconfiguration.
In order to force this, some needed headers (which are only included
implicitly before this commit) were included explicitly in
libavformat/allformats.c.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Add qsv_transcode example which shows how to use qsv to do hardware
accelerated transcoding, also show how to dynamically set encoding
parameters.
examples:
Normal usage:
qsv_transcode input.mp4 h264_qsv output.mp4 "g 60"
Dynamic setting usage:
qsv_transcode input.mp4 hevc_qsv output.mp4 "g 60 asyne_depth 1"
100 "g 120"
This command initializes codec with gop_size 60 and change it to
120 after 100 frames
Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
x265_sei is available since X265_BUILD 88. Bump required version
to 89 to fix the regression from commit 1f58503013, and remove a
conditional compilation.
Signed-off-by: Zhao Zhili <zhilizhao@tencent.com>
added a new option 'a53cc' (on by default, as in libx264) for rendering
AV_FRAME_DATA_A53_CC as hevc sei payloads.
the code is a blend of the libx265.c code for writing
AV_FRAME_DATA_SEI_UNREGISTERED with the libx264.c code for writing atsc
a/53 payloads.
It is the only encoder supporting quarter samples.
This also allows to remove the qpeldsp dependency from
mpegvideo_enc.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The only thing from the H.263 decoder that is reachable
by the VC-1 decoder is ff_h263_decode_init(); but it does
not even use all of it; e.g. h263dsp is unused and so are
the VLCs initialized in ff_h263_decode_init() (they amount
to about 77KB which are now no longer touched).
Notice that one could also call ff_idctdsp_init()
directly instead of ff_mpv_idct_init(); one could even
do so in ff_vc1_init_common().
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The only msmpeg4 code that is ever executed by the VC-1 based
decoders is ff_msmpeg4_decode_init() and what is directly
reachable from it. This is:
a) A call to av_image_check_size(), then ff_h263_decode_init(),
b) followed by setting [yc]_dc_scale_table and initializing
scantable/permutations.
c) Afterwards, some static tables are initialized.
d) Finally, slice_height is set.
The replacement for ff_msmpeg4_decode_init() performs a)
just like now; it also sets [yc]_dc_scale_table,
but it only initializes inter_scantable and intra_scantable
and not permutated_intra_[hv]_scantable: The latter are only
used inside decode_mb callbacks which are only called
in ff_h263_decode_frame() which is unused for VC-1.*
The static tables initialized in c) are not used at all by
VC-1 (the ones that are used have been factored out in
previous commits); this avoids touching 327KiB of .bss.
slice_height is also not used by the VC-1 decoder (setting
it in ff_msmpeg4_decode_init() is probably redundant after
b34397b4cd).
*: It follows from this that the VC-1 decoder is not really
based upon the H.263 decoder either; changing this will
be done in a future commit.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The encoder is fixed point, and uses an MDCT only for analysis. Due
to the slightly different rounding, the encoder makes a different
decision, so the tests have to be adjusted as well.
This patch replaces the transform used in AAC with lavu/tx and removes
the limitation on only being able to decode 960-sample files
with the float decoder.
This commit also removes a whole bunch of unnecessary and slow
lifting steps the decoder did to compensate for the poor accuracy
of the old integer transformation code.
Overall float decoder speedup on Zen 3 for 64kbps: 32%
The encoder seems to be trading blows with hevc_nvenc.
In terms of quality at low bitrate cbr settings, it seems to
outperform it even. It produces fewer artifacts and the ones it
does produce are less jarring to my perception.
At higher bitrates I had a hard time finding differences between
the two encoders in terms of subjective visual quality.
Using the 'slow' preset, av1_nvenc outperformed hevc_nvenc in terms
of encoding speed by 75% to 100% while performing above tests.
Needless to say, it always massively outperformed h264_nvenc in terms
of quality for a given bitrate, while also being slightly faster.
Support for building with older versions of MSVC (with the
c99wrap/c99conv frontend) was removed in
ce943dd6ac.
Signed-off-by: Martin Storsjö <martin@martin.st>
This effectively reverts 9b78abae19.
