openh264 编码参数详细介绍

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openh264

OpenH264 是 Cisco 开源的一个 H.264 编码器，它支持 H.264 高级视频编码标准。这个编码器库适用于实时通信和流媒体应用，如 WebRTC，并且它是完全免费和开源的。OpenH264 项目在 GitHub 上进行维护，并且有一个活跃的社区，为开发者提供了丰富的文档和示例代码。

TagEncParamBase参数结构体

（SEncParamBase, *PEncParamBase）

• 说明：基础编码参数结构体
• EUsageType iUsageType
  • 编码器使用类型，参考EUsageType的定义，主要有相机实时、桌面内容、相机非实时、桌面内容非实时、输入内容所有类型一共五种类型；

/**
* @brief Encoder usage type
*/
typedef enum {CAMERA_VIDEO_REAL_TIME,      ///< camera video for real-time communicationSCREEN_CONTENT_REAL_TIME,    ///< screen content signalCAMERA_VIDEO_NON_REAL_TIME,SCREEN_CONTENT_NON_REAL_TIME,INPUT_CONTENT_TYPE_ALL,
} EUsageType;

• int iPicWidth
  • 亮度采样的图像宽，如果有多个空域层，则为最大值
• int iPicHeight
  • 亮度采样的图像高，如果有多个空域层，则为最大值
• int iTargetBitrate
  • 期望的目标比特率，单位是 bps
• RC_MODES iRCMode
  • 码率控制方式，可以参考RC_MODES中定义，主要有质量模式、码率模式、自适应质量模式、基于时间戳模式、内置 rc 模式、关闭 rc 模式。

/**
* @brief Enumerate the type of rate control mode
*/
typedef enum {RC_QUALITY_MODE = 0,     ///< quality modeRC_BITRATE_MODE = 1,     ///< bitrate modeRC_BUFFERBASED_MODE = 2, ///< no bitrate control,only using buffer status,adjust the video qualityRC_TIMESTAMP_MODE = 3, //rate control based timestampRC_BITRATE_MODE_POST_SKIP = 4, ///< this is in-building RC MODE, WILL BE DELETED after algorithm tuning!RC_OFF_MODE = -1,         ///< rate control off mode
} RC_MODES;

• float fMaxFrameRate
  • 最大输入帧率

TagEncParamExt参数结构体

（SEncParamExt）

• 说明：扩展编码参数结构体
• EUsageType iUsageType
  • 同TagEncParamBase
• int iPicWidth
  • 同TagEncParamBase
• int iPicHeight
  • 同TagEncParamBase
• int iTargetBitrate
  • 同TagEncParamBase
• RC_MODES iRCMode
  • 同TagEncParamBase
• float fMaxFrameRate
  • 同TagEncParamBase
• int iTemporalLayerNum
  • 时域分层数，最大时域层等于 4
• int iSpatialLayerNum
  • 空域分层数，取值在 1～MAX_SPATIAL_LAYER_NUM，其中MAX_SPATIAL_LAYER_NUM取值 4
• SSpatialLayerConfig sSpatialLayers[MAX_SPATIAL_LAYER_NUM]
  • 空域层配置，最大 4 层，为不同的空域层配置编码相关参数，具体可以参考SSpatialLayerConfig结构体

