FFmpeg与libx264接口源代码简单分析

=====================================================

H.264源代码分析文章列表：

【编码 - x264】

x264源代码简单分析：概述

x264源代码简单分析：x264命令行工具（x264.exe）

x264源代码简单分析：编码器主干部分-1

x264源代码简单分析：编码器主干部分-2

x264源代码简单分析：x264_slice_write()

x264源代码简单分析：滤波（Filter）部分

x264源代码简单分析：宏块分析（Analysis）部分-帧内宏块（Intra）

x264源代码简单分析：宏块分析（Analysis）部分-帧间宏块（Inter）

x264源代码简单分析：宏块编码（Encode）部分

x264源代码简单分析：熵编码（Entropy Encoding）部分

FFmpeg与libx264接口源代码简单分析

【解码 - libavcodec H.264 解码器】

FFmpeg的H.264解码器源代码简单分析：概述

FFmpeg的H.264解码器源代码简单分析：解析器（Parser）部分

FFmpeg的H.264解码器源代码简单分析：解码器主干部分

FFmpeg的H.264解码器源代码简单分析：熵解码（EntropyDecoding）部分

FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧内宏块（Intra）

FFmpeg的H.264解码器源代码简单分析：宏块解码（Decode）部分-帧间宏块（Inter）

FFmpeg的H.264解码器源代码简单分析：环路滤波（Loop Filter）部分

=====================================================

本文简单记录一下FFmpeg的libavcodec中与libx264接口部分的源代码。该部分源代码位于“libavcodec/libx264.c”中。正是有了这部分代码，使得FFmpeg可以调用libx264编码H.264视频。

函数调用关系图

FFmpeg的libavcodec中的libx264.c的函数调用关系如下图所示。

从图中可以看出，libx264对应的AVCodec结构体ff_libx264_encoder中设定编码器初始化函数是X264_init()，编码一帧数据的函数是X264_frame()，编码器关闭函数是X264_close()。

X264_init()调用了如下函数：

[libx264 API] x264_param_default()：设置默认参数。
[libx264 API] x264_param_default_preset()：设置默认preset。
convert_pix_fmt()：将FFmpeg像素格式转换为libx264像素格式。
[libx264 API] x264_param_apply_profile()：设置Profile。
[libx264 API] x264_encoder_open()：打开编码器。
[libx264 API] x264_encoder_headers()：需要全局头的时候，输出头信息。

X264_frame()调用了如下函数：

[libx264 API] x264_encoder_encode()：编码一帧数据。
[libx264 API] x264_encoder_delayed_frames()：输出编码器中缓存的数据。
encode_nals()：将编码后得到的x264_nal_t转换为AVPacket。

X264_close()调用了如下函数：

[libx264 API] x264_encoder_close()：关闭编码器。

下文将会分别分析X264_init()，X264_frame()和X264_close()这三个函数。

ff_libx264_encoder

ff_libx264_encoder是libx264对应的AVCodec结构体，定义如下所示。

//libx264对应的AVCodec结构体
AVCodec ff_libx264_encoder = {.name             = "libx264",.long_name        = NULL_IF_CONFIG_SMALL("libx264 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10"),.type             = AVMEDIA_TYPE_VIDEO,.id               = AV_CODEC_ID_H264,.priv_data_size   = sizeof(X264Context),.init             = X264_init,.encode2          = X264_frame,.close            = X264_close,.capabilities     = CODEC_CAP_DELAY | CODEC_CAP_AUTO_THREADS,.priv_class       = &x264_class,.defaults         = x264_defaults,.init_static_data = X264_init_static,
};

