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HEVC源码分析文章列表：
【解码 -libavcodec HEVC 解码器】
FFmpeg的HEVC解码器源码简单分析：概述
FFmpeg的HEVC解码器源码简单分析：解析器（Parser）部分
FFmpeg的HEVC解码器源码简单分析：解码器主干部分
FFmpeg的HEVC解码器源码简单分析：CTU解码（CTU Decode）部分-PU
FFmpeg的HEVC解码器源码简单分析：CTU解码（CTU Decode）部分-TU
FFmpeg的HEVC解码器源码简单分析：环路滤波（LoopFilter）
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本文分析FFmpeg的libavcodec中的HEVC解码器的主干部分。“主干部分”是相对于“CTU解码”、 “环路滤波”这些细节部分而言的。它包括了HEVC解码器直到hls_decode_entry()前面的函数调用关系（hls_decode_entry()后面就是HEVC解码器的细节部分，主要包括了“CTU解码”、 “环路滤波”2个部分）。
函数调用关系图
FFmpeg HEVC解码器主干部分在整个HEVC解码器中的位置例如以下图所看到的。
单击查看更清晰的大图
HEVC解码器主干部分的源码的调用关系例如以下图所看到的。
单击查看更清晰的大图
从图中能够看出，HEVC解码器初始化函数是hevc_decode_init()，解码函数是hevc_decode_frame()，关闭函数是hevc_decode_free()。当中hevc_decode_frame()调用了decode_nal_units()进行一帧NALU的解码，decode_nal_units()又调用了decode_nal_unit()进行一个NALU的解码。
decode_nal_unit()一方面调用解析函数ff_hevc_decode_nal_vps()，ff_hevc_decode_nal_sps()，ff_hevc_decode_nal_pps()等对VPS、SPS、PPS进行解析；还有一方面调用了hls_slice_header()和hls_slice_data()对Slice数据进行解码。
hls_slice_data()中调用了hls_decode_entry()。在当中完毕了Slice Data解码的流程。该流程包括了CU、PU、TU解码，环路滤波、SAO滤波等环节。
ff_hevc_decoder
ff_hevc_decoder是HEVC解码器相应的AVCodec结构体。该结构体的定义位于libavcodec\hevc.c，例如以下所看到的。AVCodec ff_hevc_decoder = {.name = "hevc",.long_name = NULL_IF_CONFIG_SMALL("HEVC (High Efficiency Video Coding)"),.type = AVMEDIA_TYPE_VIDEO,.id = AV_CODEC_ID_HEVC,.priv_data_size = sizeof(HEVCContext),.priv_class = &hevc_decoder_class,.init = hevc_decode_init,.close = hevc_decode_free,.decode = hevc_decode_frame,.flush = hevc_decode_flush,.update_thread_context = hevc_update_thread_context,.init_thread_copy = hevc_init_thread_copy,.capabilities = CODEC_CAP_DR1 | CODEC_CAP_DELAY |CODEC_CAP_SLICE_THREADS | CODEC_CAP_FRAME_THREADS,.profiles = NULL_IF_CONFIG_SMALL(profiles),
};hevc_decode_init()
hevc_decode_init()用于初始化HEVC解码器。该函数的定义例如以下。
//初始化HEVC解码器
static av_cold int hevc_decode_init(AVCodecContext *avctx)
{HEVCContext *s = avctx->priv_data;int ret;//初始化CABACff_init_cabac_states();avctx->internal->allocate_progress = 1;//为HEVCContext中的变量分配内存空间ret = hevc_init_context(avctx);if (ret < 0)return ret;s->enable_parallel_tiles = 0;s->picture_struct = 0;if(avctx->active_thread_type & FF_THREAD_SLICE)s->threads_number = avctx->thread_count;elses->threads_number = 1;//假设AVCodecContext中包括extradata。则解码之if (avctx->extradata_size > 0 && avctx->extradata) {ret = hevc_decode_extradata(s);if (ret < 0) {hevc_decode_free(avctx);return ret;}}if((avctx->active_thread_type & FF_THREAD_FRAME) && avctx->thread_count > 1)s->threads_type = FF_THREAD_FRAME;elses->threads_type = FF_THREAD_SLICE;return 0;
}
从源码中能够看出，hevc_decode_init()对HEVCContext中的变量做了一些初始化工作。当中调用了一个函数hevc_init_context()用于给HEVCContext中的变量分配内存空间。