The underlying issue has been fixed properly in commit
cff480e49d.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The eatqi decoder uses a custom IDCT and actually does not
use the IDCTDSP API at all. Somehow it was nevertheless
used to simply apply the identity permutation on ff_zigzag_direct.
This commit stops doing so.
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The eatgq decoder uses a custom IDCT and actually does not
use the IDCTDSP API at all. Somehow it was nevertheless
used to simply apply the identity permutation on ff_zigzag_direct.
This commit stops doing so. It also renames perm to scantable,
because it is only the scantable as given by the spec without
any further permutation performed by us.
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The eamad decoder uses a custom IDCT and actually does not
use the IDCTDSP API at all. Somehow it was nevertheless
used to simply apply the identity permutation on ff_zigzag_direct.
This commit stops doing so.
Reviewed-by: Peter Ross <pross@xvid.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
librav1e provides a function to create extradata, so use it instead of
extracting the sequence header OBU from packets.
Signed-off-by: James Almer <jamrial@gmail.com>
The binkaudio decoders don't need mdct or sinewin at all;
and binkaudio_dct doesn't need rdft directly (but nevertheless
uses it indirectly via dct).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
As long as ff_mpeg12_common_init() existed in mpeg12.c,
it added a dependency of mpeg12.o on mpegvideodata.o
(which provides ff_mpeg2_dc_scale_table, which is used
in ff_mpeg12_common_init()). mpegvideodata.o is normally
provided by the mpegvideo subsystem and therefore several
codecs and the MPEG-1/2 parser added a configure dependency
on said subsystem (additionally, the eatqi decoder just
added a Makefile dependency on mpegvideodata.o).
Given that ff_mpeg12_common_init() is no more, these dependencies
can be removed.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
Starting with an h264 implementation. Can be extended to support other codecs.
A few caveats:
- OpenGOP streams are currently not supported. The firt packet must be an IDR
frame.
- In some streams, a few frames at the end may not get a reordered PTS when
they reference frames past EOS. The code added to derive timestamps from
previous frames needs to extended.
Addresses ticket #502.
Signed-off-by: James Almer <jamrial@gmail.com>
RISC-V defines the CLZ instruction as part of the ratified Zbb subset
of the (not yet ratified) bit mapulation extension (B). We can detect
it from the __riscv_zbb predefined constant. At least GCC 12 already
supports this correctly.
Note that the macro will be non-zero if supported, zero if enabled
in the compiler flags (e.g. -march=rv64gzbb) but not known to the
compiler, and undefined otherwise.
_Float16 support was available on arm/aarch64 for a while, and with gcc
12 was enabled on x86 as long as SSE2 is supported.
If the target arch supports f16c, gcc emits fairly efficient assembly,
taking advantage of it. This is the case on x86-64-v3 or higher.
Same goes on arm, which has native float16 support.
On x86, without f16c, it emulates it in software using sse2 instructions.
This has shown to perform rather poorly:
_Float16 full SSE2 emulation:
frame=50074 fps=848 q=-0.0 size=N/A time=00:33:22.96 bitrate=N/A speed=33.9x
_Float16 f16c accelerated (Zen2, --cpu=znver2):
frame=50636 fps=1965 q=-0.0 Lsize=N/A time=00:33:45.40 bitrate=N/A speed=78.6x
classic half2float full software implementation:
frame=49926 fps=1605 q=-0.0 Lsize=N/A time=00:33:17.00 bitrate=N/A speed=64.2x
Hence an additional check was introduced, that only enables use of
_Float16 on x86 if f16c is being utilized.
On aarch64, a similar uplift in performance is seen:
RPi4 half2float full software implementation:
frame= 6088 fps=126 q=-0.0 Lsize=N/A time=00:04:03.48 bitrate=N/A speed=5.06x
RPi4 _Float16:
frame= 6103 fps=158 q=-0.0 Lsize=N/A time=00:04:04.08 bitrate=N/A speed=6.32x
Since arm/aarch64 always natively support 16 bit floats, it can always
be considered fast there.
I'm not aware of any additional platforms that currently support
_Float16. And if there are, they should be considered non-fast until
proven fast.
This allows user to build FFmpeg against Intel oneVPL. oneVPL 2.6
is the required minimum version when building Intel oneVPL code.