从ff_libx264_encoder定义中可以看出：init()指向X264_init()，encode2()指向 X264_frame()， close()指向 X264_close()。此外priv_class指向一个x264_class静态结构体，该结构体是libx264对应的AVClass，定义如下。

static const AVClass x264_class = {.class_name = "libx264",.item_name  = av_default_item_name,.option     = options,//选项.version    = LIBAVUTIL_VERSION_INT,
};

x264_class中的option指向一个options[]静态数组，其中包含了libx264支持的AVOption选项，如下所示。

//FFmpeg针对libx264提供的可以通过AVOption设置的选项
#define OFFSET(x) offsetof(X264Context, x)
#define VE AV_OPT_FLAG_VIDEO_PARAM | AV_OPT_FLAG_ENCODING_PARAM
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),       AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE},{ "fastfirstpass", "Use fast settings when encoding first pass",      OFFSET(fastfirstpass), AV_OPT_TYPE_INT,    { .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},{"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 (experimental)", 0, AV_OPT_TYPE_CONST, {.i64 = X264_AQ_AUTOVARIANCE}, INT_MIN, INT_MAX, VE, "aq_mode" },{ "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_INT,    { .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_INT,    { .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_INT,    { .i64 = -1 }, -1, 1, VE },{ "intra-refresh", "Use Periodic Intra Refresh instead of IDR frames.",OFFSET(intra_refresh),AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, 1, VE },{ "bluray-compat", "Bluray compatibility workarounds.",               OFFSET(bluray_compat) ,AV_OPT_TYPE_INT,    { .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_INT, { .i64 = -1}, -1, 1, VE },{ "8x8dct",        "High profile 8x8 transform.",                     OFFSET(dct8x8),        AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, 1, VE},{ "fast-pskip",    NULL,                                              OFFSET(fast_pskip),    AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, 1, VE},{ "aud",           "Use access unit delimiters.",                     OFFSET(aud),           AV_OPT_TYPE_INT,    { .i64 = -1 }, -1, 1, VE},{ "mbtree",        "Use macroblock tree ratecontrol.",                OFFSET(mbtree),        AV_OPT_TYPE_INT,    { .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",                      OFFSET(avcintra_class),AV_OPT_TYPE_INT,     { .i64 = -1 }, -1, 200   , VE},{ "x264-params",  "Override the x264 configuration using a :-separated list of key=value parameters", OFFSET(x264_params), AV_OPT_TYPE_STRING, { 0 }, 0, 0, VE },{ NULL },
};

options[]数组中包含的选项支持在FFmpeg中通过AVOption进行设置。

X264_init()