hevc_init_context()
hevc_init_context()用于给HEVCContext中的变量分配内存空间。该函数的定义例如以下所看到的。//为HEVCContext中的变量分配内存空间
static av_cold int hevc_init_context(AVCodecContext *avctx)
{HEVCContext *s = avctx->priv_data;int i;s->avctx = avctx;s->HEVClc = av_mallocz(sizeof(HEVCLocalContext));if (!s->HEVClc)goto fail;s->HEVClcList[0] = s->HEVClc;s->sList[0] = s;s->cabac_state = av_malloc(HEVC_CONTEXTS);if (!s->cabac_state)goto fail;s->tmp_frame = av_frame_alloc();if (!s->tmp_frame)goto fail;s->output_frame = av_frame_alloc();if (!s->output_frame)goto fail;for (i = 0; i < FF_ARRAY_ELEMS(s->DPB); i++) {s->DPB[i].frame = av_frame_alloc();if (!s->DPB[i].frame)goto fail;s->DPB[i].tf.f = s->DPB[i].frame;}s->max_ra = INT_MAX;s->md5_ctx = av_md5_alloc();if (!s->md5_ctx)goto fail;ff_bswapdsp_init(&s->bdsp);s->context_initialized = 1;s->eos = 0;return 0;fail:hevc_decode_free(avctx);return AVERROR(ENOMEM);
}hevc_decode_free()
hevc_decode_free()用于关闭HEVC解码器。该函数的定义例如以下所看到的。//关闭HEVC解码器
static av_cold int hevc_decode_free(AVCodecContext *avctx)
{HEVCContext *s = avctx->priv_data;int i;pic_arrays_free(s);av_freep(&s->md5_ctx);for(i=0; i < s->nals_allocated; i++) {av_freep(&s->skipped_bytes_pos_nal[i]);}av_freep(&s->skipped_bytes_pos_size_nal);av_freep(&s->skipped_bytes_nal);av_freep(&s->skipped_bytes_pos_nal);av_freep(&s->cabac_state);av_frame_free(&s->tmp_frame);av_frame_free(&s->output_frame);for (i = 0; i < FF_ARRAY_ELEMS(s->DPB); i++) {ff_hevc_unref_frame(s, &s->DPB[i], ~0);av_frame_free(&s->DPB[i].frame);}for (i = 0; i < FF_ARRAY_ELEMS(s->vps_list); i++)av_buffer_unref(&s->vps_list[i]);for (i = 0; i < FF_ARRAY_ELEMS(s->sps_list); i++)av_buffer_unref(&s->sps_list[i]);for (i = 0; i < FF_ARRAY_ELEMS(s->pps_list); i++)av_buffer_unref(&s->pps_list[i]);s->sps = NULL;s->pps = NULL;s->vps = NULL;av_buffer_unref(&s->current_sps);av_freep(&s->sh.entry_point_offset);av_freep(&s->sh.offset);av_freep(&s->sh.size);for (i = 1; i < s->threads_number; i++) {HEVCLocalContext *lc = s->HEVClcList[i];if (lc) {av_freep(&s->HEVClcList[i]);av_freep(&s->sList[i]);}}if (s->HEVClc == s->HEVClcList[0])s->HEVClc = NULL;av_freep(&s->HEVClcList[0]);for (i = 0; i < s->nals_allocated; i++)av_freep(&s->nals[i].rbsp_buffer);av_freep(&s->nals);s->nals_allocated = 0;return 0;
}
从源码能够看出，hevc_decode_free()释放了HEVCContext中的内存。
hevc_decode_frame()
hevc_decode_frame()是HEVC解码器中最关键的函数。用于解码一帧数据。该函数的定义例如以下所看到的。
/** 解码一帧数据** 凝视：雷霄骅* leixiaohua1020@126.com* http://blog.csdn.net/leixiaohua1020**/
static int hevc_decode_frame(AVCodecContext *avctx, void *data, int *got_output,AVPacket *avpkt)
