Releases

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-tuoption.
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.

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-qpoption; 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.

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 :option: –me 4
3. Bit-stream optimizations to improve fields in PPS and SPS for bit-rate savings through --opt-qp-pps, --opt-ref-list-length-pps, and --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.