X264_init()用于初始化libx264编码器。该函数的定义如下所示。

//libx264编码器初始化
static av_cold int X264_init(AVCodecContext *avctx)
{//FFmpeg中针对libx264的私有结构体X264Context *x4 = avctx->priv_data;int sw,sh;if (avctx->global_quality > 0)av_log(avctx, AV_LOG_WARNING, "-qscale is ignored, -crf is recommended.\n");//[libx264 API] 设置默认参数x264_param_default(&x4->params);x4->params.b_deblocking_filter         = avctx->flags & CODEC_FLAG_LOOP_FILTER;if (x4->preset || x4->tune)if (x264_param_default_preset(&x4->params, x4->preset, x4->tune) < 0) {  //[libx264 API] 设置presetint i;av_log(avctx, AV_LOG_ERROR, "Error setting preset/tune %s/%s.\n", x4->preset, x4->tune);av_log(avctx, AV_LOG_INFO, "Possible presets:");for (i = 0; x264_preset_names[i]; i++)av_log(avctx, AV_LOG_INFO, " %s", x264_preset_names[i]);av_log(avctx, AV_LOG_INFO, "\n");av_log(avctx, AV_LOG_INFO, "Possible tunes:");for (i = 0; x264_tune_names[i]; i++)av_log(avctx, AV_LOG_INFO, " %s", x264_tune_names[i]);av_log(avctx, AV_LOG_INFO, "\n");return AVERROR(EINVAL);}if (avctx->level > 0)x4->params.i_level_idc = avctx->level;//libx264日志输出设置为FFmpeg的日志输出x4->params.pf_log               = X264_log;x4->params.p_log_private        = avctx;x4->params.i_log_level          = X264_LOG_DEBUG;//FFmpeg像素格式映射到libx264x4->params.i_csp                = convert_pix_fmt(avctx->pix_fmt);OPT_STR("weightp", x4->wpredp);//FFmpeg码率映射到libx264if (avctx->bit_rate) {x4->params.rc.i_bitrate   = avctx->bit_rate / 1000;x4->params.rc.i_rc_method = X264_RC_ABR;}x4->params.rc.i_vbv_buffer_size = avctx->rc_buffer_size / 1000;x4->params.rc.i_vbv_max_bitrate = avctx->rc_max_rate    / 1000;x4->params.rc.b_stat_write      = avctx->flags & CODEC_FLAG_PASS1;if (avctx->flags & CODEC_FLAG_PASS2) {x4->params.rc.b_stat_read = 1;} else {if (x4->crf >= 0) {x4->params.rc.i_rc_method   = X264_RC_CRF;x4->params.rc.f_rf_constant = x4->crf;} else if (x4->cqp >= 0) {x4->params.rc.i_rc_method   = X264_RC_CQP;x4->params.rc.i_qp_constant = x4->cqp;}if (x4->crf_max >= 0)x4->params.rc.f_rf_constant_max = x4->crf_max;}if (avctx->rc_buffer_size && avctx->rc_initial_buffer_occupancy > 0 &&(avctx->rc_initial_buffer_occupancy <= avctx->rc_buffer_size)) {x4->params.rc.f_vbv_buffer_init =(float)avctx->rc_initial_buffer_occupancy / avctx->rc_buffer_size;}OPT_STR("level", x4->level);if (avctx->i_quant_factor > 0)x4->params.rc.f_ip_factor         = 1 / fabs(avctx->i_quant_factor);if (avctx->b_quant_factor > 0)x4->params.rc.f_pb_factor         = avctx->b_quant_factor;if (avctx->chromaoffset)x4->params.analyse.i_chroma_qp_offset = avctx->chromaoffset;//FFmpeg运动估计方法映射到libx264if (avctx->me_method == ME_EPZS)x4->params.analyse.i_me_method = X264_ME_DIA;else if (avctx->me_method == ME_HEX)x4->params.analyse.i_me_method = X264_ME_HEX;else if (avctx->me_method == ME_UMH)x4->params.analyse.i_me_method = X264_ME_UMH;else if (avctx->me_method == ME_FULL)x4->params.analyse.i_me_method = X264_ME_ESA;else if (avctx->me_method == ME_TESA)x4->params.analyse.i_me_method = X264_ME_TESA;//把AVCodecContext的值（主要是编码时候的一些通用选项）映射到x264_param_tif (avctx->gop_size >= 0)x4->params.i_keyint_max         = avctx->gop_size;if (avctx->max_b_frames >= 0)x4->params.i_bframe             = avctx->max_b_frames;if (avctx->scenechange_threshold >= 0)x4->params.i_scenecut_threshold = avctx->scenechange_threshold;if (avctx->qmin >= 0)x4->params.rc.i_qp_min          = avctx->qmin;if (avctx->qmax >= 0)x4->params.rc.i_qp_max          = avctx->qmax;if (avctx->max_qdiff >= 0)x4->params.rc.i_qp_step         = avctx->max_qdiff;if (avctx->qblur >= 0)x4->params.rc.f_qblur           = avctx->qblur;     /* temporally blur quants */if (avctx->qcompress >= 0)x4->params.rc.f_qcompress       = avctx->qcompress; /* 0.0 => cbr, 1.0 => constant qp */if (avctx->refs >= 0)x4->params.i_frame_reference    = avctx->refs;else if (x4->level) {int i;int mbn = FF_CEIL_RSHIFT(avctx->width, 4) * FF_CEIL_RSHIFT(avctx->height, 4);int level_id = -1;char *tail;int scale = X264_BUILD < 129 ? 