{int ret;HEVCContext *s = avctx->priv_data;//没有输入码流的时候。输出解码器中剩余数据//相应“Flush Decoder”功能if (!avpkt->size) {//第3个參数flush取值为1ret = ff_hevc_output_frame(s, data, 1);if (ret < 0)return ret;*got_output = ret;return 0;}s->ref = NULL;//解码一帧数据ret = decode_nal_units(s, avpkt->data, avpkt->size);if (ret < 0)return ret;/* verify the SEI checksum */if (avctx->err_recognition & AV_EF_CRCCHECK && s->is_decoded &&s->is_md5) {ret = verify_md5(s, s->ref->frame);if (ret < 0 && avctx->err_recognition & AV_EF_EXPLODE) {ff_hevc_unref_frame(s, s->ref, ~0);return ret;}}s->is_md5 = 0;if (s->is_decoded) {av_log(avctx, AV_LOG_DEBUG, "Decoded frame with POC %d.\n", s->poc);s->is_decoded = 0;}if (s->output_frame->buf[0]) {//输出解码后数据av_frame_move_ref(data, s->output_frame);*got_output = 1;}return avpkt->size;
}
从源码能够看出。hevc_decode_frame()依据输入的AVPacket的data是否为NULL分成两个情况：
（1）AVPacket的data为NULL的时候。代表没有输入码流。这时候直接调用ff_hevc_output_frame()输出解码器中缓存的帧。以下看一下一帧NALU的解码函数decode_nal_units()。
（2）AVPacket的data不为NULL的时候。调用decode_nal_units()解码输入的一帧数据的NALU。
decode_nal_units()
decode_nal_units()用于解码一帧NALU。该函数的定义例如以下所看到的。//解码一帧数据
static int decode_nal_units(HEVCContext *s, const uint8_t *buf, int length)
{int i, consumed, ret = 0;s->ref = NULL;s->last_eos = s->eos;s->eos = 0;/* split the input packet into NAL units, so we know the upper bound on the* number of slices in the frame */s->nb_nals = 0;while (length >= 4) {HEVCNAL *nal;int extract_length = 0;if (s->is_nalff) {int i;for (i = 0; i < s->nal_length_size; i++)extract_length = (extract_length << 8) | buf[i];buf += s->nal_length_size;length -= s->nal_length_size;if (extract_length > length) {av_log(s->avctx, AV_LOG_ERROR, "Invalid NAL unit size.\n");ret = AVERROR_INVALIDDATA;goto fail;}} else {/* search start code *///查找起始码0x000001while (buf[0] != 0 || buf[1] != 0 || buf[2] != 1) {++buf;--length;if (length < 4) {av_log(s->avctx, AV_LOG_ERROR, "No start code is found.\n");ret = AVERROR_INVALIDDATA;goto fail;}}//找到后，跳过起始码（3Byte）buf += 3;length -= 3;}if (!s->is_nalff)extract_length = length;if (s->nals_allocated < s->nb_nals + 1) {int new_size = s->nals_allocated + 1;HEVCNAL *tmp = av_realloc_array(s->nals, new_size, sizeof(*tmp));if (!tmp) {ret = AVERROR(ENOMEM);goto fail;}s->nals = tmp;memset(s->nals + s->nals_allocated, 0,(new_size - s->nals_allocated) * sizeof(*tmp));av_reallocp_array(&s->skipped_bytes_nal, new_size, sizeof(*s->skipped_bytes_nal));av_reallocp_array(&s->skipped_bytes_pos_size_nal, new_size, sizeof(*s->skipped_bytes_pos_size_nal));av_reallocp_array(&s->skipped_bytes_pos_nal, new_size, sizeof(*s->skipped_bytes_pos_nal));s->skipped_bytes_pos_size_nal[s->nals_allocated] = 1024; // initial buffer sizes->skipped_bytes_pos_nal[s->nals_allocated] = av_malloc_array(s->skipped_bytes_pos_size_nal[s->nals_allocated], sizeof(*s->skipped_bytes_pos));s->nals_allocated = new_size;}s->skipped_bytes_pos_size = s->skipped_bytes_pos_size_nal[s->nb_nals];s->skipped_bytes_pos = s->skipped_bytes_pos_nal[s->nb_nals];nal = &s->nals[s->nb_nals];consumed = ff_hevc_extract_rbsp(s, buf, extract_length, nal);s->skipped_bytes_nal[s->nb_nals] = s->skipped_bytes;s->skipped_bytes_pos_size_nal[s->nb_nals] = s->skipped_bytes_pos_size;s->skipped_bytes_pos_nal[s->nb_nals++] = s->skipped_bytes_pos;if (consumed < 0) {ret = consumed;goto fail;}ret = init_get_bits8(&s->HEVClc->gb, nal->data, nal->size);if (ret < 0)goto fail;hls_nal_unit(s);if (s->nal_unit_type == NAL_EOB_NUT ||s->nal_unit_type == NAL_EOS_NUT)s->eos = 1;buf += consumed;length -= consumed;}/* parse the NAL units */for (i = 0; i < s->nb_nals; i++) {int ret;s->skipped_bytes = s->skipped_bytes_nal[i];s->skipped_bytes_pos = s->skipped_bytes_pos_nal[i];//解码NALUret = decode_nal_unit(s, s->nals[i].data, s->nals[i].size);if (ret < 0) {av_log(s->avctx, AV_LOG_WARNING,"Error parsing NAL unit #%d.\n", i);goto fail;}}fail:if (s->ref && s->threads_type == FF_THREAD_FRAME)ff_thread_report_progress(&s->ref->tf, INT_MAX, 0);return ret;
}
从源码能够看出。decode_nal_units()中又调用了还有一个函数decode_nal_unit()，两者的名字仅仅相差一个“s”。
由此能够看出decode_nal_unit()作用是解码一个NALU。
decode_nal_unit()
decode_nal_unit()用于解码一个NALU。该函数的定义例如以下所看到的。//解码一个NALU
static int decode_nal_unit(HEVCContext *s, const uint8_t *nal, int length)
{HEVCLocalContext *lc = s->HEVClc;GetBitContext *gb = &lc->gb;int ctb_addr_ts, ret;ret = init_get_bits8(gb, nal, length);if (ret < 0)return ret;ret = hls_nal_unit(s);if (ret < 0) {av_log(s->avctx, AV_LOG_ERROR, "Invalid NAL unit %d, skipping.\n",s->nal_unit_type);goto fail;} else if (!ret)return 0;switch (s->nal_unit_type) {case NAL_VPS://解析VPSret = ff_hevc_decode_nal_vps(s);if (ret < 0)goto fail;break;case NAL_SPS://解析SPSret = ff_hevc_decode_nal_sps(s);if (ret < 0)goto fail;break;case NAL_PPS://解析PPSret = ff_hevc_decode_nal_pps(s);if (ret < 0)goto fail;break;case NAL_SEI_PREFIX:case NAL_SEI_SUFFIX://解析SEIret = ff_hevc_decode_nal_sei(s);if (ret < 0)goto fail;break;case NAL_TRAIL_R:case NAL_TRAIL_N:case NAL_TSA_N:case NAL_TSA_R:case NAL_STSA_N:case NAL_STSA_R:case NAL_BLA_W_LP:case NAL_BLA_W_RADL:case NAL_BLA_N_LP:case NAL_IDR_W_RADL:case NAL_IDR_N_LP:case NAL_CRA_NUT:case NAL_RADL_N:case NAL_RADL_R:case NAL_RASL_N:case NAL_RASL_R://解析Slice//解析Slice Headerret = hls_slice_header(s);if (ret < 0)return ret;if (s->max_ra == INT_MAX) {if (s->nal_unit_type == NAL_CRA_NUT || IS_BLA(s)) {s->max_ra = s->poc;} else {if (IS_IDR(s))s->max_ra = INT_MIN;}}if ((s->nal_unit_type == NAL_RASL_R || s->nal_unit_type == NAL_RASL_N) &&s->poc <= s->max_ra) {s->is_decoded = 0;break;} else {if (s->nal_unit_type == NAL_RASL_R && s->poc > s->max_ra)s->max_ra = INT_MIN;}if (s->sh.first_slice_in_pic_flag) {ret = hevc_frame_start(s);if (ret < 0)return ret;} else if (!s->ref) {av_log(s->avctx, AV_LOG_ERROR, "First slice in a frame missing.