Release date - 16th March, 2021.
- Real-time VBV for ABR (Average BitRate) encodes in –pass 2 using
--vbv-live-multi-pass: Improves VBV compliance with no significant impact on coding efficiency.
Enhancements to existing features¶
- Improved hist-based scene cut algorithm: Reduces false positives by leveraging motion and scene transition info.
- Support for RADL pictures at IDR scene cuts: Improves coding efficiency with no significant impact on performance.
- Bidirectional scene cut aware Frame Quantizer Selection: Saves bits than forward masking with no noticeable perceptual quality difference.
Release date - 29th May, 2020.
- Edge-aware quadtree partitioning to terminate CU depth recursion based on edge information.
--rskiplevel 2 enables the feature and
--rskip-edge-thresholddenotes the minimum expected edge-density percentage within the CU, below which the recursion is skipped. Experimental feature.
- Application-level feature
--abr-ladderfor automating efficient ABR ladder generation. Shows ~65% savings in the over-all turn-around time required for the generation of a typical Apple HLS ladder in Intel(R) Xeon(R) Platinum 8280 CPU @ 2.70GHz over a sequential ABR-ladder generation approach that leverages save-load architecture.
Enhancements to existing features¶
- Improved efficiency in 2-pass rate-control algorithm. The savings in the bitrate is ~1.72% with visual improvement in quality in the initial 1-2 secs.
- Faster ARM64 encodes enabled by ASM contributions from Huawei. The speed-up over no-asm version for 1080p encodes @ medium preset is ~15% in a 16 core H/W.
- Strict VBV conformance in zone encoding.
Release date - 17th February, 2020.
- Adaptive frame duplication to identify and skip encoding of near-identical frames and signal the duplication info to the decoder via pic_struct SEI.
frame-dupto enable frame duplication and
--dup-thresholdto set the threshold for frame similarity (optional).
- Boundary aware quantization to cut off bits from frames following scene-cut. This leverages the inability of HVS to perceive fine details during scene changes and saves bits.
--max-qp-deltato enable boundary aware frame quantization, to set window size (optional) and to set QP offset (optional).
- Improved scene-cut detection using edge and chroma histograms.
--hist-scenecutto enable the feature and
--hist-threshold(optional) to provide threshold for determining scene cuts.
Enhancements to existing features¶
--hme-rangeto modify search range for HME levels L0, L1, and L2.
- Improved performance of AQ mode 4 by reducing memory foot print.
--analysis-load-reuse-levelto de-couple reuse levels of
--analysis-load. Turnaround time of ABR encoding can be reduced by properly leveraging these options.
- Improved VBV lookahead to eliminate blocky artifacts in Intra frames coming towards end of the title.
- New API function x265_encoder_reconfig_zone() to invoke zone reconfiguration dynamically.
--hdrwill be deprecated in the upcoming major release.
--hdr-optwill be deprecated in the upcoming major release.
- Additions to x265_param structure to support the newly added features and encoder enhancements.
Release date - 25th September, 2019.
- Improved quality in the frames following dark scenes in ABR mode.
- Fixed encoder crash with
--zonefileduring failures in encoder_open().
- Fixed JSON11 build errors with HDR10+ on MacOS high sierra.
- Signalling out of range scaling list data fixed.
- Inconsistent output fix for 2-pass rate-control with cutree ON.
- Build dependency on changeset cf37911 of SVT-HEVC.
Release date - 18th June, 2019.
- x265 can invoke SVT-HEVC library for encoding through
- x265 can now accept interlaced inputs directly (no need to separate fields), and sends it to the encoder with proper fps and frame-size through
--fadescan detect and handle fade-in regions. This option will force I-slice and initialize RC history for the brightest frame after fade-in.
- A new flag to signal MasterDisplayParams and maxCll/Fall separately
- Improved the performance of inter-refine level 1 by skipping the evaluation of smaller CUs when the current block is decided as “skip” by the save mode.
- New AVX2 primitives to improve the performance of encodes that enable
- Improved performance in medium preset with negligible loss in quality.
- Bug fixes for zones.