384 : 1;if (!strcmp(x4->level, "1b")) {level_id = 9;} else if (strlen(x4->level) <= 3){level_id = av_strtod(x4->level, &tail) * 10 + 0.5;if (*tail)level_id = -1;}if (level_id <= 0)av_log(avctx, AV_LOG_WARNING, "Failed to parse level\n");for (i = 0; i<x264_levels[i].level_idc; i++)if (x264_levels[i].level_idc == level_id)x4->params.i_frame_reference = av_clip(x264_levels[i].dpb / mbn / scale, 1, x4->params.i_frame_reference);}if (avctx->trellis >= 0)x4->params.analyse.i_trellis    = avctx->trellis;if (avctx->me_range >= 0)x4->params.analyse.i_me_range   = avctx->me_range;if (avctx->noise_reduction >= 0)x4->params.analyse.i_noise_reduction = avctx->noise_reduction;if (avctx->me_subpel_quality >= 0)x4->params.analyse.i_subpel_refine   = avctx->me_subpel_quality;if (avctx->b_frame_strategy >= 0)x4->params.i_bframe_adaptive = avctx->b_frame_strategy;if (avctx->keyint_min >= 0)x4->params.i_keyint_min = avctx->keyint_min;if (avctx->coder_type >= 0)x4->params.b_cabac = avctx->coder_type == FF_CODER_TYPE_AC;if (avctx->me_cmp >= 0)x4->params.analyse.b_chroma_me = avctx->me_cmp & FF_CMP_CHROMA;//把X264Context中的信息（主要是针对于libx264的一些选项）映射到x264_param_tif (x4->aq_mode >= 0)x4->params.rc.i_aq_mode = x4->aq_mode;if (x4->aq_strength >= 0)x4->params.rc.f_aq_strength = x4->aq_strength;PARSE_X264_OPT("psy-rd", psy_rd);PARSE_X264_OPT("deblock", deblock);PARSE_X264_OPT("partitions", partitions);PARSE_X264_OPT("stats", stats);if (x4->psy >= 0)x4->params.analyse.b_psy  = x4->psy;if (x4->rc_lookahead >= 0)x4->params.rc.i_lookahead = x4->rc_lookahead;if (x4->weightp >= 0)x4->params.analyse.i_weighted_pred = x4->weightp;if (x4->weightb >= 0)x4->params.analyse.b_weighted_bipred = x4->weightb;if (x4->cplxblur >= 0)x4->params.rc.f_complexity_blur = x4->cplxblur;if (x4->ssim >= 0)x4->params.analyse.b_ssim = x4->ssim;if (x4->intra_refresh >= 0)x4->params.b_intra_refresh = x4->intra_refresh;if (x4->bluray_compat >= 0) {x4->params.b_bluray_compat = x4->bluray_compat;x4->params.b_vfr_input = 0;}if (x4->avcintra_class >= 0)
#if X264_BUILD >= 142x4->params.i_avcintra_class = x4->avcintra_class;
#elseav_log(avctx, AV_LOG_ERROR,"x264 too old for AVC Intra, at least version 142 needed\n");
#endifif (x4->b_bias != INT_MIN)x4->params.i_bframe_bias              = x4->b_bias;if (x4->b_pyramid >= 0)x4->params.i_bframe_pyramid = x4->b_pyramid;if (x4->mixed_refs >= 0)x4->params.analyse.b_mixed_references = x4->mixed_refs;if (x4->dct8x8 >= 0)x4->params.analyse.b_transform_8x8    = x4->dct8x8;if (x4->fast_pskip >= 0)x4->params.analyse.b_fast_pskip       = x4->fast_pskip;if (x4->aud >= 0)x4->params.b_aud                      = x4->aud;if (x4->mbtree >= 0)x4->params.rc.b_mb_tree               = x4->mbtree;if (x4->direct_pred >= 0)x4->params.analyse.i_direct_mv_pred   = x4->direct_pred;if (x4->slice_max_size >= 0)x4->params.i_slice_max_size =  x4->slice_max_size;else {/** Allow x264 to be instructed through AVCodecContext about the maximum* size of the RTP payload. For example, this enables the production of* payload suitable for the H.264 RTP packetization-mode 0 i.e. single* NAL unit per RTP packet.