\n");goto fail;}if (s->nal_unit_type != s->first_nal_type) {av_log(s->avctx, AV_LOG_ERROR,"Non-matching NAL types of the VCL NALUs: %d %d\n",s->first_nal_type, s->nal_unit_type);return AVERROR_INVALIDDATA;}if (!s->sh.dependent_slice_segment_flag &&s->sh.slice_type != I_SLICE) {ret = ff_hevc_slice_rpl(s);if (ret < 0) {av_log(s->avctx, AV_LOG_WARNING,"Error constructing the reference lists for the current slice.\n");goto fail;}}//解码 Slice Dataif (s->threads_number > 1 && s->sh.num_entry_point_offsets > 0)ctb_addr_ts = hls_slice_data_wpp(s, nal, length);elsectb_addr_ts = hls_slice_data(s);if (ctb_addr_ts >= (s->sps->ctb_width * s->sps->ctb_height)) {s->is_decoded = 1;}if (ctb_addr_ts < 0) {ret = ctb_addr_ts;goto fail;}break;case NAL_EOS_NUT:case NAL_EOB_NUT:s->seq_decode = (s->seq_decode + 1) & 0xff;s->max_ra = INT_MAX;break;case NAL_AUD:case NAL_FD_NUT:break;default:av_log(s->avctx, AV_LOG_INFO,"Skipping NAL unit %d\n", s->nal_unit_type);}return 0;
fail:if (s->avctx->err_recognition & AV_EF_EXPLODE)return ret;return 0;
}
从源码能够看出。decode_nal_unit()依据不同的NALU类型调用了不同的处理函数。这些处理函数能够分为两类——解析函数和解码函数，例如以下所看到的。
（1）解析函数（获取信息）：当中解析函数在文章《FFmpeg的HEVC解码器源码简单分析：解析器（Parser）部分》已经有过介绍，就不再反复叙述了。解码函数hls_slice_data()完毕了解码Slice的工作，以下看一下该函数的定义。ff_hevc_decode_nal_vps()：解析VPS。ff_hevc_decode_nal_sps()：解析SPS。ff_hevc_decode_nal_pps()：解析PPS。ff_hevc_decode_nal_sei()：解析SEI。hls_slice_header()：解析Slice Header。（2）解码函数（解码得到图像）：hls_slice_data()：解码Slice Data。
hls_slice_data()
hls_slice_data()用于解码Slice Data。该函数的定义例如以下所看到的。//解码Slice Data
static int hls_slice_data(HEVCContext *s)
{int arg[2];int ret[2];arg[0] = 0;arg[1] = 1;//解码入口函数s->avctx->execute(s->avctx, hls_decode_entry, arg, ret , 1, sizeof(int));return ret[0];
}
能够看出该函数的源码非常easy，调用了还有一个函数hls_decode_entry()。
hls_decode_entry()
hls_decode_entry()是Slice Data解码的入口函数。该函数的定义例如以下所看到的。/** 解码入口函数** 凝视：雷霄骅* leixiaohua1020@126.com* http://blog.csdn.net/leixiaohua1020**/
static int hls_decode_entry(AVCodecContext *avctxt, void *isFilterThread)
{HEVCContext *s = avctxt->priv_data;//CTB尺寸int ctb_size = 1 << s->sps->log2_ctb_size;int more_data = 1;int x_ctb = 0;int y_ctb = 0;int ctb_addr_ts = s->pps->ctb_addr_rs_to_ts[s->sh.slice_ctb_addr_rs];if (!ctb_addr_ts && s->sh.dependent_slice_segment_flag) {av_log(s->avctx, AV_LOG_ERROR, "Impossible initial tile.