- Fixed wrap-around from MV structure overflow occurred around 8K pixels or over.
- Fixed issues in configuring cbQpOffset and crQpOffset for 444 input
- Fixed cutree offset computation in 2nd pass encodes.
- AVX512 main12 asm disabling.
- Inconsistent output with 2-pass due to cutree offset sharing.
Release date - 23/01/2019
- option:: ‘–dolby-vision-profile <integer|float>’ generates bitstreams confirming to the specified Dolby Vision profile. Currently profile 5, profile 8.1 and profile 8.2 enabled, Default 0 (disabled)
- option:: ‘–dolby-vision-rpu’ File containing Dolby Vision RPU metadata. If given, x265’s Dolby Vision metadata parser will fill the RPU field of input pictures with the metadata
- read from the file. The library will interleave access units with RPUs in the bitstream. Default NULL (disabled).
- option:: ‘–zonefile <filename>’ specifies a text file which contains the boundaries of the zones where each of zones are configurable.
- option:: ‘–qp-adaptation-range’ Delta-QP range by QP adaptation based on a psycho-visual model. Default 1.0.
- option:: ‘–refine-ctu-distortion <0/1>’ store/normalize ctu distortion in analysis-save/load. Default 0.
- Experimental feature option:: ‘–hevc-aq’ enables adaptive quantization
- It scales the quantization step size according to the spatial activity of one coding unit relative to frame average spatial activity. This AQ method utilizes the minimum variance of sub-unit in each coding unit to represent the coding unit’s spatial complexity.
- Preset: change param defaults for veryslow and slower preset. Replace slower preset with defaults used in veryslow preset and change param defaults in veryslow preset as per experimental results.
- AQ: change default AQ mode to auto-variance
- Cutree offset reuse: restricted to analysis reuse-level 10 for analysis-save -> analysis-load
- Tune: introduce –tune animation option which improves encode quality for animated content
- Reuse CU depth for B frame and allow I, P frame to follow x265 depth decision
- RC: fix rowStat computation in const-vbv
- Dynamic-refine: fix memory reset size.
- Fix Issue #442: linking issue on non x86 platform
- Encoder: Do not include CLL SEI message if empty
- Fix issue #441 build error in VMAF lib
Release date - 05/10/2018
Support for chunked encoding
--chunk-start and --chunk-endFrames preceding first frame of chunk in display order will be encoded, however, they will be discarded in the bitstream. Frames following last frame of the chunk in display order will be used in taking lookahead decisions, but, they will not be encoded. This feature can be enabled only in closed GOP structures. Default disabled.
Support for HDR10+ version 1 SEI messages.
- Create API function for allocating and freeing x265_analysis_data.
- CEA 608/708 support: Read SEI messages from text file and encode it using userSEI message.
- Disable noise reduction when vbv is enabled.
- Support minLuma and maxLuma values changed by the commandline.
Release date - 21/05/2018
--asm avx512used 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.
- Encode SEI messages in a single NAL unit instead of multiple NAL units. Default disabled.
--max-ausize-factorcontrols the maximum AU size defined in HEVC specification.
- It represents the percentage of maximum AU size used. Default is 1.
- 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.
- Introduced refine-intra level 4 to improve quality.
- Support for HLG-graded content and pic_struct in SEI message.
- Fix 32 bit build error (using CMAKE GUI) in Linux.
- Fix 32 bit build error for asm primitives.
- Fix build error on mac OS.
- Fix VBV Lookahead in analysis load to achieve target bitrate.
Release date - 21st Feb, 2018.
- Moved from YASM to NASM assembler. Supports NASM assembler version 2.13 and greater.
- Enable analysis save and load in a single run. Introduces two new cli options –analysis-save <filename> and –analysis-load <filename>.
- Comply to HDR10+ LLC specification.
- Reduced x265 build time by more than 50% by re-factoring ipfilter.asm.
- Fixed inconsistent output issue in deblock filter and –const-vbv.
- Fixed Mac OS build warnings.
- Fixed inconsistency in pass-2 when weightp and cutree are enabled.
- Fixed deadlock issue due to dropping of BREF frames, while forcing slice types through qp file.
