cavsdec.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

                        MV_PRED_MEDIAN, BLK_8X8, 1);
                break;
            case B_SUB_SYM:
                ff_cavs_mv(h, mv_scan[block], mv_scan[block]-3,
                        MV_PRED_MEDIAN, BLK_8X8, 1);
                mv_pred_sym(h, &h->mv[mv_scan[block]], BLK_8X8);
                break;
            }
        }
        for(block=0;block<4;block++) {
            if(sub_type[block] == B_SUB_BWD)
                ff_cavs_mv(h, mv_scan[block]+MV_BWD_OFFS,
                        mv_scan[block]+MV_BWD_OFFS-3,
                        MV_PRED_MEDIAN, BLK_8X8, 0);
        }
        break;
    default:
        assert((mb_type > B_SYM_16X16) && (mb_type < B_8X8));
        flags = ff_cavs_partition_flags[mb_type];
        if(mb_type & 1) { /* 16x8 macroblock types */
            if(flags & FWD0)
                ff_cavs_mv(h, MV_FWD_X0, MV_FWD_C2, MV_PRED_TOP,  BLK_16X8, 1);
            if(flags & SYM0)
                mv_pred_sym(h, &h->mv[MV_FWD_X0], BLK_16X8);
            if(flags & FWD1)
                ff_cavs_mv(h, MV_FWD_X2, MV_FWD_A1, MV_PRED_LEFT, BLK_16X8, 1);
            if(flags & SYM1)
                mv_pred_sym(h, &h->mv[MV_FWD_X2], BLK_16X8);
            if(flags & BWD0)
                ff_cavs_mv(h, MV_BWD_X0, MV_BWD_C2, MV_PRED_TOP,  BLK_16X8, 0);
            if(flags & BWD1)
                ff_cavs_mv(h, MV_BWD_X2, MV_BWD_A1, MV_PRED_LEFT, BLK_16X8, 0);
        } else {          /* 8x16 macroblock types */
            if(flags & FWD0)
                ff_cavs_mv(h, MV_FWD_X0, MV_FWD_B3, MV_PRED_LEFT, BLK_8X16, 1);
            if(flags & SYM0)
                mv_pred_sym(h, &h->mv[MV_FWD_X0], BLK_8X16);
            if(flags & FWD1)
                ff_cavs_mv(h,MV_FWD_X1,MV_FWD_C2,MV_PRED_TOPRIGHT,BLK_8X16,1);
            if(flags & SYM1)
                mv_pred_sym(h, &h->mv[MV_FWD_X1], BLK_8X16);
            if(flags & BWD0)
                ff_cavs_mv(h, MV_BWD_X0, MV_BWD_B3, MV_PRED_LEFT, BLK_8X16, 0);
            if(flags & BWD1)
                ff_cavs_mv(h,MV_BWD_X1,MV_BWD_C2,MV_PRED_TOPRIGHT,BLK_8X16,0);
        }
    }
    ff_cavs_inter(h, mb_type);
    set_intra_mode_default(h);
    if(mb_type != B_SKIP)
        decode_residual_inter(h);
    ff_cavs_filter(h,mb_type);
}

/*****************************************************************************
 *
 * slice level
 *
 ****************************************************************************/

static inline int decode_slice_header(AVSContext *h, GetBitContext *gb) {
    if(h->stc > 0xAF)
        av_log(h->s.avctx, AV_LOG_ERROR, "unexpected start code 0x%02x\n", h->stc);
    h->mby = h->stc;
    if((h->mby == 0) && (!h->qp_fixed)){
        h->qp_fixed = get_bits1(gb);
        h->qp = get_bits(gb,6);
    }
    /* inter frame or second slice can have weighting params */
    if((h->pic_type != FF_I_TYPE) || (!h->pic_structure && h->mby >= h->mb_width/2))
        if(get_bits1(gb)) { //slice_weighting_flag
            av_log(h->s.avctx, AV_LOG_ERROR,
                   "weighted prediction not yet supported\n");
        }
    return 0;
}

static inline void check_for_slice(AVSContext *h) {
    GetBitContext *gb = &h->s.gb;
    int align;
    align = (-get_bits_count(gb)) & 7;
    if((show_bits_long(gb,24+align) & 0xFFFFFF) == 0x000001) {
        skip_bits_long(gb,24+align);
        h->stc = get_bits(gb,8);
        decode_slice_header(h,gb);
    }
}

