ffmpeg libx264 h264_nvenc 编码参数解析

最新推荐文章于 2025-03-06 00:08:48 发布

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EricLi404

最新推荐文章于 2025-03-06 00:08:48 发布

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分类专栏： cv ffmpeg 文章标签： cv ffmpeg nvenc x264

本文链接：https://blog.youkuaiyun.com/leiflyy/article/details/87935084

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主要AVOptions

公有AVOptions

`-preset`

主要用来调节编码速度和质量的平衡，虽然libx264和h264_nvenc都有此参数，但是该参数的可选项却不完全相同：

preset是通过设置一系列编码参数来实现调节编码速度和质量的效果的，
e.g. -preset faster 是做了如下设置 --no-mixed-refs --rc-lookahead 20 --ref 2 --subme 4 --weightp 1

详细信息见文章最后一章的x264 encoding options。

libx264 有10个选项

速度由快到慢，速度越慢，质量越好，压缩比越大；默认是medium。

ultrafast
superfast
veryfast
faster
fast
medium
slow
slower
veryslow
placebo

h264_nvenc 有11个选项

默认是medium。

slow
medium
fast
hp
hq
bd
ll
llhq
llhp
lossless
losslesshp

针对 libx264做过简单的各选项对比测试，结果如下图
在这里插入图片描述

`-profile`

用来设置画质级别，默认级别为 high：

Baseline Profile：基本画质。支持I/P 帧，只支持无交错（Progressive）和CAVLC；
Main profile：主流画质。提供I/P/B 帧，支持无交错（Progressive）和交错（Interlaced），也支持CAVLC 和CABAC 的支持；
High profile：高级画质。在main Profile 的基础上增加了8x8内部预测、自定义量化、无损视频编码和更多的YUV 格式；

H.264 Baseline profile和Main profile都是针对8位样本数据、4:2:0格式(YUV)的视频序列。在相同配置情况下，High profile（HP）可以比Main profile（MP）降低10%的码率。根据应用领域的不同，Baseline profile多应用于实时通信领域，Main profile多应用于流媒体领域，High profile则多应用于广电和存储领域。

除了这三项之外，high还衍生出了 high10、 high422、 high444、high444p 等参数。。。。。

该参数覆盖的用户设置项见文章最后一章的x264 encoding options。

`-level`

`-crf` `-cq`

crf可以根据视频的运动和静止动态的进行压缩。

与crf、cq、qp、vbr、cbr相关的解析可以参考：Understanding Rate Control Modes (x264, x265, vpx) 和 CRF Guide (Constant Rate Factor in x264 and x265)

libx264

-crf d Select the quality for constant quality mode (from -1 to FLT_MAX) (default -1)

h264_nvenc

-cq Set target quality level (0 to 51, 0 means automatic) for constant quality mode in VBR rate control (from 0 to 51) (default 0)

`-qp`

类似于crf,但相同比特率下质量更差，建议使用crf

libx264

Constant quantization parameter rate control method (from -1 to INT_MAX) (default -1)

h264_nvenc

Constant quantization parameter rate control method (from -1 to 51) (default -1)

libx264 专有参数

`-tune`

为特定类型的源或情况调整设置

主要参数有

film （电影、真人类型）
animation （动画）
grain （需要保留大量的grain时用，高比特率编码）
stillimage （静态图像编码时使用）
psnr （为提高psnr做了优化的参数）
ssim （为提高ssim做了优化的参数）
fastdecode （可以快速解码的参数）
zerolatency （零延迟，用在需要非常低的延迟的情况下，比如电视电话会议的编码）

详细 help 信息

libx264 AVOptions

查看指令ffmpeg -h encoder=libx264

ffmpeg version 4.1 Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1_1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-opencl --enable-videotoolbox
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Encoder libx264 [libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10]:
    General capabilities: delay threads
    Threading capabilities: auto
    Supported pixel formats: yuv420p yuvj420p yuv422p yuvj422p yuv444p yuvj444p nv12 nv16 nv21 yuv420p10le yuv422p10le yuv444p10le nv20le
libx264 AVOptions:
  -preset            <string>     E..V..... Set the encoding preset (cf. x264 --fullhelp) (default "medium")
  -tune              <string>     E..V..... Tune the encoding params (cf. x264 --fullhelp)
  -profile           <string>     E..V..... Set profile restrictions (cf. x264 --fullhelp)
  -fastfirstpass     <boolean>    E..V..... Use fast settings when encoding first pass (default true)
  -level             <string>     E..V..... Specify level (as defined by Annex A)
  -passlogfile       <string>     E..V..... Filename for 2 pass stats
  -wpredp            <string>     E..V..... Weighted prediction for P-frames
  -a53cc             <boolean>    E..V..... Use A53 Closed Captions (if available) (default true)
  -x264opts          <string>     E..V..... x264 options
  -crf               <float>      E..V..... Select the quality for constant quality mode (from -1 to FLT_MAX) (default -1)
  -crf_max           <float>      E..V..... In CRF mode, prevents VBV from lowering quality beyond this point. (from -1 to FLT_MAX) (default -1)
  -qp                <int>        E..V..... Constant quantization parameter rate control method (from -1 to INT_MAX) (default -1)
  -aq-mode           <int>        E..V..... AQ method (from -1 to INT_MAX) (default -1)
     none                         E..V.....
     variance                     E..V..... Variance AQ (complexity mask)
     autovariance                 E..V..... Auto-variance AQ
     autovariance-biased              E..V..... Auto-variance AQ with bias to dark scenes
  -aq-strength       <float>      E..V..... AQ strength. Reduces blocking and blurring in flat and textured areas. (from -1 to FLT_MAX) (default -1)
  -psy               <boolean>    E..V..... Use psychovisual optimizations. (default auto)
  -psy-rd            <string>     E..V..... Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.
  -rc-lookahead      <int>        E..V..... Number of frames to look ahead for frametype and ratecontrol (from -1 to INT_MAX) (default -1)
  -weightb           <boolean>    E..V..... Weighted prediction for B-frames. (default auto)
  -weightp           <int>        E..V..... Weighted prediction analysis method. (from -1 to INT_MAX) (default -1)
     none                         E..V.....
     simple                       E..V.....
     smart                        E..V.....
  -ssim              <boolean>    E..V..... Calculate and print SSIM stats. (default auto)
  -intra-refresh     <boolean>    E..V..... Use Periodic Intra Refresh instead of IDR frames. (default auto)
  -bluray-compat     <boolean>    E..V..... Bluray compatibility workarounds. (default auto)
  -b-bias            <int>        E..V..... Influences how often B-frames are used (from INT_MIN to INT_MAX) (default INT_MIN)
  -b-pyramid         <int>        E..V..... Keep some B-frames as references. (from -1 to INT_MAX) (default -1)
     none                         E..V.....
     strict                       E..V..... Strictly hierarchical pyramid
     normal                       E..V..... Non-strict (not Blu-ray compatible)
  -mixed-refs        <boolean>    E..V..... One reference per partition, as opposed to one reference per macroblock (default auto)
  -8x8dct            <boolean>    E..V..... High profile 8x8 transform. (default auto)
  -fast-pskip        <boolean>    E..V..... (default auto)
  -aud               <boolean>