Version 2.3
Release date — 15.02.2017.
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Encoder enhancements
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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. —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
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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
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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.