HEVCContext和HEVCFrame是ffmpeg的HEVC解碼中非常重要的結構體。

首先來看下HEVCContext，定義位於libavcodec\Hevc.h中。程式碼如下：

typedef struct HEVCContext {
    const AVClass *c;  // needed by private avoptions
    AVCodecContext *avctx;

    struct HEVCContext  *sList[MAX_NB_THREADS];

    HEVCLocalContext    *HEVClcList[MAX_NB_THREADS];
    HEVCLocalContext    *HEVClc;

    uint8_t             threads_type;
    uint8_t             threads_number;

    int                 width;
    int                 height;

    uint8_t *cabac_state;

    /** 1 if the independent slice segment header was successfully parsed */
    uint8_t slice_initialized;

    AVFrame *frame;
    AVFrame *output_frame;
    uint8_t *sao_pixel_buffer_h[3];
    uint8_t *sao_pixel_buffer_v[3];

    HEVCParamSets ps;

    AVBufferPool *tab_mvf_pool;
    AVBufferPool *rpl_tab_pool;

    ///< candidate references for the current frame
    RefPicList rps[5];

    SliceHeader sh;
    SAOParams *sao;
    DBParams *deblock;
    enum NALUnitType nal_unit_type;
    int temporal_id;  ///< temporal_id_plus1 - 1
    HEVCFrame *ref;
    HEVCFrame DPB[32];
    int poc;
    int pocTid0;
    int slice_idx; ///< number of the slice being currently decoded
    int eos;       ///< current packet contains an EOS/EOB NAL
    int last_eos;  ///< last packet contains an EOS/EOB NAL
    int max_ra;
    int bs_width;
    int bs_height;

    int is_decoded;
    int no_rasl_output_flag;

    HEVCPredContext hpc;
    HEVCDSPContext hevcdsp;
    VideoDSPContext vdsp;
    BswapDSPContext bdsp;
    int8_t *qp_y_tab;
    uint8_t *horizontal_bs;
    uint8_t *vertical_bs;

    int32_t *tab_slice_address;

    //  CU
    uint8_t *skip_flag;
    uint8_t *tab_ct_depth;
    // PU
    uint8_t *tab_ipm;

    uint8_t *cbf_luma; // cbf_luma of colocated TU
    uint8_t *is_pcm;

    // CTB-level flags affecting loop filter operation
    uint8_t *filter_slice_edges;

    /** used on BE to byteswap the lines for checksumming */
    uint8_t *checksum_buf;
    int      checksum_buf_size;

    /**
     * Sequence counters for decoded and output frames, so that old
     * frames are output first after a POC reset
     */
    uint16_t seq_decode;
    uint16_t seq_output;

    int enable_parallel_tiles;
    int wpp_err;

    const uint8_t *data;

    HEVCPacket pkt;
    // type of the first VCL NAL of the current frame
    enum NALUnitType first_nal_type;

    // for checking the frame checksums
    struct AVMD5 *md5_ctx;
    uint8_t       md5[3][16];
    uint8_t is_md5;

    uint8_t context_initialized;
    uint8_t is_nalff;       ///< this flag is != 0 if bitstream is encapsulated
                            ///< as a format defined in 14496-15
    int apply_defdispwin;

    int active_seq_parameter_set_id;

    int nal_length_size;    ///< Number of bytes used for nal length (1, 2 or 4)
    int nuh_layer_id;

    /** frame packing arrangement variables */
    int sei_frame_packing_present;
    int frame_packing_arrangement_type;
    int content_interpretation_type;
    int quincunx_subsampling;

    /** display orientation */
    int sei_display_orientation_present;
    int sei_anticlockwise_rotation;
    int sei_hflip, sei_vflip;

    int picture_struct;
} HEVCContext;
 

AVCodecContext *avctx：對應的codec上下文。

int width，height：影象寬高。

uint8_t *cabac_state：cabac的狀態，算數編碼相關。

uint8_t slice_initialized：根據註釋，當解碼到independent slice segment header時，置為1。

AVFrame *frame，*output_frame：影象儲存結構體。

uint8_t *sao_pixel_buffer_h[3]，sao_pixel_buffer_v[3]：SAO相關。

HEVCParamSets ps

AVBufferPool *tab_mvf_pool：運動向量相關的buffer pool。

AVBufferPool *rpl_tab_pool：reference picture list的buffer pool。

RefPicList rps[5]：5個refPicList的candidate表格，在rps計算中使用。

SliceHeader sh：slice header結構體，儲存slice header的資訊。

SAOParams *sao：SAO的相關引數。

DBParams *deblock

enum NALUnitType nal_unit_type：當前NAL的型別。

HEVCFrame *ref：存放參考幀，有待進一步的研究。

HEVCFrame DPB[32]：DecodePicBuffer。

int poc：picture order count

HEVCPredContext hpc：幀內預測上下文，包含intra pred的相關函式，之後會詳細分析。

HEVCDSPContext hevcdsp：編解碼計算上下文，包括變換，差值，濾波，SAO等的相關函式。

int8_t *qp_y_tab：存放亮度QP

uint8_t *horizontal_bs，*vertical_bs：水平和垂直方向的濾波強度。

int32_t *tab_slice_address：slice地址。

uint8_t *skip_flag：CU是否skip。

uint8_t *tab_ct_depth：CU的depth。

uint8_t *tab_ipm：存放intra pred mode

HEVCPacket pkt：存放packet資訊的結構體，其中包含成員HEVCNAL *nals，存放packet中所有的nalu的資訊。

enum NALUnitType first_nal_type：當前幀的第一個nal的型別。

結構體HECVFrame位於位於libavcodec\Hevc.h中。程式碼如下：

typedef struct HEVCFrame {
    AVFrame *frame;
    ThreadFrame tf;
    MvField *tab_mvf;
    RefPicList *refPicList;
    RefPicListTab **rpl_tab;
    int ctb_count;
    int poc;
    struct HEVCFrame *collocated_ref;

    HEVCWindow window;

    AVBufferRef *tab_mvf_buf;
    AVBufferRef *rpl_tab_buf;
    AVBufferRef *rpl_buf;

    AVBufferRef *hwaccel_priv_buf;
    void *hwaccel_picture_private;

    /**
     * A sequence counter, so that old frames are output first
     * after a POC reset
     */
    uint16_t sequence;

    /**
     * A combination of HEVC_FRAME_FLAG_*
     */
    uint8_t flags;
} HEVCFrame;

MvField *tab_mvf：運動向量的tab

RefPicList *refPicList：備選參考幀的list

RefPicListTab **rpl_tab：備選參考幀的tab，（一個tab含有list0，list1）

int ctb_count：coding tree block的計數。

struct HEVCFrame *collocated_ref：collocated的參考幀

int poc：當前幀的poc