It will fail to run configure script if both libmfx and libvpl are
enabled.
It is recommended to use oneVPL for new work, even for currently available
hardwares [1]
Note the preferred child device type is d3d11va for libvpl on Windows.
The commands below will use d3d11va if d3d11va is available on Windows.
$ ffmpeg -hwaccel qsv -c:v h264_qsv ...
$ ffmpeg -qsv_device 0 -hwaccel qsv -c:v h264_qsv ...
$ ffmpeg -init_hw_device qsv=qsv:hw_any -hwaccel qsv -c:v h264_qsv ...
$ ffmpeg -init_hw_device qsv=qsv:hw_any,child_device=0 -hwaccel qsv -c:v h264_qsv ...
User may use child_device_type option to specify child device type to
dxva2 or derive a qsv device from a dxva2 device
$ ffmpeg -init_hw_device qsv=qsv:hw_any,child_device=0,child_device_type=dxva2 -hwaccel qsv -c:v h264_qsv ...
$ ffmpeg -init_hw_device dxva2=d3d9:0 -init_hw_device qsv=qsv@d3d9 -hwaccel qsv -c:v h264_qsv ...
[1] https://www.intel.com/content/www/us/en/develop/documentation/upgrading-from-msdk-to-onevpl/top.html
The following Cflags has been added to libmfx.pc, so mfx/ prefix is no
longer needed when including mfx headers in FFmpeg.
Cflags: -I${includedir} -I${includedir}/mfx
Some old versions of libmfx have the following Cflags in libmfx.pc
Cflags: -I${includedir}
We may add -I${includedir}/mfx to CFLAGS when running 'configure
--enable-libmfx' for old versions of libmfx, if so, mfx headers without
mfx/ prefix can be included too.
If libmfx comes without pkg-config support, we may do a small change to
the settings of the environment(e.g. set -I/opt/intel/mediasdk/include/mfx
instead of -I/opt/intel/mediasdk/include to CFLAGS), then the build can
find the mfx headers without mfx/ prefix
After applying this change, we won't need to change #include for mfx
headers when mfx headers are installed under a new directory.
This is in preparation for oneVPL support (mfx headers in oneVPL are
installed under vpl directory)
The data structures for VP9 in mfxvp9.h is wrapped by
MFX_VERSION_NEXT, which means those data structures have never been used
in a public release. Actually MFX_CODEC_VP9 and other VP9 stuffs are
added in mfxstructures.h. In addition, mfxdefs.h is included in
mfxvp9.h, so we may use the check in this patch for MFX_CODEC_VP9
This is in preparation for oneVPL support because mfxvp9.h is removed
from oneVPL [1]
[1]: https://github.com/oneapi-src/oneVPL
Intel's oneVPL is a successor to MediaSDK, but removed some obsolete
features of MediaSDK[1], some early versions of oneVPL still use libmfx
as library name[2]. However some of obsolete features, including OPAQUE
memory, multi-frame encode, user plugins and LA_EXT rate control mode
etc, have been enabled in QSV, so user can not use --enable-libmfx to
enable QSV if using an early version of oneVPL SDK. In order to ensure
user builds FFmpeg against a right version of libmfx, this patch added a
check for version < 2.0 and warning message about the used obsolete
features.
[1] https://spec.oneapi.io/versions/latest/elements/oneVPL/source/VPL_intel_media_sdk.html
[2] https://github.com/oneapi-src/oneVPL
The msmpeg4 decoders/encoders share a common set of prerequisites,
ergo it makes sense to use common subsystems for them. This also
allows to remove the CONFIG_MSMPEG4_DECODER/ENCODER ad-hoc defines
(which violated the CONFIG_ namespace).
Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
IntraX8 uses WMV2DSP directly, so it should have a direct dependency
on it. Also remove the indirect Makefile dependency of the VC-1 decoder
on wmv2dsp.o. Notice that since the addition of the MIPS WMV2DSP
implementation building only the VC-1 decoder would fail, because
no Makefile dependency VC1->wmv2dsp_init_mips.o has been added.
This is of course fixed by this commit.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
The DXGI_OUTDUPL_FRAME_INFO type isn't available in Windows API
subsets other than "desktop", while the IDXGIOutput1 interface is
available for all API subsets.
