------------------------------------
x265 version history
------------------------------------

Version 2.8
===========

Release date - 21/05/2018

New features
------------
1. `--asm avx512` used to enable AVX-512 in x265. Default disabled. For 4K main10 high-quality encoding, we are seeing good gains; for other resolutions and presets, we don’t recommend using this setting for now.
2. `--dynamic-refine` dynamically switches between different inter refine levels. Default disabled. It is recommended to use :option:`–refine-intra 4’ with dynamic refinement for a better trade-off between encode efficiency and performance than using static refinement.
3. `--single-sei`: Encode SEI messages in a single NAL unit instead of multiple NAL units. Default disabled.
4. `--max-ausize-factor` controls the maximum AU size defined in HEVC specification. It represents the percentage of maximum AU size used. Default is 1.
5. VMAF (Video Multi-Method Assessment Fusion) Added VMAF support for objective quality measurement of a video sequence. Enable cmake option ENABLE_LIBVMAF to report per frame and aggregate VMAF score. The frame level VMAF score does not include temporal scores. This is supported only on linux for now.

Encoder enhancements
--------------------
1. Introduced refine-intra level 4 to improve quality.
2. Support for HLG-graded content and pic_struct in SEI message.

Bug Fixes
---------
1. Fix 32 bit build error (using CMAKE GUI) in Linux.
2. Fix 32 bit build error for asm primitives.
3. Fix build error on mac OS.
4. Fix VBV Lookahead in analysis load to achieve target bitrate.


Version 2.7
===========

Release date - 21st Feb, 2018.

New features
------------
1. `--gop-lookahead` can be used to extend the gop boundary(set by `--keyint`). The GOP will be extended, if a scene-cut frame is found within this many number of frames. 
2. Support for RADL pictures added in x265. `--radl` can be used to decide number of RADL pictures preceding the IDR picture.

Encoder enhancements
--------------------
1. Moved from YASM to NASM assembler. Supports NASM assembler version 2.13 and greater.
2. Enable analysis save and load in a single run. Introduces two new cli options `--analysis-save <filename>` and `--analysis-load <filename>`.
3. Comply to HDR10+ LLC specification.
4. Reduced x265 build time by more than 50% by re-factoring ipfilter.asm.  

Bug fixes
---------
1. Fixed inconsistent output issue in deblock filter and --const-vbv.
2. Fixed Mac OS build warnings.
3. Fixed inconsistency in pass-2 when weightp and cutree are enabled.
4. Fixed deadlock issue due to dropping of BREF frames, while forcing slice types through qp file.


Version 2.6
===========

Release date - 29th November, 2017.

New features
------------
1. x265 can now refine analysis from a previous HEVC encode (using options :option:`--refine-inter`, and :option:`--refine-intra`), or a previous AVC encode (using option :option:`--refine-mv-type`). The previous encode's information can be packaged using the *x265_analysis_data_t*  data field available in the *x265_picture* object.
2. Basic support for segmented (or chunked) encoding added with :option:`--vbv-end` that can specify the status of CPB at the end of a segment. String this together with :option:`--vbv-init` to encode a title as chunks while maintaining VBV compliance!
3. :option:`--force-flush` can be used to trigger a premature flush of the encoder. This option is beneficial when input is known to be bursty, and may be at a rate slower than the encoder.
4. Experimental feature :option:`--lowpass-dct` that uses truncated DCT for transformation.

Encoder enhancements
--------------------
1. Slice-parallel mode gets a significant boost in performance, particularly in low-latency mode.
2. x265 now officially supported on VS2017.
3. x265 now supports all depths from mono0 to mono16 for Y4M format.

API changes
-----------
1. Options that modified PPS dynamically (:option:`--opt-qp-pps` and :option:`--opt-ref-list-length-pps`) are now disabled by default to enable users to save bits by not sending headers. If these options are enabled, headers have to be repeated for every GOP.
2. Rate-control and analysis parameters can dynamically be reconfigured simultaneously via the *x265_encoder_reconfig* API.
3. New API functions to extract intermediate information such as slice-type, scenecut information, reference frames, etc. are now available. This information may be beneficial to integrating applications that are attempting to perform content-adaptive encoding. Refer to documentation on *x265_get_slicetype_poc_and_scenecut*, and *x265_get_ref_frame_list* for more details and suggested usage.
4. A new API to pass supplemental CTU information to x265 to influence analysis decisions has been added. Refer to documentation on *x265_encoder_ctu_info* for more details.