Release date - 29th November, 2017.
- x265 can now refine analysis from a previous HEVC encode (using options
--refine-intra), or a previous AVC encode (using 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.
- Basic support for segmented (or chunked) encoding added with
--vbv-endthat can specify the status of CPB at the end of a segment. String this together with
--vbv-initto encode a title as chunks while maintaining VBV compliance!
--force-flushcan 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.
- Experimental feature
--lowpass-dctthat uses truncated DCT for transformation.
- Slice-parallel mode gets a significant boost in performance, particularly in low-latency mode.
- x265 now officially supported on VS2017.
- x265 now supports all depths from mono0 to mono16 for Y4M format.
- Options that modified PPS dynamically (
--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.
- Rate-control and analysis parameters can dynamically be reconfigured simultaneously via the x265_encoder_reconfig API.
- 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.
- 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.
Release date - 13th July, 2017.
- Improved grain handling with
--tunegrain option by throttling VBV operations to limit QP jumps.
- Frame threads are now decided based on number of threads specified in the
--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.
- CSV logging feature (enabled by
--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.
- 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.
- 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.
- SEA motion search receives a 10% performance boost from AVX2 optimization of its kernels.
- 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
--csvfor details of all fields.
- x86inc.asm cleaned-up for improved instruction handling.
- New API x265_encoder_ctu_info() introduced to specify suggested partition sizes for various CTUs in a frame. To be used in conjunction with
--ctu-infoto react to the specified partitions appropriately.
- Rate-control statistics passed through the x265_picture object for an incoming frame are now used by the encoder.
- Options to scale, reuse, and refine analysis for incoming analysis shared through the x265_analysis_data field in x265_picture for runs that use
--analysis-reuse-modeload; use options
- VBV now has a deterministic mode. Use
Release date - 22nd April, 2017.
- 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-infoto specify json file name, and
--dhdr10-optto enable optimization of inserting tone-map information only at IDR frames, or when the tone map information changes.
- Lambda tables for 8, 10, and 12-bit encoding revised, resulting in significant enhancement to subjective visual quality.
- Enhanced HDR10 encoding with HDR-specific QP optimzations for chroma, and luma planes of WCG content enabled; use
- 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
- Slow and veryslow presets receive a 20% speed boost at iso-quality by enabling the
- The bitrate target for x265 can now be dynamically reconfigured via the reconfigure API.
- Performance optimized SAO algorithm introduced via the
--limit-saooption; seeing 10% speed benefits at faster presets.
- x265_reconfigure API now also accepts rate-control parameters for dynamic reconfiguration.
- Several additions to data fields in x265_analysis to support
--refine-level: see x265.h for more details.
- Avoid negative offsets in x265 lambda2 table with SAO enabled.
- Fix mingw32 build error.
- Seek now enabled for pipe input, in addition to file-based input
- Fix issue of statically linking core-utils not working in linux.
- Fix visual artifacts with
- Fix bufferFill stats reported in csv.
Release date - 15th February, 2017.
- New SSIM-based RD-cost computation for improved visual quality, and efficiency; use
- 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
--multi-pass-opt-distortionto share distortion information, and
--multi-pass-opt-analysisto share other analysis information.
- A dedicated thread pool for lookahead can now be specified with
- 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.
- The number of bits used to signal the delta-QP can be optimized with the
--opt-cu-delta-qpoption; found to be useful in some scenarios for lower bitrate targets.
- Experimental feature option:–aq-motion adds new QP offsets based on relative motion of a block with respect to the movement of the frame.
- Reconfigure API now supports signalling new scaling lists.
- x265 application’s csv functionality now reports time (in milliseconds) taken to encode each frame.
--strict-cbrenables 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.
--hdrcan be used to ensure that max-cll and max-fall values are always signaled (even if 0,0).
- Fixed incorrect HW thread counting on MacOS platform.
- Fixed scaling lists support for 4:4:4 videos.
- Inconsistent output fix for
--opt-qp-pssby removing last slice’s QP from cost calculation.
