forked from mirror/libbpg
183 lines
11 KiB
ReStructuredText
183 lines
11 KiB
ReStructuredText
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Preset Options
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--------------
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.. _presets:
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Presets
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=======
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x265 has a number of predefined :option:`--preset` options that make
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trade-offs between encode speed (encoded frames per second) and
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compression efficiency (quality per bit in the bitstream). The default
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preset is medium, it does a reasonably good job of finding the best
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possible quality without spending enormous CPU cycles looking for the
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absolute most efficient way to achieve that quality. As you go higher
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than medium, the encoder takes shortcuts to improve performance at the
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expense of quality and compression efficiency. As you go lower than
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medium, the encoder tries harder and harder to achieve the best quailty
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per bit compression ratio.
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The presets adjust encoder parameters to affect these trade-offs.
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| | ultrafast | superfast | veryfast | faster | fast | medium | slow | slower | veryslow | placebo |
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+==============+===========+===========+==========+========+======+========+======+========+==========+=========+
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| ctu | 32 | 32 | 32 | 64 | 64 | 64 | 64 | 64 | 64 | 64 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| min-cu-size | 16 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 | 8 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| bframes | 3 | 3 | 4 | 4 | 4 | 4 | 4 | 8 | 8 | 8 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| b-adapt | 0 | 0 | 0 | 0 | 0 | 2 | 2 | 2 | 2 | 2 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| rc-lookahead | 5 | 10 | 15 | 15 | 15 | 20 | 25 | 30 | 40 | 60 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| scenecut | 0 | 40 | 40 | 40 | 40 | 40 | 40 | 40 | 40 | 40 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| refs | 1 | 1 | 1 | 1 | 2 | 3 | 3 | 3 | 5 | 5 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| me | dia | hex | hex | hex | hex | hex | star | star | star | star |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| merange | 57 | 57 | 57 | 57 | 57 | 57 | 57 | 57 | 57 | 92 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| subme | 0 | 1 | 1 | 2 | 2 | 2 | 3 | 3 | 4 | 5 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| rect | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| amp | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| max-merge | 2 | 2 | 2 | 2 | 2 | 2 | 3 | 3 | 4 | 5 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| early-skip | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 | 0 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| fast-intra | 1 | 1 | 1 | 1 | 1 | 0 | 0 | 0 | 0 | 0 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| b-intra | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| sao | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| signhide | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| weightp | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| weightb | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| aq-mode | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| cuTree | 0 | 0 | 0 | 0 | 1 | 1 | 1 | 1 | 1 | 1 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| rdLevel | 2 | 2 | 2 | 2 | 2 | 3 | 4 | 6 | 6 | 6 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| rdoq-level | 0 | 0 | 0 | 0 | 0 | 0 | 2 | 2 | 2 | 2 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| tu-intra | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 3 | 4 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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| tu-inter | 1 | 1 | 1 | 1 | 1 | 1 | 1 | 2 | 3 | 4 |
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+--------------+-----------+-----------+----------+--------+------+--------+------+--------+----------+---------+
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Placebo mode enables transform-skip prediction evaluation.
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.. _tunings:
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Tuning
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======
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There are a few :option:`--tune` options available, which are applied
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after the preset.
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.. Note::
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The *psnr* and *ssim* tune options disable all optimizations that
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sacrafice metric scores for perceived visual quality (also known as
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psycho-visual optimizations). By default x265 always tunes for
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highest perceived visual quality but if one intends to measure an
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encode using PSNR or SSIM for the purpose of benchmarking, we highly
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recommend you configure x265 to tune for that particular metric.
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+--------------+-----------------------------------------------------+
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| --tune | effect |
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+==============+=====================================================+
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| psnr | disables adaptive quant, psy-rd, and cutree |
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+--------------+-----------------------------------------------------+
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| ssim | enables adaptive quant auto-mode, disables psy-rd |
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+--------------+-----------------------------------------------------+
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| grain | improves retention of film grain. more below |
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+--------------+-----------------------------------------------------+
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| fastdecode | no loop filters, no weighted pred, no intra in B |
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+--------------+-----------------------------------------------------+
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| zerolatency | no lookahead, no B frames, no cutree |
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+--------------+-----------------------------------------------------+
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Film Grain Retention
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~~~~~~~~~~~~~~~~~~~~
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:option:`--tune` *grain* tries to improve the retention of film grain in
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the reconstructed output. It disables rate distortion optimizations in
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quantization, and increases the default psy-rd.
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* :option:`--psy-rd` 0.5
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* :option:`--rdoq-level` 0
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* :option:`--psy-rdoq` 0
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It lowers the strength of adaptive quantization, so residual energy can
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be more evenly distributed across the (noisy) picture:
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* :option:`--aq-strength` 0.3
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And it similarly tunes rate control to prevent the slice QP from
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swinging too wildly from frame to frame:
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* :option:`--ipratio` 1.1
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* :option:`--pbratio` 1.1
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* :option:`--qcomp` 0.8
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And lastly it reduces the strength of deblocking to prevent grain being
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blurred on block boundaries:
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* :option:`--deblock` -2
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Fast Decode
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~~~~~~~~~~~
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:option:`--tune` *fastdecode* disables encoder features which tend to be
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bottlenecks for the decoder. It is intended for use with 4K content at
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high bitrates which can cause decoders to struggle. It disables both
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HEVC loop filters, which tend to be process bottlenecks:
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* :option:`--no-deblock`
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* :option:`--no-sao`
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It disables weighted prediction, which tend to be bandwidth bottlenecks:
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* :option:`--no-weightp`
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* :option:`--no-weightb`
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And it disables intra blocks in B frames with :option:`--no-b-intra`
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since intra predicted blocks cause serial dependencies in the decoder.
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Zero Latency
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~~~~~~~~~~~~
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There are two halves to the latency problem. There is latency at the
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decoder and latency at the encoder. :option:`--tune` *zerolatency*
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removes latency from both sides. The decoder latency is removed by:
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* :option:`--bframes` 0
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Encoder latency is removed by:
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* :option:`--b-adapt` 0
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* :option:`--rc-lookahead` 0
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* :option:`--no-scenecut`
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* :option:`--no-cutree`
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* :option:`--frame-threads` 1
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With all of these settings x265_encoder_encode() will run synchronously,
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the picture passed as pic_in will be encoded and returned as NALs. These
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settings disable frame parallelism, which is an important component for
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x265 performance. If you can tolerate any latency on the encoder, you
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can increase performance by increasing the number of frame threads. Each
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additional frame thread adds one frame of latency.
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