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.
* x265: bump to 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. --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.
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