This fixes compilation for UWP/"Windows Store" configurations (and
older API subsets like Windows Phone).
Signed-off-by: Martin Storsjö <martin@martin.st>
Handling this in general code makes more sense than handling it in
individual codec files, because it would be a lot of unnecessary code
duplication for the plenty of formats that support exporting ICC
profiles (jpg, png, tiff, webp, jxl, ...).
encode.c and decode.c will be in charge of initializing this state as
needed, so we merely need to make sure to uninit it afterwards from the
common destructor path.
Signed-off-by: Niklas Haas <git@haasn.dev>
pkg_config fallback for SDL2 use 2.1.0 as max (excluded) version
where the pkg_config specify 3.0.0
Correcting fallback version to be in line with the pkg_config version
Signed-off-by: dvhh <dvhh@yahoo.com>
Signed-off-by: Marton Balint <cus@passwd.hu>
This simplifies the code to no longer have #ifs in a manner which
does not require handling avpriv_ac3_parse_header returning ENOSYS.
As an existing example, the MPEG-TS muxer already requires the AC-3
parser, and in order to fix existing issues with the current AC-3
movenc code, switching to use the AC-3 parser is required, so this
is an enabling change for that.
Signed-off-by: Jan Ekström <jan.ekstrom@24i.com>
Support for VDPAU accelerated AV1 decoding was added with libvdpau-1.5.
Support for the same in ffmpeg is added with this patch. Profiles
related to VDPAU AV1 can be found in latest vdpau.h present in
libvdpau-1.5.
Add AV1 VDPAU to list of hwaccels and supported formats
Added file vdpau_av1.c and Modified configure to add VDPAU AV1 support.
Mapped AV1 profiles to VDPAU AV1 profiles. Populated the codec specific
params that need to be passed to VDPAU.
Signed-off-by: Philip Langdale <philipl@overt.org>
wchartoutf8() converts strings returned by WinAPI into UTF-8,
which is FFmpeg's preffered encoding.
Some external dependencies, such as AviSynth, are still
not Unicode-enabled. utf8toansi() converts UTF-8 strings
into ANSI in two steps: UTF-8 -> wchar_t -> ANSI.
wchartoansi() is responsible for the second step of the conversion.
Conversion in just one step is not supported by WinAPI.
Since these character converting functions allocate the buffer
of necessary size, they also facilitate the removal of MAX_PATH limit
in places where fixed-size ANSI/WCHAR strings were used
as filename buffers.
On Windows, getenv_utf8() wraps _wgetenv() converting its input from
and its output to UTF-8. Strings returned by getenv_utf8()
must be freed by freeenv_utf8().
On all other platforms getenv_utf8() is a wrapper around getenv(),
and freeenv_utf8() is a no-op.
The value returned by plain getenv() cannot be modified;
av_strdup() is usually used when modifications are required.
However, on Windows, av_strdup() after getenv_utf8() leads to
unnecessary allocation. getenv_dup() is introduced to avoid
such an allocation. Value returned by getenv_dup() must be freed
by av_free().
Because of cleanup complexities, in places that only test the existence
of an environment variable or compare its value with a string
consisting entirely of ASCII characters, the use of plain getenv()
is still preferred. (libavutil/log.c check_color_terminal()
is an example of such a place.)
Plain getenv() is also preffered in UNIX-only code,
such as bktr.c, fbdev_common.c, oss.c in libavdevice
or af_ladspa.c in libavfilter.
Signed-off-by: Martin Storsjö <martin@martin.st>
Was "[PATCH] libx264: Do not explicitly set X264_API_IMPORTS"
Setting X264_API_IMPORTS only affects msvc builds and it breaks
linking to static builds (although is required for shared builds).
This flag is set by x264 in its pkgconfig as required since build
158 (a615f027ed172e2dd5380e736d487aa858a0c4ff) from July 2019.
So this patch updates configure to require a newer x264 build that
correctly sets the imports flag.
The min version requirement of 158 is applied for msvc builds only.
This is also removing the check for 'libx264 without pkg-config'
which was left for compatibility reasons about 7 years ago when
the pkg-config check was introduced by commit
e06263ef1e.