Bug fixes
---------
1. Bug fixes when :option:`--slices` is used with VBV settings.
2. Minor memory leak fixed for HDR10+ builds, and default x265 when pools option is specified.
3. HDR10+ bug fix to remove dependence on poc counter to select meta-data information.


Version 2.5
===========

Encoder enhancements
--------------------
1. Improved grain handling with :option:`--tune` grain option by throttling VBV operations to limit QP jumps.
2. Frame threads are now decided based on number of threads specified in the :option:`--pools`, as opposed to the number of hardware threads available. The mapping was also adjusted to improve quality of the encodes with minimal impact to performance.
3. CSV logging feature (enabled by :option:`--csv`) is now part of the library; it was previously part of the x265 application. Applications that integrate libx265 can now extract frame level statistics for their encodes by exercising this option in the library.
4.  Globals that track min and max CU sizes, number of slices, and other parameters have now been moved into instance-specific variables. Consequently, applications that invoke multiple instances of x265 library are no longer restricted to use the same settings for these parameter options across the multiple instances.
5. x265 can now generate a seprate library that exports the HDR10+ parsing API. Other libraries that wish to use this API may do so by linking against this library. Enable ENABLE_HDR10_PLUS in CMake options and build to generate this library.
6. SEA motion search receives a 10% performance boost from AVX2 optimization of its kernels.
7. The CSV log is now more elaborate with additional fields such as PU statistics, average-min-max luma and chroma values, etc. Refer to documentation of :option:`--csv` for details of all fields.
8. x86inc.asm cleaned-up for improved instruction handling.

API changes
-----------
1. New API x265_encoder_ctu_info() introduced to specify suggested partition sizes for various CTUs in a frame. To be used in conjunction with :option:`--ctu-info` to react to the specified partitions appropriately.
2. Rate-control statistics passed through the x265_picture object for an incoming frame are now used by the encoder.
3. Options to scale, reuse, and refine analysis for incoming analysis shared through the x265_analysis_data field in x265_picture for runs that use :option:`--analysis-reuse-mode` load; use options :option:`--scale`, :option:`--refine-mv`, :option:`--refine-inter`, and :option:`--refine-intra` to explore. 
4. VBV now has a deterministic mode. Use :option:`--const-vbv` to exercise.

Bug fixes
---------
1. Several fixes for HDR10+ parsing code including incompatibility with user-specific SEI, removal of warnings, linking issues in linux, etc.
2. SEI messages for HDR10 repeated every keyint when HDR options (:option:`--hdr-opt`, :option:`--master-display`) specified.


Version 2.4
===========

Encoder enhancements
----------------------------------
1. HDR10+ supported. Dynamic metadata may be either supplied as a bitstream via the userSEI field of x265_picture, or as a json jile that can be parsed by x265 and inserted into the bitstream; use --dhdr10-info to specify json file name, and --dhdr10-opt to enable optimization of inserting tone-map information only at IDR frames, or when the tone map information changes.
2. Lambda tables for 8, 10, and 12-bit encoding revised, resulting in significant enhancement to subjective visual quality.
3. Enhanced HDR10 encoding with HDR-specific QP optimzations for chroma, and luma planes of WCG content enabled; use --hdr-opt to activate.
4. Ability to accept analysis information from other previous encodes (that may or may not be x265), and selectively reuse and refine analysis for encoding subsequent passes enabled with the --refine-level option.
5. Slow and veryslow presets receive a 20% speed boost at iso-quality by enabling the --limit-tu option.
6. The bitrate target for x265 can now be dynamically reconfigured via the reconfigure API.
7. Performance optimized SAO algorithm introduced via the --limit-sao option; seeing 10% speed benefits at faster presets.

API changes
-------------------
1. x265_reconfigure API now also accepts rate-control parameters for dynamic reconfiguration.
2. Several additions to data fields in x265_analysis to support --refine-level: see x265.h for more details.

Bug fixes
--------------
1. Avoid negative offsets in x265 lambda2 table with SAO enabled.
2. Fix mingw32 build error.
3. Seek now enabled for pipe input, in addition to file-based input
4. Fix issue of statically linking core-utils not working in linux.
5. Fix visual artifacts with --multi-pass-opt-distortion with VBV.
6. Fix bufferFill stats reported in csv.