*/if (avctx->rtp_payload_size)x4->params.i_slice_max_size = avctx->rtp_payload_size;}if (x4->fastfirstpass)x264_param_apply_fastfirstpass(&x4->params);/* Allow specifying the x264 profile through AVCodecContext. *///设置Profileif (!x4->profile)switch (avctx->profile) {case FF_PROFILE_H264_BASELINE:x4->profile = av_strdup("baseline");break;case FF_PROFILE_H264_HIGH:x4->profile = av_strdup("high");break;case FF_PROFILE_H264_HIGH_10:x4->profile = av_strdup("high10");break;case FF_PROFILE_H264_HIGH_422:x4->profile = av_strdup("high422");break;case FF_PROFILE_H264_HIGH_444:x4->profile = av_strdup("high444");break;case FF_PROFILE_H264_MAIN:x4->profile = av_strdup("main");break;default:break;}if (x4->nal_hrd >= 0)x4->params.i_nal_hrd = x4->nal_hrd;//if (x4->profile)if (x264_param_apply_profile(&x4->params, x4->profile) < 0) {int i;av_log(avctx, AV_LOG_ERROR, "Error setting profile %s.\n", x4->profile);av_log(avctx, AV_LOG_INFO, "Possible profiles:");for (i = 0; x264_profile_names[i]; i++)av_log(avctx, AV_LOG_INFO, " %s", x264_profile_names[i]);av_log(avctx, AV_LOG_INFO, "\n");return AVERROR(EINVAL);}//宽高，帧率等x4->params.i_width          = avctx->width;x4->params.i_height         = avctx->height;av_reduce(&sw, &sh, avctx->sample_aspect_ratio.num, avctx->sample_aspect_ratio.den, 4096);x4->params.vui.i_sar_width  = sw;x4->params.vui.i_sar_height = sh;x4->params.i_timebase_den = avctx->time_base.den;x4->params.i_timebase_num = avctx->time_base.num;x4->params.i_fps_num = avctx->time_base.den;x4->params.i_fps_den = avctx->time_base.num * avctx->ticks_per_frame;x4->params.analyse.b_psnr = avctx->flags & CODEC_FLAG_PSNR;x4->params.i_threads      = avctx->thread_count;if (avctx->thread_type)x4->params.b_sliced_threads = avctx->thread_type == FF_THREAD_SLICE;x4->params.b_interlaced   = avctx->flags & CODEC_FLAG_INTERLACED_DCT;x4->params.b_open_gop     = !(avctx->flags & CODEC_FLAG_CLOSED_GOP);x4->params.i_slice_count  = avctx->slices;x4->params.vui.b_fullrange = avctx->pix_fmt == AV_PIX_FMT_YUVJ420P ||avctx->pix_fmt == AV_PIX_FMT_YUVJ422P ||avctx->pix_fmt == AV_PIX_FMT_YUVJ444P ||avctx->color_range == AVCOL_RANGE_JPEG;if (avctx->colorspace != AVCOL_SPC_UNSPECIFIED)x4->params.vui.i_colmatrix = avctx->colorspace;if (avctx->color_primaries != AVCOL_PRI_UNSPECIFIED)x4->params.vui.i_colorprim = avctx->color_primaries;if (avctx->color_trc != AVCOL_TRC_UNSPECIFIED)x4->params.vui.i_transfer  = avctx->color_trc;if (avctx->flags & CODEC_FLAG_GLOBAL_HEADER)x4->params.b_repeat_headers = 0;if(x4->x264opts){const char *p= x4->x264opts;while(p){char param[256]={0}, val[256]={0};if(sscanf(p, "%255[^:=]=%255[^:]", param, val) == 1){OPT_STR(param, "1");}elseOPT_STR(param, val);p= strchr(p, ':');p+=!!p;}}if (x4->x264_params) {AVDictionary *dict    = NULL;AVDictionaryEntry *en = NULL;if (!av_dict_parse_string(&dict, x4->x264_params, "=", ":", 0)) {while ((en = av_dict_get(dict, "", en, AV_DICT_IGNORE_SUFFIX))) {if (x264_param_parse(&x4->params, en->key, en->value) < 0)av_log(avctx, AV_LOG_WARNING,"Error parsing option '%s = %s'.\n",en->key, en->value);}av_dict_free(&dict);}}// update AVCodecContext with x264 parametersavctx->has_b_frames = x4->params.i_bframe ?x4->params.i_bframe_pyramid ? 2 : 1 : 0;if (avctx->max_b_frames < 0)avctx->max_b_frames = 0;avctx->bit_rate = x4->params.rc.i_bitrate*1000;//-------------------------//设置完参数后，打开编码器x4->enc = x264_encoder_open(&x4->params);if (!x4->enc)return -1;avctx->coded_frame = av_frame_alloc();if (!avctx->coded_frame)return AVERROR(ENOMEM);//如果需要全局头if (avctx->flags & CODEC_FLAG_GLOBAL_HEADER) {x264_nal_t *nal;uint8_t *p;int nnal, s, i;s = x264_encoder_headers(x4->enc, &nal, &nnal);avctx->extradata = p = av_malloc(s);for (i = 0; i < nnal; i++) {/* Don't put the SEI in extradata. */if (nal[i].i_type == NAL_SEI) {av_log(avctx, AV_LOG_INFO, "%s\n", nal[i].p_payload+25);x4->sei_size = nal[i].i_payload;x4->sei      = av_malloc(x4->sei_size);memcpy(x4->sei, nal[i].p_payload, nal[i].i_payload);continue;}memcpy(p, nal[i].p_payload, nal[i].i_payload);p += nal[i].i_payload;}avctx->extradata_size = p - avctx->extradata;}return 0;
}

