背景

創(chuàng)建 x264 編碼器后，其有一組默認(rèn)的編碼器配置參數(shù)，也可以根據(jù)需要修改參數(shù)，來(lái)滿足編碼要求。

具體參數(shù)

可修改的參數(shù)，比較多，這邊只列舉一些常用的。

獲取可以配置的參數(shù)

方式1

查看 ffmpeg源碼 libx264.c，其中
static const AVOption options[] = {xx}；這表示其可修改的參數(shù)，其他編碼器類似。

static const AVOption options[] = {{ "preset",        "Set the encoding preset (cf. x264 --fullhelp)",   OFFSET(preset),        AV_OPT_TYPE_STRING, { .str = "medium" }, 0, 0, VE},{ "tune",          "Tune the encoding params (cf. x264 --fullhelp)",  OFFSET(tune),          AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},{ "profile",       "Set profile restrictions (cf. x264 --fullhelp)",  OFFSET(profile_opt),       AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},{ "fastfirstpass", "Use fast settings when encoding first pass",      OFFSET(fastfirstpass), AV_OPT_TYPE_BOOL, { .i64 = 1 }, 0, 1, VE},{"level", "Specify level (as defined by Annex A)", OFFSET(level), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},{"passlogfile", "Filename for 2 pass stats", OFFSET(stats), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},{"wpredp", "Weighted prediction for P-frames", OFFSET(wpredp), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},{"a53cc",          "Use A53 Closed Captions (if available)",          OFFSET(a53_cc),        AV_OPT_TYPE_BOOL,   {.i64 = 1}, 0, 1, VE},{"x264opts", "x264 options", OFFSET(x264opts), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, VE},{ "crf",           "Select the quality for constant quality mode",    OFFSET(crf),           AV_OPT_TYPE_FLOAT,  {.dbl = -1 }, -1, FLT_MAX, VE },{ "crf_max",       "In CRF mode, prevents VBV from lowering quality beyond this point.",OFFSET(crf_max), AV_OPT_TYPE_FLOAT, {.dbl = -1 }, -1, FLT_MAX, VE },{ "qp",            "Constant quantization parameter rate control method",OFFSET(cqp),        AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE },{ "aq-mode",       "AQ method",                                       OFFSET(aq_mode),       AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE, "aq_mode"},{ "none",          NULL,                              0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_NONE},         INT_MIN, INT_MAX, VE, "aq_mode" },{ "variance",      "Variance AQ (complexity mask)",   0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_VARIANCE},     INT_MIN, INT_MAX, VE, "aq_mode" },{ "autovariance",  "Auto-variance AQ",                0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_AUTOVARIANCE}, INT_MIN, INT_MAX, VE, "aq_mode" },
#if X264_BUILD >= 144{ "autovariance-biased", "Auto-variance AQ with bias to dark scenes", 0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_AUTOVARIANCE_BIASED}, INT_MIN, INT_MAX, VE, "aq_mode" },
#endif{ "aq-strength",   "AQ strength. Reduces blocking and blurring in flat and textured areas.", OFFSET(aq_strength), AV_OPT_TYPE_FLOAT, {.dbl = -1}, -1, FLT_MAX, VE},{ "psy",           "Use psychovisual optimizations.",                 OFFSET(psy),           AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE },{ "psy-rd",        "Strength of psychovisual optimization, in <psy-rd>:<psy-trellis> format.", OFFSET(psy_rd), AV_OPT_TYPE_STRING,  {0 }, 0, 0, VE},{ "rc-lookahead",  "Number of frames to look ahead for frametype and ratecontrol", OFFSET(rc_lookahead), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, INT_MAX, VE },{ "weightb",       "Weighted prediction for B-frames.",               OFFSET(weightb),       AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE },{ "weightp",       "Weighted prediction analysis method.",            OFFSET(weightp),       AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE, "weightp" },{ "none",          NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_NONE},   INT_MIN, INT_MAX, VE, "weightp" },{ "simple",        NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_SIMPLE}, INT_MIN, INT_MAX, VE, "weightp" },{ "smart",         NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_WEIGHTP_SMART},  INT_MIN, INT_MAX, VE, "weightp" },{ "ssim",          "Calculate and print SSIM stats.",                 OFFSET(ssim),          AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE },{ "intra-refresh", "Use Periodic Intra Refresh instead of IDR frames.",OFFSET(intra_refresh),AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE },{ "bluray-compat", "Bluray compatibility workarounds.",               OFFSET(bluray_compat) ,AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE },{ "b-bias",        "Influences how often B-frames are used",          OFFSET(b_bias),        AV_OPT_TYPE_INT,    { .i64 = INT_MIN}, INT_MIN, INT_MAX, VE },{ "b-pyramid",     "Keep some B-frames as references.",               OFFSET(b_pyramid),     AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE, "b_pyramid" },{ "none",          NULL,                                  0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_NONE},   INT_MIN, INT_MAX, VE, "b_pyramid" },{ "strict",        "Strictly hierarchical pyramid",       0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_STRICT}, INT_MIN, INT_MAX, VE, "b_pyramid" },{ "normal",        "Non-strict (not Blu-ray compatible)", 0, AV_OPT_TYPE_CONST, {.i64 = X264_B_PYRAMID_NORMAL}, INT_MIN, INT_MAX, VE, "b_pyramid" },{ "mixed-refs",    "One reference per partition, as opposed to one reference per macroblock", OFFSET(mixed_refs), AV_OPT_TYPE_BOOL, { .i64 = -1}, -1, 