Version 2.3
===========

Encoder enhancements
----------------------------------
1. New SSIM-based RD-cost computation for improved visual quality, and efficiency; use --ssim-rd to exercise.
2. Multi-pass encoding can now share analysis information from prior passes (in addition to rate-control information) to improve performance and quality of subsequent passes; to your multi-pass command-lines that use the --pass option, add --multi-pass-opt-distortion to share distortion information, and --multi-pass-opt-analysis to share other analysis information.
3. A dedicated thread pool for lookahead can now be specified with --lookahead-threads.
4. option:–dynamic-rd dynamically increase analysis in areas where the bitrate is being capped by VBV; works for both CRF and ABR encodes with VBV settings.
5. The number of bits used to signal the delta-QP can be optimized with the --opt-cu-delta-qp option; found to be useful in some scenarios for lower bitrate targets.
6. Experimental feature option:–aq-motion adds new QP offsets based on relative motion of a block with respect to the movement of the frame.

API changes
-------------------
1. Reconfigure API now supports signalling new scaling lists.
2. x265 application’s csv functionality now reports time (in milliseconds) taken to encode each frame.
3. --strict-cbr enables stricter bitrate adherence by adding filler bits when achieved bitrate is lower than the target; earlier, it was only reacting when the achieved rate was higher.
4. --hdr can be used to ensure that max-cll and max-fall values are always signaled (even if 0,0).

Bug fixes
--------------
1. Fixed incorrect HW thread counting on MacOS platform.
2. Fixed scaling lists support for 4:4:4 videos.
3. Inconsistent output fix for --opt-qp-pss by removing last slice’s QP from cost calculation.
4. VTune profiling (enabled using ENABLE_VTUNE CMake option) now also works with 2017 VTune builds.


Version 2.2
===========

Encoder enhancements
----------------------------------
1. Enhancements to TU selection algorithm with early-outs for improved speed; use --limit-tu to exercise.
2. New motion search method SEA (Successive Elimination Algorithm) supported now as –me 4
3. Bit-stream optimizations to improve fields in PPS and SPS for bit-rate savings through --[no-]opt-qp-pps, --[no-]opt-ref-list-length-pps, and --[no-]multi-pass-opt-rps.
4. Enabled using VBV constraints when encoding without WPP.
5. All param options dumped in SEI packet in bitstream when info selected.
6. x265 now supports POWERPC-based systems. Several key functions also have optimized ALTIVEC kernels.

API changes
-------------------
1. Options to disable SEI and optional-VUI messages from bitstream made more descriptive.
2. New option --scenecut-bias to enable controlling bias to mark scene-cuts via cli.
3. Support mono and mono16 color spaces for y4m input.
4. --min-cu-size of 64 no-longer supported for reasons of visual quality (was crashing earlier anyways.)
5. API for CSV now expects version string for better integration of x265 into other applications.

Bug fixes
--------------
1. Several fixes to slice-based encoding.
2. --log2-max-poc-lsb‘s range limited according to HEVC spec.
3. Restrict MVs to within legal boundaries when encoding.


Version 2.1
===========

Release date - 27th September, 2016

Encoder enhancements
--------------------
1. Support for qg-size of 8
2. Support for inserting non-IDR I-frames at scenecuts and when running with settings for fixed-GOP (min-keyint = max-keyint)
3. Experimental support for slice-parallelism.

API changes
-----------
1. Encode user-define SEI messages passed in through x265_picture object.
2. Disable SEI and VUI messages from the bitstream
3. Specify qpmin and qpmax
4. Control number of bits to encode POC.

Bug fixes
---------
1. QP fluctuation fix for first B-frame in mini-GOP for 2-pass encoding with tune-grain.
2. Assembly fix for crashes in 32-bit from dct_sse4.
3. Threadpool creation fix in windows platform.


Version 2.0
===========

Release date - 13th July, 2016

New Features
------------

1. uhd-bd: Enable Ultra-HD Bluray support
2. rskip: Enables skipping recursion to analyze lower CU sizes using heuristics at different rd-levels. Provides good visual quality gains at the highest quality presets. 
3. rc-grain: Enables a new ratecontrol mode specifically for grainy content. Strictly prevents QP oscillations within and between frames to avoid grain fluctuations.
4. tune grain: A fully refactored and improved option to encode film grain content including QP control as well as analysis options.
5. asm: ARM assembly is now enabled by default, native or cross compiled builds supported on armv6 and later systems.