Co-authored-by: softworkz <softworkz@hotmail.com>
Signed-off-by: softworkz <softworkz@hotmail.com>
Signed-off-by: Matt Oliver <protogonoi@gmail.com>
Signed-off-by: Marton Balint <cus@passwd.hu>
This fixed the regression caused by commit 478e1a98a
Reported-by: Timo Rothenpieler <timo@rothenpieler.org>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
Allows non-UWP builds of FFmpeg with MediaFoundation to work on
N editions of Windows which are without MediaFoundation by default.
On UWP target, FFmpeg is linked directly against MediaFoundation since
LoadLibrary is not available.
This commit adresses https://trac.ffmpeg.org/ticket/9788
Signed-off-by: Martin Storsjö <martin@martin.st>
libmfx 1.28 was released 3 years ago, it is easy to get a greater
version than 1.28. We may remove lots of compile-time checks if adding
the requirement for the minimal version in the configure script.
Reviewed-by: softworkz <softworkz@hotmail.com>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
Add an AVIF muxer by re-using the existing the mov/mp4 muxer.
AVIF Specification: https://aomediacodec.github.io/av1-avif
Sample usage for still image:
ffmpeg -i image.png -c:v libaom-av1 -still-picture 1 image.avif
Sample usage for animated AVIF image:
ffmpeg -i video.mp4 animated.avif
We can re-use any of the AV1 encoding options that will make
sense for image encoding (like bitrate, tiles, encoding speed,
etc).
The files generated by this muxer has been verified to be valid
AVIF files by the following:
1) Displays on Chrome (both still and animated images).
2) Displays on Firefox (only still images, firefox does not support
animated AVIF yet).
3) Verified to be valid by Compliance Warden:
https://github.com/gpac/ComplianceWarden
Fixes the encoder/muxer part of Trac Ticket #7621
Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
sdl2 recently changed their versioning, moving the patch level to minor level
cd7c2f1de7
and have said that they will instead ship sdl3.pc for 3.0.0
Fixes ticket 9768
Signed-off-by: Christopher Degawa <ccom@randomderp.com>
Signed-off-by: Gyan Doshi <ffmpeg@gyani.pro>
This filter is designed to parse embedded ICC profiles and attempt
extracting colorspace tags from them, updating the AVFrame metadata
accordingly.
This is intentionally made a separate filter, rather than being part of
libavcodec itself, so that it's an opt-in behavior for the time being.
This also gives the user more flexibility to e.g. first attach an ICC
profile and then also set the colorspace tags from it.
This makes #9673 possible, though not automatic.
Signed-off-by: Niklas Haas <git@haasn.dev>
This filter is designed to specifically cover the task of generating ICC
profiles (and attaching them to output frames) on demand. Other tasks,
such as ICC profile loading/stripping, or ICC profile application, are
better left to separate filters (or included into e.g. vf_setparams).
Signed-off-by: Niklas Haas <git@haasn.dev>
This introduces an optional dependency on lcms2 into FFmpeg. lcms2 is a
widely used library for ICC profile handling, which apart from being
used in almost all major image processing programs and video players,
has also been deployed in browsers. As such, it's both widely available
and well-tested.
Add a few helpers to cover our major use cases. This commit merely
introduces the helpers (and configure check), even though nothing uses
them yet.
It's worth pointing out that the reason the cmsToneCurves for each
AVCOL_TRC are cached inside the context, is because constructing a
cmsToneCurve requires evaluating the curve at 4096 (by default) grid
points and constructing a LUT. So, we ideally only want to do this once
per curve. This matters for e.g. ff_icc_profile_detect_transfer, which
essentially compares a profile against all of these generated LUTs.
Re-generating the LUTs for every iteration would be unnecessarily
wasteful.
The same consideration does not apply to e.g. cmsCreate*Profile, which
is a very lightweight operation just involving struct allocation and
setting a few pointers.
The cutoff value of 0.01 was determined by experimentation. The lowest
"false positive" delta I saw in practice was 0.13, and the largest
"false negative" delta was 0.0008. So a value of 0.01 sits comfortaby
almost exactly in the middle.
Signed-off-by: Niklas Haas <git@haasn.dev>