1, VE },{ "8x8dct",        "High profile 8x8 transform.",                     OFFSET(dct8x8),        AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE},{ "fast-pskip",    NULL,                                              OFFSET(fast_pskip),    AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE},{ "aud",           "Use access unit delimiters.",                     OFFSET(aud),           AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE},{ "mbtree",        "Use macroblock tree ratecontrol.",                OFFSET(mbtree),        AV_OPT_TYPE_BOOL,   { .i64 = -1 }, -1, 1, VE},{ "deblock",       "Loop filter parameters, in <alpha:beta> form.",   OFFSET(deblock),       AV_OPT_TYPE_STRING, { 0 },  0, 0, VE},{ "cplxblur",      "Reduce fluctuations in QP (before curve compression)", OFFSET(cplxblur), AV_OPT_TYPE_FLOAT,  {.dbl = -1 }, -1, FLT_MAX, VE},{ "partitions",    "A comma-separated list of partitions to consider. ""Possible values: p8x8, p4x4, b8x8, i8x8, i4x4, none, all", OFFSET(partitions), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},{ "direct-pred",   "Direct MV prediction mode",                       OFFSET(direct_pred),   AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE, "direct-pred" },{ "none",          NULL,      0,    AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_NONE },     0, 0, VE, "direct-pred" },{ "spatial",       NULL,      0,    AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_SPATIAL },  0, 0, VE, "direct-pred" },{ "temporal",      NULL,      0,    AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_TEMPORAL }, 0, 0, VE, "direct-pred" },{ "auto",          NULL,      0,    AV_OPT_TYPE_CONST, { .i64 = X264_DIRECT_PRED_AUTO },     0, 0, VE, "direct-pred" },{ "slice-max-size","Limit the size of each slice in bytes",           OFFSET(slice_max_size),AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE },{ "stats",         "Filename for 2 pass stats",                       OFFSET(stats),         AV_OPT_TYPE_STRING, { 0 },  0,       0, VE },{ "nal-hrd",       "Signal HRD information (requires vbv-bufsize; ""cbr not allowed in .mp4)",                        OFFSET(nal_hrd),       AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, INT_MAX, VE, "nal-hrd" },{ "none",          NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_NONE}, INT_MIN, INT_MAX, VE, "nal-hrd" },{ "vbr",           NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_VBR},  INT_MIN, INT_MAX, VE, "nal-hrd" },{ "cbr",           NULL, 0, AV_OPT_TYPE_CONST, {.i64 = X264_NAL_HRD_CBR},  INT_MIN, INT_MAX, VE, "nal-hrd" },{ "avcintra-class","AVC-Intra class 50/100/200/300/480",              OFFSET(avcintra_class),AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, 480   , VE},{ "me_method",    "Set motion estimation method",                     OFFSET(motion_est),    AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, X264_ME_TESA, VE, "motion-est"},{ "motion-est",   "Set motion estimation method",                     OFFSET(motion_est),    AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, X264_ME_TESA, VE, "motion-est"},{ "dia",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_DIA },  INT_MIN, INT_MAX, VE, "motion-est" },{ "hex",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_HEX },  INT_MIN, INT_MAX, VE, "motion-est" },{ "umh",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_UMH },  INT_MIN, INT_MAX, VE, "motion-est" },{ "esa",           NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_ESA },  INT_MIN, INT_MAX, VE, "motion-est" },{ "tesa",          NULL, 0, AV_OPT_TYPE_CONST, { .i64 = X264_ME_TESA }, INT_MIN, INT_MAX, VE, "motion-est" },{ "forced-idr",   "If forcing keyframes, force them as IDR frames.",                                  OFFSET(forced_idr),  AV_OPT_TYPE_BOOL,   { .i64 = 0 }, -1, 1, VE },{ "coder",    "Coder type",                                           OFFSET(coder), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 1, VE, "coder" },{ "default",          NULL, 0, AV_OPT_TYPE_CONST, { .i64 = -1 }, INT_MIN, INT_MAX, VE, "coder" },{ "cavlc",            NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 0 },  INT_MIN, INT_MAX, VE, "coder" },{ "cabac",            NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 1 },  INT_MIN, INT_MAX, VE, "coder" },{ "vlc",              NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 0 },  INT_MIN, INT_MAX, VE, "coder" },{ "ac",               NULL, 0, AV_OPT_TYPE_CONST, { .i64 = 1 },  INT_MIN, INT_MAX, VE, "coder" },{ "b_strategy",   "Strategy to choose between I/P/B-frames",          OFFSET(b_frame_strategy), AV_OPT_TYPE_INT, { .i64 = -1 }, -1, 2, VE },{ "chromaoffset", "QP difference between chroma and luma",            OFFSET(chroma_offset), AV_OPT_TYPE_INT, { .i64 = 0 }, INT_MIN, INT_MAX, VE },{ "sc_threshold", "Scene change threshold",                           OFFSET(scenechange_threshold), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX, VE },{ "noise_reduction", "Noise reduction",                               OFFSET(noise_reduction), AV_OPT_TYPE_INT, { .i64 = -1 }, INT_MIN, INT_MAX, VE },{ "udu_sei",      "Use user data unregistered SEI if available",      OFFSET(udu_sei),  AV_OPT_TYPE_BOOL,   { .i64 = 0 }, 0, 1, VE },{ "x264-params",  "Override the x264 configuration using a :-separated list of key=value parameters", OFFSET(x264_params), AV_OPT_TYPE_DICT, { 0 }, 0, 0, VE },{ NULL },
};