/*****************************************************************************
 *
 * frame level
 *
 ****************************************************************************/

static int decode_pic(AVSContext *h) {
    MpegEncContext *s = &h->s;
    int skip_count;
    enum mb_t mb_type;

    if (!s->context_initialized) {
        s->avctx->idct_algo = FF_IDCT_CAVS;
        if (MPV_common_init(s) < 0)
            return -1;
        ff_init_scantable(s->dsp.idct_permutation,&h->scantable,ff_zigzag_direct);
    }
    skip_bits(&s->gb,16);//bbv_dwlay
    if(h->stc == PIC_PB_START_CODE) {
        h->pic_type = get_bits(&s->gb,2) + FF_I_TYPE;
        if(h->pic_type > FF_B_TYPE) {
            av_log(s->avctx, AV_LOG_ERROR, "illegal picture type\n");
            return -1;
        }
        /* make sure we have the reference frames we need */
        if(!h->DPB[0].data[0] ||
          (!h->DPB[1].data[0] && h->pic_type == FF_B_TYPE))
            return -1;
    } else {
        h->pic_type = FF_I_TYPE;
        if(get_bits1(&s->gb))
            skip_bits(&s->gb,16);//time_code
    }
    /* release last B frame */
    if(h->picture.data[0])
        s->avctx->release_buffer(s->avctx, (AVFrame *)&h->picture);

    s->avctx->get_buffer(s->avctx, (AVFrame *)&h->picture);
    ff_cavs_init_pic(h);
    h->picture.poc = get_bits(&s->gb,8)*2;

    /* get temporal distances and MV scaling factors */
    if(h->pic_type != FF_B_TYPE) {
        h->dist[0] = (h->picture.poc - h->DPB[0].poc  + 512) % 512;
    } else {
        h->dist[0] = (h->DPB[0].poc  - h->picture.poc + 512) % 512;
    }
    h->dist[1] = (h->picture.poc - h->DPB[1].poc  + 512) % 512;
    h->scale_den[0] = h->dist[0] ? 512/h->dist[0] : 0;
    h->scale_den[1] = h->dist[1] ? 512/h->dist[1] : 0;
    if(h->pic_type == FF_B_TYPE) {
        h->sym_factor = h->dist[0]*h->scale_den[1];
    } else {
        h->direct_den[0] = h->dist[0] ? 16384/h->dist[0] : 0;
        h->direct_den[1] = h->dist[1] ? 16384/h->dist[1] : 0;
    }

    if(s->low_delay)
        get_ue_golomb(&s->gb); //bbv_check_times
    h->progressive             = get_bits1(&s->gb);
    if(h->progressive)
        h->pic_structure = 1;
    else if(!(h->pic_structure = get_bits1(&s->gb) && (h->stc == PIC_PB_START_CODE)) )
        skip_bits1(&s->gb);     //advanced_pred_mode_disable
    skip_bits1(&s->gb);        //top_field_first
    skip_bits1(&s->gb);        //repeat_first_field
    h->qp_fixed                = get_bits1(&s->gb);
    h->qp                      = get_bits(&s->gb,6);
    if(h->pic_type == FF_I_TYPE) {
        if(!h->progressive && !h->pic_structure)
            skip_bits1(&s->gb);//what is this?
        skip_bits(&s->gb,4);   //reserved bits
    } else {
        if(!(h->pic_type == FF_B_TYPE && h->pic_structure == 1))
            h->ref_flag        = get_bits1(&s->gb);
        skip_bits(&s->gb,4);   //reserved bits
        h->skip_mode_flag      = get_bits1(&s->gb);
    }
    h->loop_filter_disable     = get_bits1(&s->gb);
    if(!h->loop_filter_disable && get_bits1(&s->gb)) {
        h->alpha_offset        = get_se_golomb(&s->gb);
        h->beta_offset         = get_se_golomb(&s->gb);
    } else {
        h->alpha_offset = h->beta_offset  = 0;
    }
    check_for_slice(h);
    if(h->pic_type == FF_I_TYPE) {
        do {
            decode_mb_i(h, 0);
        } while(ff_cavs_next_mb(h));
    } else if(h->pic_type == FF_P_TYPE) {
        do {
            if(h->skip_mode_flag) {
                skip_count = get_ue_golomb(&s->gb);
                while(skip_count--) {
                    decode_mb_p(h,P_SKIP);
                    if(!ff_cavs_next_mb(h))
                        goto done;
                }
                mb_type = get_ue_golomb(&s->gb) + P_16X16;
            } else
                mb_type = get_ue_golomb(&s->gb) + P_SKIP;
            if(mb_type > P_8X8) {
                decode_mb_i(h, mb_type - P_8X8 - 1);
            } else
                decode_mb_p(h,mb_type);
        } while(ff_cavs_next_mb(h));
    } else { /* FF_B_TYPE */
        do {
            if(h->skip_mode_flag) {
                skip_count = get_ue_golomb(&s->gb);
                while(skip_count--) {
                    decode_mb_b(h,B_SKIP);
                    if(!ff_cavs_next_mb(h))
                        goto done;
                }
                mb_type = get_ue_golomb(&s->gb) + B_DIRECT;
            } else
                mb_type = get_ue_golomb(&s->gb) + B_SKIP;
            if(mb_type > B_8X8) {
                decode_mb_i(h, mb_type - B_8X8 - 1);
            } else
                decode_mb_b(h,mb_type);
        } while(ff_cavs_next_mb(h));
    }
 done:
    if(h->pic_type != FF_B_TYPE) {
        if(h->DPB[1].data[0])
            s->avctx->release_buffer(s->avctx, (AVFrame *)&h->DPB[1]);
        memcpy(&h->DPB[1], &h->DPB[0], sizeof(Picture));
        memcpy(&h->DPB[0], &h->picture, sizeof(Picture));
        memset(&h->picture,0,sizeof(Picture));
    }
    return 0;
}

