x265 has support for open source HEVC encoder SVT-HEVC and can generate SVT-HEVC compliant bitstreams. SVT-HEVC encoder can be enabled at run time using --svt. Since SVT-HEVC params/CLI are not exposed outside, it has to be configured only via x265 CLI options. The API’s of SVT-HEVC are accessed through x265’s API so even library users of x265 can avail this feature, under the condition that x265_param_parse() API should be used for all param assignment. Params assigned outside of x265_param_parse() API wont’t be mapped to SVT-HEVC. This document describes the steps needed to compile x265 with SVT-HEVC and CLI options mapping between x265 and SVT-HEVC.

Supported Version

Version - 1.4.1

Build Steps

This section describes the build steps to be followed to link SVT-HEVC with x265.


  1. Clone SVT-HEVC (say at path “/home/app/”) and build it (follow the build steps in its README file)
  2. Once build is successful, binaries can be found inside the Bin folder at its root directory (“/home/app/SVT-HEVC/Bin/Release/”)


  1. Set environmental variables SVT_HEVC_INCLUDE_DIR and SVT_HEVC_LIBRARY_DIR to help x265 locate SVT-HEVC. For example:
    • export SVT_HEVC_INCLUDE_DIR = /home/app/SVT-HEVC/Source/API/
    • export SVT_HEVC_LIBRARY_DIR = /home/app/SVT-HEVC/Bin/Release/
  2. Enable the cmake option ENABLE_SVT_HEVC and continue the normal build process

CLI options Mapping

Once x265 is compiled with SVT-HEVC, SVT-HEVC encoder can be invoked at run time using --svt. --svt can be added anywhere in the command line, x265 application will automatically parse it first and maps all other x265 CLI’s present in the command line to SVT-HEVC encoder options internally and configures the same. Below table shows the actual mapping of x265 CLI options to SVT-HEVC encoder options (Name as shown in SVT-HEVC’s sample configuration file)

x265 CLI option SVT-HEVC Encoder Option Range
--input InputFile Any String
--output StreamFile Any String
--input-depth EncoderBitDepth [8, 10]
--input-res SourceWidth [64 - 8192]
SourceHeight [64 - 8192]
--frames FrameToBeEncoded Any Positive Integer
--fps FrameRateNumerator Any Positive Integer
FrameRateDenominator Any Positive Integer
--profile Profile [main, main10]
--level-idc Level
[1, 2, 2.1, 3, 3.1, 4, 4.1,
5, 5.1, 5.2, 6, 6.1, 6.2]
--high-tier Tier  
--qpmin MinQpAllowed [0 - 50]
--qpmax MaxQpAllowed [0 - 51]
--rc-lookahead LookAheadDistance [0 - 250]
--scenecut SceneChangeDetection Any Positive Integer
--open-gop IntraRefreshType  
--deblock LoopFilterDisable Any Integer
--sao SAO  
--keyint IntraPeriod [(-2) - 255]
--constrained-intra ConstrainedIntra  
--vui-timing-info VideoUsabilityInfo  
--hdr HighDynamicRangeInput  
--aud AccessUnitDelimeter  
--qp RateControlMode RateControlMode = 0
QP [0 - 51]
--bitrate RateControlMode RateControlMode = 1
TargetBitrate Any Positive Integer
--interlace InterlacedVideo [0 - 2]
--pools TargetSocket, LogicalProcessors Maximum NUMA Nodes = 2
--master-display MasteringDisplayColorVolume Any String
--max-cll maxCLL, maxFALL Any Positve Integer
--dolby-vision-profile DolbyVisionProfile [8.1]
--dolby-vision-rpu DolbyVisionRpuFile Any String
--nalu-file NaluFile Any String
--hrd hrdFlag [0, 1]
--vbv-maxrate vbvMaxrate Any Positive Integer
--vbv-bufsize vbvBufsize Any Positive Integer
--vbv-init VbvBufInit [0 - 100]
--frame-threads ThreadCount Any Number
--svt-search-width SearchAreaWidth [1 - 256]
--svt-search-height SearchAreaHeight [1 - 256]
--svt-hierarchical-level HierarchicalLevels [0 - 3]
--svt-base-layer-switch-mode BaseLayerSwitchMode [0, 1]
--svt-pred-struct PredStructure [0 - 2]
--svt-hme HME, UseDefaultMeHme  
--svt-compressed-ten-bit-format CompressedTenBitFormat  
--svt-speed-control SpeedControlFlag  
--svt-fps-in-vps FpsInVps  

x265 CLI options which are not present in the above table will have no effect if SVT-HEVC is enabled and would be ignored silently with a warning. If SVT-HEVC is enabled, accepted input range of x265 CLI options will change, because it follows SVT-HEVC encoder’s specs, which are mentioned in the Range section in the above table. Options starting with prefix “–svt-” are newly added to fecilitate access to the features of SVT-HEVC which couldn’t be mapped to the existing x265 CLI’s. So these options will have effect only if SVT-HEVC is enabled and would be ignored with default x265 encode.

Preset Option Mapping

x265 has 10 presets from ultrafast to placebo whereas SVT-HEVC has 12 presets. Use --svt-preset-tuner with Placebo preset to access the additional 2 presets of SVT-HEVC. Note that --svt-preset-tuner should be used only if SVT-HEVC is enabled and only with Placebo preset, would be ignored otherwise. Below table shows the actual mapping of presets,

x265 Preset SVT-HEVC Preset
Ultrafast 11
Superfast 10
Veryfast 9
Faster 8
Fast 7
Medium 6
Slow 5
Slower 4
Veryslow 3
Placebo 2
Placebo --svt-preset-tuner 0 0
Placebo --svt-preset-tuner 1 1