FFmpeg的HEVC解码器源代码简单分析：解码器主干部分
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HEVC源代码分析文章列表：
【解码 -libavcodec HEVC 解码器】
FFmpeg的HEVC解码器源代码简单分析：概述
FFmpeg的HEVC解码器源代码简单分析：解析器（Parser）部分
FFmpeg的HEVC解码器源代码简单分析：解码器主干部分
FFmpeg的HEVC解码器源代码简单分析：CTU解码（CTU Decode）部分-PU
FFmpeg的HEVC解码器源代码简单分析：CTU解码（CTU Decode）部分-TU
FFmpeg的HEVC解码器源代码简单分析：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。它包含了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，主要包含了“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解码器中的位置如下图所示。
单击查看更清晰的大图
HEVC解码器主干部分的源代码的调用关系如下图所示。
单击查看更清晰的大图
从图中可以看出，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()。其中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；另一方面调用了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()，在其中完成了Slice Data解码的流程。该流程包含了CU、PU、TU解码，环路滤波、SAO滤波等环节。
ff_hevc_decoder
ff_hevc_decoder是HEVC解码器对应的AVCodec结构体。该结构体的定义位于libavcodec\hevc.c，如下所示。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),
};从源代码可以看出，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()。
hevc_decode_init()
hevc_decode_init()用于初始化HEVC解码器。该函数的定义如下。//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CABAC
ff_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;
else
s->threads_number = 1;
//如果AVCodecContext中包含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;
else
s->threads_type = FF_THREAD_SLICE;
return 0;
}
从源代码中可以看出，hevc_decode_init()对HEVCContext中的变量做了一些初始化工作。其中调用了一个函数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。该函数的定义如下所示。//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。该函数的定义如下所示。//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;
}
从源代码可以看出，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。该函数的定义如下所示。/* * 解码一帧数据 * * 注释：雷霄骅 * [email protected] * 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 //对应“Flush Decoder”功能 if (!avpkt->size) { //第3个参数flush取值为1 ret = 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; }
从源代码可以看出，hevc_decode_frame()根据输入的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。下面看一下一帧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。该函数的定义如下所示。//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0x000001
while (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 size
s->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NALU
ret = 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;
}
从源代码可以看出，decode_nal_units()中又调用了另一个函数decode_nal_unit()，两者的名字只相差一个“s”。由此可以看出decode_nal_unit()作用是解码一个NALU。
decode_nal_unit()
decode_nal_unit()用于解码一个NALU。该函数的定义如下所示。//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VPS
ret = ff_hevc_decode_nal_vps(s);
if (ret < 0)
goto fail;
break;
case NAL_SPS:
//解析SPS
ret = ff_hevc_decode_nal_sps(s);
if (ret < 0)
goto fail;
break;
case NAL_PPS:
//解析PPS
ret = ff_hevc_decode_nal_pps(s);
if (ret < 0)
goto fail;
break;
case NAL_SEI_PREFIX:
case NAL_SEI_SUFFIX:
//解析SEI
ret = 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 Header
ret = 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 Data
if (s->threads_number > 1 && s->sh.num_entry_point_offsets > 0)
ctb_addr_ts = hls_slice_data_wpp(s, nal, length);
else
ctb_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;
}
从源代码可以看出，decode_nal_unit()根据不同的NALU类型调用了不同的处理函数。这些处理函数可以分为两类——解析函数和解码函数，如下所示。
（1）解析函数（获取信息）：其中解析函数在文章《FFmpeg的HEVC解码器源代码简单分析：解析器（Parser）部分》已经有过介绍，就不再重复叙述了。解码函数hls_slice_data()完成了解码Slice的工作，下面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。该函数的定义如下所示。//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];
}
可以看出该函数的源代码很简单，调用了另一个函数hls_decode_entry()。
hls_decode_entry()
hls_decode_entry()是Slice Data解码的入口函数。该函数的定义如下所示。/* * 解码入口函数 * * 注释：雷霄骅 * [email protected] * 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y x_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; //初始化周围的参数 hls_decode_neighbour(s, x_ctb, y_ctb, ctb_addr_ts); //初始化CABAC ff_hevc_cabac_init(s, ctb_addr_ts); //样点自适应补偿参数 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，并且解码 * * 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; }
从源代码可以看出，hls_decode_entry()以CTB为单位处理输入的视频流。每个CTB的压缩数据经过下面两个基本步骤进行处理：
（1）调用hls_coding_quadtree()对CTB解码。其中包括了CU、PU、TU的解码。hls_decode_entry()的函数调用关系如下图所示。后续的几篇文章将会对其调用的函数进行分析。
（2）调用ff_hevc_hls_filters()进行滤波。其中包括去块效应滤波和SAO滤波。
至此，FFmpeg HEVC解码器的主干部分的源代码就分析完毕了。
雷霄骅
[email protected]
http://blog.csdn.net/leixiaohua1020