从源代码可以看出，X264_init()主要将各种选项值传递给libx264。这些选项有两个来源：AVCodecContext和X264Context。AVCodecContext中包含了编码器的一些通用选项，而X264Context包含了一些libx264特有的选项。在这里需要注意，FFmpeg中的一些选项的单位和libx264中对应选项的单位是不一样的，因此需要做一些转换。例如像素格式的转换函数convert_pix_fmt()就是完成了这个功能。该函数的定义如下所示。

//映射FFmpeg和libx264的像素格式
static int convert_pix_fmt(enum AVPixelFormat pix_fmt)
{switch (pix_fmt) {case AV_PIX_FMT_YUV420P:case AV_PIX_FMT_YUVJ420P:case AV_PIX_FMT_YUV420P9:case AV_PIX_FMT_YUV420P10: return X264_CSP_I420;case AV_PIX_FMT_YUV422P:case AV_PIX_FMT_YUVJ422P:case AV_PIX_FMT_YUV422P10: return X264_CSP_I422;case AV_PIX_FMT_YUV444P:case AV_PIX_FMT_YUVJ444P:case AV_PIX_FMT_YUV444P9:case AV_PIX_FMT_YUV444P10: return X264_CSP_I444;
#ifdef X264_CSP_BGRcase AV_PIX_FMT_BGR24:return X264_CSP_BGR;case AV_PIX_FMT_RGB24:return X264_CSP_RGB;
#endifcase AV_PIX_FMT_NV12:      return X264_CSP_NV12;case AV_PIX_FMT_NV16:case AV_PIX_FMT_NV20:      return X264_CSP_NV16;};return 0;
}

可以看出convert_pix_fmt()将AV_PIX_FMT_XXX转换成了X264_CSP_XXX。
在一切参数设置完毕后，X264_init()会调用x264_encoder_open()打开编码器，完成初始化工作。

X264_frame()