方式2

通過(guò) ffmpeg 命令行查找
ffmpeg -h encoder=libx264

常用參數(shù)講解

preset

主要調(diào)節(jié)編碼速度和質(zhì)量的平衡
可以設(shè)置的值，{ “ultrafast”, “superfast”, “veryfast”, “faster”, “fast”, “medium”, “slow”, “slower”, “veryslow”, “placebo”, 0 };
如何獲取可以設(shè)置哪些值，看注釋是編譯 x264，然后運(yùn)行 x264 --fullhelp 可以看到。我這邊嫌麻煩沒(méi)有編譯，看 x264 源碼獲取的

tune

主要配合視頻類型和視覺(jué)優(yōu)化的參數(shù)
可以設(shè)置的值，{ “film”, “animation”, “grain”, “stillimage”, “psnr”, “ssim”, “fastdecode”, “zerolatency”, 0 };
film： 電影、真人類型；
animation： 動(dòng)畫(huà)；
grain： 需要保留大量的grain時(shí)用；
psnr： 為提高psnr做了優(yōu)化的參數(shù)；
ssim： 為提高ssim做了優(yōu)化的參數(shù)；
fastdecode： 可以快速解碼的參數(shù)；
zerolatency：零延遲，用在需要非常低的延遲的情況下，比如電視電話會(huì)議的編碼。

profile

支持一組特定的編碼功能，并支持一類特定的應(yīng)用
x264_profile_names[] = { “baseline”, “main”, “high”, “high10”, “high422”, “high444”, 0 };
baseline：基本畫(huà)質(zhì)。支持I/P 幀，只支持無(wú)交錯(cuò)（Progressive）和CAVLC； 　　
main：主流畫(huà)質(zhì)。提供I/P/B 幀，支持無(wú)交錯(cuò)（Progressive）和交錯(cuò)（Interlaced），也支持CAVLC 和CABAC 的支持；
high：高級(jí)畫(huà)質(zhì)。在main Profile 的基礎(chǔ)上增加了8x8內(nèi)部預(yù)測(cè)、自定義量化、 無(wú)損視頻編碼和更多的YUV 格式；

level

每個(gè)profile 都規(guī)定了一個(gè)算法特征和限制的子集，任何遵守某個(gè)profile 的解碼器都應(yīng)該支持與其相應(yīng)的子集。
每個(gè)level都規(guī)定了一組對(duì)標(biāo)準(zhǔn)中語(yǔ)法成員（syntax element）所采用的各種參數(shù)值的限制。

nal-hrd

碼率控制方式 。
none —— 不使用 hrd
vbr —— 可變碼率
cbr —— 穩(wěn)定碼率

crf

qp

psy

rc-lookahead

參考文獻(xiàn)

https://blog.csdn.net/liuzehn/article/details/124995312
https://www.cnblogs.com/poissonnotes/p/6904728.html
https://blog.csdn.net/A199222/article/details/85785198