/**
* @brief  Structure for spatial layer configuration
*/
typedef struct {int   iVideoWidth;           ///< width of picture in luminance samples of a layerint   iVideoHeight;          ///< height of picture in luminance samples of a layerfloat fFrameRate;            ///< frame rate specified for a layerint   iSpatialBitrate;       ///< target bitrate for a spatial layer, in unit of bpsint   iMaxSpatialBitrate;    ///< maximum  bitrate for a spatial layer, in unit of bpsEProfileIdc  uiProfileIdc;   ///< value of profile IDC (PRO_UNKNOWN for auto-detection)ELevelIdc    uiLevelIdc;     ///< value of profile IDC (0 for auto-detection)int          iDLayerQp;      ///< value of level IDC (0 for auto-detection)SSliceArgument sSliceArgument;// Note: members bVideoSignalTypePresent through uiColorMatrix below are also defined in SWelsSPS in parameter_sets.h.bool      bVideoSignalTypePresent;  // false => do not write any of the following information to the headerunsigned charuiVideoFormat;        // EVideoFormatSPS; 3 bits in header; 0-5 => component, kpal, ntsc, secam, mac, undefbool      bFullRange;         // false => analog video data range [16, 235]; true => full data range [0,255]bool      bColorDescriptionPresent; // false => do not write any of the following three items to the headerunsigned charuiColorPrimaries;     // EColorPrimaries; 8 bits in header; 0 - 9 => ???, bt709, undef, ???, bt470m, bt470bg,//    smpte170m, smpte240m, film, bt2020unsigned charuiTransferCharacteristics;  // ETransferCharacteristics; 8 bits in header; 0 - 15 => ???, bt709, undef, ???, bt470m, bt470bg, smpte170m,//   smpte240m, linear, log100, log316, iec61966-2-4, bt1361e, iec61966-2-1, bt2020-10, bt2020-12unsigned charuiColorMatrix;        // EColorMatrix; 8 bits in header (corresponds to FFmpeg "colorspace"); 0 - 10 => GBR, bt709,//   undef, ???, fcc, bt470bg, smpte170m, smpte240m, YCgCo, bt2020nc, bt2020cbool bAspectRatioPresent; ///< aspect ratio present in VUIESampleAspectRatio eAspectRatio; ///< aspect ratio idcunsigned short sAspectRatioExtWidth; ///< use if aspect ratio idc == 255unsigned short sAspectRatioExtHeight; ///< use if aspect ratio idc == 255} SSpatialLayerConfig;

• ECOMPLEXITY_MODE iComplexityMode
  • 复杂度模式，用来平衡编码复杂度和编码质量，具体可参考ECOMPLEXITY_MODE 共用体，取值有LOW_COMPLEXITY、MEDIUM_COMPLEXITY、HIGH_COMPLEXITY三种模式

/**
* @brief Enumulate the complexity mode
*/
typedef enum {LOW_COMPLEXITY = 0,              ///< the lowest compleixty,the fastest speed,MEDIUM_COMPLEXITY,          ///< medium complexity, medium speed,medium qualityHIGH_COMPLEXITY             ///< high complexity, lowest speed, high quality
} ECOMPLEXITY_MODE;

• unsigned int uiIntraPeriod
  • 帧内编码帧的间隔，即 GOP 长度
• int iNumRefFrame
  • 被使用的参考帧的数量
• EParameterSetStrategy eSpsPpsIdStrategy
  • 在不同的 ID 中SPS/PPS 使用不同的策略，具体可以参考EParameterSetStrategy中定义，主要有固定 ID、每个 IDR 帧增加 ID、使用现有的 sps、使用现有 sps 同时 pps 增加、使用现有的 sps、pps。

/*** @brief Enumulate for the stategy of SPS/PPS strategy*/
typedef enum {CONSTANT_ID = 0,           ///< constant id in SPS/PPSINCREASING_ID = 0x01,      ///< SPS/PPS id increases at each IDRSPS_LISTING  = 0x02,       ///< using SPS in the existing list if possibleSPS_LISTING_AND_PPS_INCREASING  = 0x03,SPS_PPS_LISTING  = 0x06,
} EParameterSetStrategy;