X264_frame()用于编码一帧视频数据。该函数的定义如下所示。

//libx264编码1帧数据
//
// AVFrame --> x264_picture_t --> x264_nal_t --> AVPacket
//
static int X264_frame(AVCodecContext *ctx, AVPacket *pkt, const AVFrame *frame,int *got_packet)
{X264Context *x4 = ctx->priv_data;x264_nal_t *nal;int nnal, i, ret;x264_picture_t pic_out = {0};AVFrameSideData *side_data;x264_picture_init( &x4->pic );x4->pic.img.i_csp   = x4->params.i_csp;if (x264_bit_depth > 8)x4->pic.img.i_csp |= X264_CSP_HIGH_DEPTH;x4->pic.img.i_plane = avfmt2_num_planes(ctx->pix_fmt);if (frame) {//将AVFrame中的数据赋值给x264_picture_t//// AVFrame --> x264_picture_t//for (i = 0; i < x4->pic.img.i_plane; i++) {x4->pic.img.plane[i]    = frame->data[i];x4->pic.img.i_stride[i] = frame->linesize[i];}x4->pic.i_pts  = frame->pts;//设置帧类型x4->pic.i_type =frame->pict_type == AV_PICTURE_TYPE_I ? X264_TYPE_KEYFRAME :frame->pict_type == AV_PICTURE_TYPE_P ? X264_TYPE_P :frame->pict_type == AV_PICTURE_TYPE_B ? X264_TYPE_B :X264_TYPE_AUTO;//检查参数设置是否正确，不正确就重新设置if (x4->avcintra_class < 0) {if (x4->params.b_interlaced && x4->params.b_tff != frame->top_field_first) {x4->params.b_tff = frame->top_field_first;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->params.vui.i_sar_height != ctx->sample_aspect_ratio.den ||x4->params.vui.i_sar_width  != ctx->sample_aspect_ratio.num) {x4->params.vui.i_sar_height = ctx->sample_aspect_ratio.den;x4->params.vui.i_sar_width  = ctx->sample_aspect_ratio.num;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->params.rc.i_vbv_buffer_size != ctx->rc_buffer_size / 1000 ||x4->params.rc.i_vbv_max_bitrate != ctx->rc_max_rate    / 1000) {x4->params.rc.i_vbv_buffer_size = ctx->rc_buffer_size / 1000;x4->params.rc.i_vbv_max_bitrate = ctx->rc_max_rate    / 1000;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->params.rc.i_rc_method == X264_RC_ABR &&x4->params.rc.i_bitrate != ctx->bit_rate / 1000) {x4->params.rc.i_bitrate = ctx->bit_rate / 1000;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->crf >= 0 &&x4->params.rc.i_rc_method == X264_RC_CRF &&x4->params.rc.f_rf_constant != x4->crf) {x4->params.rc.f_rf_constant = x4->crf;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->params.rc.i_rc_method == X264_RC_CQP &&x4->cqp >= 0 &&x4->params.rc.i_qp_constant != x4->cqp) {x4->params.rc.i_qp_constant = x4->cqp;x264_encoder_reconfig(x4->enc, &x4->params);}if (x4->crf_max >= 0 &&x4->params.rc.f_rf_constant_max != x4->crf_max) {x4->params.rc.f_rf_constant_max = x4->crf_max;x264_encoder_reconfig(x4->enc, &x4->params);}}side_data = av_frame_get_side_data(frame, AV_FRAME_DATA_STEREO3D);if (side_data) {AVStereo3D *stereo = (AVStereo3D *)side_data->data;int fpa_type;switch (stereo->type) {case AV_STEREO3D_CHECKERBOARD:fpa_type = 0;break;case AV_STEREO3D_COLUMNS:fpa_type = 1;break;case AV_STEREO3D_LINES:fpa_type = 2;break;case AV_STEREO3D_SIDEBYSIDE:fpa_type = 3;break;case AV_STEREO3D_TOPBOTTOM:fpa_type = 4;break;case AV_STEREO3D_FRAMESEQUENCE:fpa_type = 5;break;default:fpa_type = -1;break;}if (fpa_type != x4->params.i_frame_packing) {x4->params.i_frame_packing = fpa_type;x264_encoder_reconfig(x4->enc, &x4->params);}}}do {//[libx264 API] 编码//// x264_picture_t --> x264_nal_t//if (x264_encoder_encode(x4->enc, &nal, &nnal, frame? &x4->pic: NULL, &pic_out) < 0)return -1;//把x264_nal_t赋值给AVPacket//// x264_nal_t --> AVPacket//ret = encode_nals(ctx, pkt, nal, nnal);if (ret < 0)return -1;} while (!ret && !frame && x264_encoder_delayed_frames(x4->enc));//赋值AVPacket相关的字段pkt->pts = pic_out.i_pts;pkt->dts = pic_out.i_dts;switch (pic_out.i_type) {case X264_TYPE_IDR:case X264_TYPE_I:ctx->coded_frame->pict_type = AV_PICTURE_TYPE_I;break;case X264_TYPE_P:ctx->coded_frame->pict_type = AV_PICTURE_TYPE_P;break;case X264_TYPE_B:case X264_TYPE_BREF:ctx->coded_frame->pict_type = AV_PICTURE_TYPE_B;break;}pkt->flags |= AV_PKT_FLAG_KEY*pic_out.b_keyframe;if (ret)ctx->coded_frame->quality = (pic_out.i_qpplus1 - 1) * FF_QP2LAMBDA;*got_packet = ret;return 0;
}