/*****************************************************************************
 *
 * headers and interface
 *
 ****************************************************************************/

static int decode_seq_header(AVSContext *h) {
    MpegEncContext *s = &h->s;
    int frame_rate_code;

    h->profile =         get_bits(&s->gb,8);
    h->level =           get_bits(&s->gb,8);
    skip_bits1(&s->gb); //progressive sequence
    s->width =           get_bits(&s->gb,14);
    s->height =          get_bits(&s->gb,14);
    skip_bits(&s->gb,2); //chroma format
    skip_bits(&s->gb,3); //sample_precision
    h->aspect_ratio =    get_bits(&s->gb,4);
    frame_rate_code =    get_bits(&s->gb,4);
    skip_bits(&s->gb,18);//bit_rate_lower
    skip_bits1(&s->gb);  //marker_bit
    skip_bits(&s->gb,12);//bit_rate_upper
    s->low_delay =       get_bits1(&s->gb);
    h->mb_width  = (s->width  + 15) >> 4;
    h->mb_height = (s->height + 15) >> 4;
    h->s.avctx->time_base.den = ff_frame_rate_tab[frame_rate_code].num;
    h->s.avctx->time_base.num = ff_frame_rate_tab[frame_rate_code].den;
    h->s.avctx->width  = s->width;
    h->s.avctx->height = s->height;
    if(!h->top_qp)
        ff_cavs_init_top_lines(h);
    return 0;
}

static void cavs_flush(AVCodecContext * avctx) {
    AVSContext *h = avctx->priv_data;
    h->got_keyframe = 0;
}

static int cavs_decode_frame(AVCodecContext * avctx,void *data, int *data_size,
                             uint8_t * buf, int buf_size) {
    AVSContext *h = avctx->priv_data;
    MpegEncContext *s = &h->s;
    int input_size;
    const uint8_t *buf_end;
    const uint8_t *buf_ptr;
    AVFrame *picture = data;
    uint32_t stc = -1;

    s->avctx = avctx;

    if (buf_size == 0) {
        if(!s->low_delay && h->DPB[0].data[0]) {
            *data_size = sizeof(AVPicture);
            *picture = *(AVFrame *) &h->DPB[0];
        }
        return 0;
    }

    buf_ptr = buf;
    buf_end = buf + buf_size;
    for(;;) {
        buf_ptr = ff_find_start_code(buf_ptr,buf_end, &stc);
        if(stc & 0xFFFFFE00)
            return FFMAX(0, buf_ptr - buf - s->parse_context.last_index);
        input_size = (buf_end - buf_ptr)*8;
        switch(stc) {
        case CAVS_START_CODE:
            init_get_bits(&s->gb, buf_ptr, input_size);
            decode_seq_header(h);
            break;
        case PIC_I_START_CODE:
            if(!h->got_keyframe) {
                if(h->DPB[0].data[0])
                    avctx->release_buffer(avctx, (AVFrame *)&h->DPB[0]);
                if(h->DPB[1].data[0])
                    avctx->release_buffer(avctx, (AVFrame *)&h->DPB[1]);
                h->got_keyframe = 1;
            }
        case PIC_PB_START_CODE:
            *data_size = 0;
            if(!h->got_keyframe)
                break;
            init_get_bits(&s->gb, buf_ptr, input_size);
            h->stc = stc;
            if(decode_pic(h))
                break;
            *data_size = sizeof(AVPicture);
            if(h->pic_type != FF_B_TYPE) {
                if(h->DPB[1].data[0]) {
                    *picture = *(AVFrame *) &h->DPB[1];
                } else {
                    *data_size = 0;
                }
            } else
                *picture = *(AVFrame *) &h->picture;
            break;
        case EXT_START_CODE:
            //mpeg_decode_extension(avctx,buf_ptr, input_size);
            break;
        case USER_START_CODE:
            //mpeg_decode_user_data(avctx,buf_ptr, input_size);
            break;
        default:
            if (stc >= SLICE_MIN_START_CODE &&
                stc <= SLICE_MAX_START_CODE) {
                init_get_bits(&s->gb, buf_ptr, input_size);
                decode_slice_header(h, &s->gb);
            }
            break;
        }
    }
}

AVCodec cavs_decoder = {
    "cavs",
    CODEC_TYPE_VIDEO,
    CODEC_ID_CAVS,
    sizeof(AVSContext),
    ff_cavs_init,
    NULL,
    ff_cavs_end,
    cavs_decode_frame,
    CODEC_CAP_DR1 | CODEC_CAP_DELAY,
    .flush= cavs_flush,
};