\n");return AVERROR_INVALIDDATA;}if (s->sh.dependent_slice_segment_flag) {int prev_rs = s->pps->ctb_addr_ts_to_rs[ctb_addr_ts - 1];if (s->tab_slice_address[prev_rs] != s->sh.slice_addr) {av_log(s->avctx, AV_LOG_ERROR, "Previous slice segment missing\n");return AVERROR_INVALIDDATA;}}while (more_data && ctb_addr_ts < s->sps->ctb_size) {int ctb_addr_rs = s->pps->ctb_addr_ts_to_rs[ctb_addr_ts];//CTB的位置x和yx_ctb = (ctb_addr_rs % ((s->sps->width + ctb_size - 1) >> s->sps->log2_ctb_size)) << s->sps->log2_ctb_size;y_ctb = (ctb_addr_rs / ((s->sps->width + ctb_size - 1) >> s->sps->log2_ctb_size)) << s->sps->log2_ctb_size;//初始化周围的參数hls_decode_neighbour(s, x_ctb, y_ctb, ctb_addr_ts);//初始化CABACff_hevc_cabac_init(s, ctb_addr_ts);//样点自适应补偿參数hls_sao_param(s, x_ctb >> s->sps->log2_ctb_size, y_ctb >> s->sps->log2_ctb_size);s->deblock[ctb_addr_rs].beta_offset = s->sh.beta_offset;s->deblock[ctb_addr_rs].tc_offset = s->sh.tc_offset;s->filter_slice_edges[ctb_addr_rs] = s->sh.slice_loop_filter_across_slices_enabled_flag;/** CU示意图** 64x64块** 深度d=0* split_flag=1时候划分为4个32x32** +--------+--------+--------+--------+--------+--------+--------+--------+* | |* | | |* | |* + | +* | |* | | |* | |* + | +* | |* | | |* | |* + | +* | |* | | |* | |* + -- -- -- -- -- -- -- -- --+ -- -- -- -- -- -- -- -- --+* | | |* | |* | | |* + +* | | |* | |* | | |* + +* | | |* | |* | | |* + +* | | |* | |* | | |* +--------+--------+--------+--------+--------+--------+--------+--------+*** 32x32 块* 深度d=1* split_flag=1时候划分为4个16x16** +--------+--------+--------+--------+* | |* | | |* | |* + | +* | |* | | |* | |* + -- -- -- -- + -- -- -- -- +* | |* | | |* | |* + | +* | |* | | |* | |* +--------+--------+--------+--------+*** 16x16 块* 深度d=2* split_flag=1时候划分为4个8x8** +--------+--------+* | |* | | |* | |* + -- --+ -- -- +* | |* | | |* | |* +--------+--------+*** 8x8块* 深度d=3* split_flag=1时候划分为4个4x4** +----+----+* | | |* + -- + -- +* | | |* +----+----+**//** 解析四叉树结构。而且解码** hls_coding_quadtree(HEVCContext *s, int x0, int y0, int log2_cb_size, int cb_depth)中：* s：HEVCContext上下文结构体* x_ctb：CB位置的x坐标* y_ctb：CB位置的y坐标* log2_cb_size：CB大小取log2之后的值* cb_depth：深度**/more_data = hls_coding_quadtree(s, x_ctb, y_ctb, s->sps->log2_ctb_size, 0);if (more_data < 0) {s->tab_slice_address[ctb_addr_rs] = -1;return more_data;}ctb_addr_ts++;//保存解码信息以供下次使用ff_hevc_save_states(s, ctb_addr_ts);//去块效应滤波ff_hevc_hls_filters(s, x_ctb, y_ctb, ctb_size);}if (x_ctb + ctb_size >= s->sps->width &&y_ctb + ctb_size >= s->sps->height)ff_hevc_hls_filter(s, x_ctb, y_ctb, ctb_size);return ctb_addr_ts;
}
从源码能够看出。hls_decode_entry()以CTB为单位处理输入的视频流。每一个CTB的压缩数据经过以下两个基本步骤进行处理：
（1）调用hls_coding_quadtree()对CTB解码。当中包括了CU、PU、TU的解码。hls_decode_entry()的函数调用关系例如以下图所看到的。
（2）调用ff_hevc_hls_filters()进行滤波。当中包括去块效应滤波和SAO滤波。
兴许的几篇文章将会对其调用的函数进行分析。
至此。FFmpeg HEVC解码器的主干部分的源码就分析完毕了。
雷霄骅
leixiaohua1020@126.com
http://blog.csdn.net/leixiaohua1020