从源代码可以看出，X264_frame()调用x264_encoder_encode()完成了编码工作。x264_encoder_encode()的输入是x264_picture_t，输出是x264_nal_t；而X264_frame()的输入是AVFrame，输出是AVPacket。因此X264_frame()在调用编码函数前将AVFrame转换成了x264_picture_t，而在调用编码函数之后调用encode_nals()将x264_nal_t转换成了AVPacket。转换函数encode_nals()的定义如下所示。

//把x264_nal_t赋值给AVPacket
//
// x264_nal_t --> AVPacket
//
static int encode_nals(AVCodecContext *ctx, AVPacket *pkt,const x264_nal_t *nals, int nnal)
{X264Context *x4 = ctx->priv_data;uint8_t *p;int i, size = x4->sei_size, ret;if (!nnal)return 0;//NALU的大小//可能有多个NALUfor (i = 0; i < nnal; i++)size += nals[i].i_payload;if ((ret = ff_alloc_packet2(ctx, pkt, size)) < 0)return ret;//p指向AVPacket的datap = pkt->data;/* Write the SEI as part of the first frame. */if (x4->sei_size > 0 && nnal > 0) {if (x4->sei_size > size) {av_log(ctx, AV_LOG_ERROR, "Error: nal buffer is too small\n");return -1;}memcpy(p, x4->sei, x4->sei_size);p += x4->sei_size;x4->sei_size = 0;av_freep(&x4->sei);}//拷贝x264_nal_t的数据至AVPacket的数据//可能有多个NALUfor (i = 0; i < nnal; i++){memcpy(p, nals[i].p_payload, nals[i].i_payload);p += nals[i].i_payload;}return 1;
}

从源代码可以看出，encode_nals()的作用就是将多个x264_nal_t合并为一个AVPacket。

X264_close()

X264_close()用于关闭libx264解码器。该函数的定义如下所示。

//libx264关闭解码器
static av_cold int X264_close(AVCodecContext *avctx)
{X264Context *x4 = avctx->priv_data;av_freep(&avctx->extradata);av_freep(&x4->sei);//[libx264 API] 关闭解码器if (x4->enc)x264_encoder_close(x4->enc);av_frame_free(&avctx->coded_frame);return 0;
}

可以看出X264_close()调用x264_encoder_close()关闭了libx264编码器。

雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020