API and Key Behaviour Changes
-----------------------------

1. x265_rc_stats added to x265_picture, containing all RC decision points for that frame
2. PTL: high tier is now allowed by default, chosen only if necessary
3. multi-pass: First pass now uses slow-firstpass by default, enabling better RC decisions in future passes 
4. pools: fix behaviour on multi-socketed Windows systems, provide more flexibility in determining thread and pool counts
5. ABR: improve bits allocation in the first few frames, abr reset, vbv and cutree improved

Misc
----
1. An SSIM calculation bug was corrected


Version 1.9
===========

Release date - 29th January, 2016

New Features
------------

1. Quant offsets: This feature allows block level quantization offsets to be specified for every frame. An API-only feature.
2. --intra-refresh: Keyframes can be replaced by a moving column of intra blocks in non-keyframes.
3. --limit-modes: Intelligently restricts mode analysis. 
4. --max-luma and --min-luma for luma clipping, optional for HDR use-cases
5. Emergency denoising is now enabled by default in very low bitrate, VBV encodes

API Changes
-----------

1. x265_frame_stats returns many additional fields: maxCLL, maxFALL, residual energy, scenecut  and latency logging
2. --qpfile now supports frametype 'K"
3. x265 now allows CRF ratecontrol in pass N (N greater than or equal to 2)
4. Chroma subsampling format YUV 4:0:0 is now fully supported and tested

Presets and Performance
-----------------------

1. Recently added features lookahead-slices, limit-modes, limit-refs have been enabled by default for applicable presets.
2. The default psy-rd strength has been increased to 2.0
3. Multi-socket machines now use a single pool of threads that can work cross-socket.


Version 1.8
===========

Release date - 10th August, 2016

API Changes
-----------
1. Experimental support for Main12 is now enabled. Partial assembly support exists. 
2. Main12 and Intra/Still picture profiles are now supported. Still picture profile is detected based on x265_param::totalFrames.
3. Three classes of encoding statistics are now available through the API. 
a) x265_stats - contains encoding statistics, available through x265_encoder_get_stats()
b) x265_frame_stats and x265_cu_stats - contains frame encoding statistics, available through recon x265_picture
4. --csv
a) x265_encoder_log() is now deprecated
b) x265_param::csvfn is also deprecated
5. --log-level now controls only console logging, frame level console logging has been removed.
6. Support added for new color transfer characteristic ARIB STD-B67

New Features
------------
1. limit-refs: This feature limits the references analysed for individual CUS. Provides a nice tradeoff between efficiency and performance.
2. aq-mode 3: A new aq-mode that provides additional biasing for low-light conditions.
3. An improved scene cut detection logic that allows ratecontrol to manage visual quality at fade-ins and fade-outs better.

Preset and Tune Options
-----------------------

1. tune grain: Increases psyRdoq strength to 10.0, and rdoq-level to 2.
2. qg-size: Default value changed to 32.


Version 1.7
===========

x265 version 1.7 has been released. This release contains a large amount of assembly code optimizations, some preliminary support for high dynamic range content, improvements for multi-library support, and some new quality features.

Full documentation at: http://x265.readthedocs.org/en/1.7/

This release simplifies the multi-library support introduced in version 1.6. Any libx265 can now forward API requests to other installed libx265 libraries (by name) so applications like ffmpeg and the x265 CLI can select between 8bit and 10bit encodes at runtime without the need of a shim library or library load path hacks. See --output-depth, and http://x265.readthedocs.org/en/1.7/a...rary-interface

For quality, x265 now allows you to configure the quantization group size smaller than the CTU size (for finer grained AQ adjustments). See --qg-size.

x265 now supports limited mid-encode reconfigure via a new public method: x265_encoder_reconfig()

For HDR, x265 now supports signaling the SMPTE 2084 color transfer function, the SMPTE 2086 mastering display color primaries, and the content light levels. See --master-display, --max-cll

x265 will no longer emit any non-conformant bitstreams unless --allow-non-conformance is specified.

The x265 CLI now supports a simple encode preview feature. See --recon-y4m-exec.

The AnnexB NAL headers can now be configured off, via x265_param.bAnnexB This is not configurable via the CLI because it is a function of the muxer being used, and the CLI only supports raw output files. See --annexb

Misc:
* --lossless encodes are now signaled as level 8.5
* --profile now has a -P short option
* The regression scripts used by x265 are now public, and can be found at: https://bitbucket.org/sborho/test-harness
* x265's cmake scripts now support PGO builds, the test-harness can be used to drive the profile-guided build process. 


Version 1.6
===========

x265 1.6 has been released. The changes from the 1.5 release are mostly performance oriented, with heavy improvements for AVX2 capable platforms (Haswell and later Intel CPUs) and work efficiency improvements for multiple-socket machines.