• bool bPrefixNalAddingCtrl
  • false 不使用Prefix NAL，true 使用Prefix NAL
  • Prefix NAL（前缀NAL单元）是视频编码中，特别是在H.264/AVC标准里使用的一种技术。它是一种特定的NAL单元，用于在发送新的NAL单元之前提供一些额外的信息或控制指令。这种前缀可以包含重要的编码参数，比如时间戳信息、解码参数集合（如SPS和PPS）的变化信息等。
• bool bEnableSSEI
  • false 不使用 SSEI，true 使用 SSEI，todo：计划移除 SSEI 接口
• bool bSimulcastAVC
  • false 使用 svc 语法为更高层当空域层多于 1 层时，true 使用Simulcast avc
• int iPaddingFlag
  • 0 不填充，1 填充，
• int iEntropyCodingModeFlag
  • 熵编码方式，0 为 cavlc，1 为 cabac
• bool bEnableFrameSkip
  • false 无法跳帧，即使 vbv缓存溢出，true 允许跳帧保持码率在限制范围内
• int iMaxBitrate
  • 最大码率，单位是 bps，如果不需要设置为UNSPECIFIED_BIT_RATE
• int iMaxQp
  • 编码器支持的最大 qp 值
• int iMinQp
  • 编码器支持的最小 qp 值
• unsigned int uiMaxNalSize
  • 最大 NAL 大小，对于动态切片模式，该值不应该为0
• bool bEnableLongTermReference
  • 长参考开关，1 开启长参考，0 关闭长参考
• int iLTRRefNum
  • 长参考帧数量，todo：还不支持任意设置
• unsigned int iLtrMarkPeriod
  • 在反馈中标记长参考的间隔周期
• unsigned short iMultipleThreadIdc
  • 多线程设置，0 auto， 1 禁用多线程，大于 1 时计数多线程数量
• bool bUseLoadBalancing
  • 仅当uiSliceMode=1或3时使用，将在多线程编码的运行期间更改图片的切片，因此每次运行的结果可能不同
• int iLoopFilterDisableIdc
  • 去块环路滤波器，0:开启，1:关闭，2:开启，除了切片边界
• int iLoopFilterAlphaC0Offset
  • Alpha偏移量设置，取值范围[-6, 6]，默认 0
• int iLoopFilterBetaOffset
  • Beta偏移量设置，取值范围[-6, 6]，默认 0
• bool bEnableDenoise
  • 去噪控制
• bool bEnableBackgroundDetection
  • 背景检测控制
• bool bEnableAdaptiveQuant
  • 自适应量化控制
• bool bEnableFrameCroppingFlag
  • 使能帧裁剪标志:在应用中始终为TRUE
• bool bEnableSceneChangeDetect
  • 场景变化检测
• bool bIsLosslessLink
  • 长参考高级设置