- VTune profiling (enabled using ENABLE_VTUNE CMake option) now also works with 2017 VTune builds.
Release date - 26th December, 2016.
- Enhancements to TU selection algorithm with early-outs for improved speed; use
- New motion search method SEA (Successive Elimination Algorithm) supported now as :option: –me 4
- Bit-stream optimizations to improve fields in PPS and SPS for bit-rate savings through
- Enabled using VBV constraints when encoding without WPP.
- All param options dumped in SEI packet in bitstream when info selected.
- x265 now supports POWERPC-based systems. Several key functions also have optimized ALTIVEC kernels.
- Options to disable SEI and optional-VUI messages from bitstream made more descriptive.
- New option
--scenecut-biasto enable controlling bias to mark scene-cuts via cli.
- Support mono and mono16 color spaces for y4m input.
--min-cu-sizeof 64 no-longer supported for reasons of visual quality (was crashing earlier anyways.)
- API for CSV now expects version string for better integration of x265 into other applications.
Release date - 27th September, 2016
- Support for qg-size of 8
- Support for inserting non-IDR I-frames at scenecuts and when running with settings for fixed-GOP (min-keyint = max-keyint)
- Experimental support for slice-parallelism.
- Encode user-define SEI messages passed in through x265_picture object.
- Disable SEI and VUI messages from the bitstream
- Specify qpmin and qpmax
- Control number of bits to encode POC.
- QP fluctuation fix for first B-frame in mini-GOP for 2-pass encoding with tune-grain.
- Assembly fix for crashes in 32-bit from dct_sse4.
- Threadpool creation fix in windows platform.
Release date - 13th July, 2016
- uhd-bd: Enable Ultra-HD Bluray support
- 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.
- rc-grain: Enables a new ratecontrol mode specifically for grainy content. Strictly prevents QP oscillations within and between frames to avoid grain fluctuations.
- tune grain: A fully refactored and improved option to encode film grain content including QP control as well as analysis options.
- asm: ARM assembly is now enabled by default, native or cross compiled builds supported on armv6 and later systems.
API and Key Behaviour Changes¶
- x265_rc_stats added to x265_picture, containing all RC decision points for that frame
- PTL: high tier is now allowed by default, chosen only if necessary
- multi-pass: First pass now uses slow-firstpass by default, enabling better RC decisions in future passes
- pools: fix behaviour on multi-socketed Windows systems, provide more flexibility in determining thread and pool counts
- ABR: improve bits allocation in the first few frames, abr reset, vbv and cutree improved
- An SSIM calculation bug was corrected
Release date - 29th January, 2016
- Quant offsets: This feature allows block level quantization offsets to be specified for every frame. An API-only feature.
- –intra-refresh: Keyframes can be replaced by a moving column of intra blocks in non-keyframes.
- –limit-modes: Intelligently restricts mode analysis.
- –max-luma and –min-luma for luma clipping, optional for HDR use-cases
- Emergency denoising is now enabled by default in very low bitrate, VBV encodes
- x265_frame_stats returns many additional fields: maxCLL, maxFALL, residual energy, scenecut and latency logging
- –qpfile now supports frametype ‘K”
- x265 now allows CRF ratecontrol in pass N (N greater than or equal to 2)
- Chroma subsampling format YUV 4:0:0 is now fully supported and tested
Presets and Performance¶
- Recently added features lookahead-slices, limit-modes, limit-refs have been enabled by default for applicable presets.
- The default psy-rd strength has been increased to 2.0
- Multi-socket machines now use a single pool of threads that can work cross-socket.
Release date - 10th August, 2015
- Experimental support for Main12 is now enabled. Partial assembly support exists.
- 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
- limit-refs: This feature limits the references analysed for individual CUS. Provides a nice tradeoff between efficiency and performance.
- aq-mode 3: A new aq-mode that provides additional biasing for low-light conditions.
- An improved scene cut detection logic that allows ratecontrol to manage visual quality at fade-ins and fade-outs better.
Preset and Tune Options¶
- tune grain: Increases psyRdoq strength to 10.0, and rdoq-level to 2.
- qg-size: Default value changed to 32.