API changes
------------

--threads N replaced by --pools N,N and --lookahead-slices N --[no-]rdoq-level N - finer control over RDOQ effort --min-cu-size N - trade-off compression for performance --max-tu-size N - trade-off compression for performance --[no-]temporal-layers - code unreferenced B frames in temporal layer 1 --[no-]cip aliases added for --[no-]constrained-intra

Added support for new color transfer functions "smpte-st-2084" and "smpte-st-428

--limit-refs N was added, but not yet implemented

Deprecated x265_setup_primitives() was removed from the public API and is no longer exported DLLs

See the online documentation for full descriptions:

http://x265.readthedocs.org/en/1.6/

Threading changes
-----------------

The x265 thread pool has been made NUMA aware. The --threads parameter, which used to specify a global pool size, has been replaced with a --pools parameter which allows you to specify a pool size per NUMA node (aka CPU socket or package). The default is still to allocate one pool worker thread per logical core on the machine, but with --pools one can isolate those threads to a given socket.

Other than socket isolation, the biggest visible change in the NUMA aware thread pools is the increase in work efficiency. The total utilization will generally decrease but the performance will increase since worker threads spend less time context switching. Also, the threading of the lookahead was made more work-efficient. Each lookahead job is a much larger piece of work.

Before (1.5):

disable thread pool: --threads 1
default thread pool: --threads 0
restrict to 4 threads: --threads 4

After (1.6):

disable thread pools: --pools 0
default thread pools: --pools *
restrict to 4 threads: --pools 4
restrict to 4 threads on socket 1: --pools -,4 restrict to all threads on socket 0: --pools +,-

Multi-lib interface
-------------------

In order to support runtime selection of a libx265 shared library, we have introduced an x265_api structure and an x265_api_get() function.
Applications which use this interface to acquire the libx265 functional interface will be able to use shim libraries to bind a particular build of libx265 at run time. See the API documentation for full details. 


Version 1.4
===========

x265 1.4 is a regularly scheduled release, mostly focused on performance
enhancements. There was a large refactor of the analysis code that
exposed further parallelism without sacraficing any compression
efficiency. In general, 1.4 should have slightly better compression
efficiency than 1.3 for the same encodes.

The refactors also generally lowered the memory requirements and made
the faster presets more compute efficient.

The two most important new features are --pmode (parallel mode decision)
and --pme (parallel motion estimation).

= --pmode : param.bDistributeModeAnalysis =

This feature will distribute mode analysis for each CU. The more modes
that must be analyzed, the more effective this feature becomes. So the
slow preset that enables rectangular prediction modes benefits from
pmode more than medium preset, and the slower modes which use RD level
6 benefit from pmode even more since they enable AMP predictions and
evaluate the rate distortion cost of each mode.

The output of --pmode encodes should have slightly better compression
than those with it disabled, since certain early outs are impossible
with --pmode and thus all modes are measured naievely.

= --pme : param.bDistributeMotionEstimation =

This feature will distribute the motion estimations for each CU that has
more than 2 references. Its effectiveness is proportional to the number
of references, but this feature can often be a net performance loss as
the overhead of involving other CPU cores is often more expensive than
the parallelism benefit.

The output of the encode is completely unaffected by --pme.

Both --pme and --pmode are only useful when x265 is otherwise unable to
fully saturate the CPU cores, and both can also at times result in lower
performance on multi-socket machines (depending on the situation) since
we are not yet keeping work localized to neighbor CPUs.

= Also in 1.4 =

As a result of the refactor work, none of the original HM classes or
source files remain in x265.

Temporal motion vector predictions (previously hard-coded to always be
enabled) are now runtime selectable (param.bEnableTemporalMvp) but still
default to being enabled in all presets.

Frame based SAO analysis was removed (frame based SAO signaling did not
make it into the final HEVC spec), and --sao-lcu-bounds=<0|1> was
renamed to --[no-]sao-non-deblock (param.bSaoNonDeblocked)

Some inconsistencies in the analysis logic were fixed. --amp is now
respected in RD levels 2, 3, and 4 (previously only in 5 and 6).
--b-intra is now respected in all RD levels. --fast-cbf, which has only
ever effective at RD levels 5 and 6, is no longer enabled uselessly in
the fastest presets.

--weightb is now enabled by default at presets slower, veryslow, and
placebo.

--cu-lossless was changed to only attempt a lossless encode of the best
lossy encode method. This made --cu-lossless a much less expensive
encode option to have enabled, and hopefully made the feature more
robust and maintainable.

The upper threshold for --psy-rdoq was raised to 50 (from 10) since the
higher values were found to be beneficial for sources with high
frequency noise (film grain).

The default thread pool size logic was updated to account for the
addition of --pmode and --pme (if WPP is disabled but --pmode or --pme
are enabled, a thread pool is still allocated).

In 1.4 there also appeared an incomplete analysis re-use feature. This
will be completed and further improved in the coming weeks.