编码参数默认设置

• 在 param_svc.h 文件中FillDefault (SEncParamExt& param)函数设置编码参数默认值。

static void FillDefault (SEncParamExt& param) {memset (&param, 0, sizeof (param));param.uiIntraPeriod         = 0;                    // intra period (multiple of GOP size as desired)param.iNumRefFrame          = AUTO_REF_PIC_COUNT;// number of reference frame usedparam.iPicWidth             = 0;    //   actual input picture widthparam.iPicHeight            = 0;    //   actual input picture heightparam.fMaxFrameRate         = MAX_FRAME_RATE;       // maximal frame rate [Hz / fps]param.iComplexityMode       = LOW_COMPLEXITY;param.iTargetBitrate        = UNSPECIFIED_BIT_RATE; // overall target bitrate introduced in RC moduleparam.iMaxBitrate           = UNSPECIFIED_BIT_RATE;param.iMultipleThreadIdc    = 1;param.bUseLoadBalancing = true;param.iLTRRefNum            = 0;param.iLtrMarkPeriod        = 30;   //the min distance of two int32_t referencesparam.bEnableSSEI           = false;param.bSimulcastAVC         = false;param.bEnableFrameCroppingFlag = true; // enable frame cropping flag: true alwayse in application// false: Streaming Video Sharing; true: Video Conferencing Meeting;/* Deblocking loop filter */param.iLoopFilterDisableIdc         = 0;    // 0: on, 1: off, 2: on except for slice boundariesparam.iLoopFilterAlphaC0Offset      = 0;    // AlphaOffset: valid range [-6, 6], default 0param.iLoopFilterBetaOffset         = 0;    // BetaOffset:  valid range [-6, 6], default 0/* Rate Control */param.iRCMode                       = RC_QUALITY_MODE;param.iPaddingFlag                  = 0;param.iEntropyCodingModeFlag        = 0;param.bEnableDenoise                = false;        // denoise controlparam.bEnableSceneChangeDetect      = true;         // scene change detection controlparam.bEnableBackgroundDetection    = true;         // background detection controlparam.bEnableAdaptiveQuant          = true;         // adaptive quantization controlparam.bEnableFrameSkip              = true;         // frame skippingparam.bEnableLongTermReference      = false;        // long term reference controlparam.eSpsPpsIdStrategy             = INCREASING_ID;// pSps pPps id addition controlparam.bPrefixNalAddingCtrl          = false;        // prefix NAL adding controlparam.iSpatialLayerNum              = 1;            // number of dependency(Spatial/CGS) layers used to be encodedparam.iTemporalLayerNum             = 1;            // number of temporal layer specifiedparam.iMaxQp = QP_MAX_VALUE;param.iMinQp = QP_MIN_VALUE;param.iUsageType = CAMERA_VIDEO_REAL_TIME;param.uiMaxNalSize = 0;param.bIsLosslessLink = false;for (int32_t iLayer = 0; iLayer < MAX_SPATIAL_LAYER_NUM; iLayer++) {param.sSpatialLayers[iLayer].uiProfileIdc = PRO_UNKNOWN;param.sSpatialLayers[iLayer].uiLevelIdc = LEVEL_UNKNOWN;param.sSpatialLayers[iLayer].iDLayerQp = SVC_QUALITY_BASE_QP;param.sSpatialLayers[iLayer].fFrameRate = param.fMaxFrameRate;param.sSpatialLayers[iLayer].iMaxSpatialBitrate = UNSPECIFIED_BIT_RATE;param.sSpatialLayers[iLayer].sSliceArgument.uiSliceMode = SM_SINGLE_SLICE;param.sSpatialLayers[iLayer].sSliceArgument.uiSliceNum = 0; //AUTO, using number of CPU coresparam.sSpatialLayers[iLayer].sSliceArgument.uiSliceSizeConstraint = 1500;param.sSpatialLayers[iLayer].bAspectRatioPresent = false; // do not write any of the following information to the headerparam.sSpatialLayers[iLayer].eAspectRatio = ASP_UNSPECIFIED;param.sSpatialLayers[iLayer].sAspectRatioExtWidth = 0;param.sSpatialLayers[iLayer].sAspectRatioExtHeight = 0;const int32_t kiLesserSliceNum = ((MAX_SLICES_NUM < MAX_SLICES_NUM_TMP) ? MAX_SLICES_NUM : MAX_SLICES_NUM_TMP);for (int32_t idx = 0; idx < kiLesserSliceNum; idx++)param.sSpatialLayers[iLayer].sSliceArgument.uiSliceMbNum[idx] = 0; //default, using one row a slice if uiSliceMode is SM_RASTER_MODE// See codec_app_def.h for more info about members bVideoSignalTypePresent through uiColorMatrix.  The default values// used below preserve the previous behavior; i.e., no additional information will be written to the output file.param.sSpatialLayers[iLayer].bVideoSignalTypePresent = false;     // do not write any of the following information to the headerparam.sSpatialLayers[iLayer].uiVideoFormat = VF_UNDEF;        // undefinedparam.sSpatialLayers[iLayer].bFullRange = false;            // analog video data range [16, 235]param.sSpatialLayers[iLayer].bColorDescriptionPresent = false;    // do not write any of the following three items to the headerparam.sSpatialLayers[iLayer].uiColorPrimaries = CP_UNDEF;       // undefinedparam.sSpatialLayers[iLayer].uiTransferCharacteristics = TRC_UNDEF; // undefinedparam.sSpatialLayers[iLayer].uiColorMatrix = CM_UNDEF;        // undefined}}

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