msmpeg4.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

        if(start_code!=0x00000100){
            av_log(s->avctx, AV_LOG_ERROR, "invalid startcode\n");
            return -1;
        }

        num= get_bits(&s->gb, 5); // frame number */
    }

    s->pict_type = get_bits(&s->gb, 2) + 1;
    if (s->pict_type != I_TYPE &&
        s->pict_type != P_TYPE){
        av_log(s->avctx, AV_LOG_ERROR, "invalid picture type\n");
        return -1;
    }
#if 0
{
    static int had_i=0;
    if(s->pict_type == I_TYPE) had_i=1;
    if(!had_i) return -1;
}
#endif
    s->chroma_qscale= s->qscale = get_bits(&s->gb, 5);
    if(s->qscale==0){
        av_log(s->avctx, AV_LOG_ERROR, "invalid qscale\n");
        return -1;
    }

    if (s->pict_type == I_TYPE) {
        code = get_bits(&s->gb, 5);
        if(s->msmpeg4_version==1){
            if(code==0 || code>s->mb_height){
                av_log(s->avctx, AV_LOG_ERROR, "invalid slice height %d\n", code);
                return -1;
            }

            s->slice_height = code;
        }else{
            /* 0x17: one slice, 0x18: two slices, ... */
            if (code < 0x17){
                av_log(s->avctx, AV_LOG_ERROR, "error, slice code was %X\n", code);
                return -1;
            }

            s->slice_height = s->mb_height / (code - 0x16);
        }

        switch(s->msmpeg4_version){
        case 1:
        case 2:
            s->rl_chroma_table_index = 2;
            s->rl_table_index = 2;

            s->dc_table_index = 0; //not used
            break;
        case 3:
            s->rl_chroma_table_index = decode012(&s->gb);
            s->rl_table_index = decode012(&s->gb);

            s->dc_table_index = get_bits1(&s->gb);
            break;
        case 4:
            msmpeg4_decode_ext_header(s, (2+5+5+17+7)/8);

            if(s->bit_rate > MBAC_BITRATE) s->per_mb_rl_table= get_bits1(&s->gb);
            else                           s->per_mb_rl_table= 0;

            if(!s->per_mb_rl_table){
                s->rl_chroma_table_index = decode012(&s->gb);
                s->rl_table_index = decode012(&s->gb);
            }

            s->dc_table_index = get_bits1(&s->gb);
            s->inter_intra_pred= 0;
            break;
        }
        s->no_rounding = 1;
        if(s->avctx->debug&FF_DEBUG_PICT_INFO)
            av_log(s->avctx, AV_LOG_DEBUG, "qscale:%d rlc:%d rl:%d dc:%d mbrl:%d slice:%d   \n",
                s->qscale,
                s->rl_chroma_table_index,
                s->rl_table_index,
                s->dc_table_index,
                s->per_mb_rl_table,
                s->slice_height);
    } else {
        switch(s->msmpeg4_version){
        case 1:
        case 2:
            if(s->msmpeg4_version==1)
                s->use_skip_mb_code = 1;
            else
                s->use_skip_mb_code = get_bits1(&s->gb);
            s->rl_table_index = 2;
            s->rl_chroma_table_index = s->rl_table_index;
            s->dc_table_index = 0; //not used
            s->mv_table_index = 0;
            break;
        case 3:
            s->use_skip_mb_code = get_bits1(&s->gb);
            s->rl_table_index = decode012(&s->gb);
            s->rl_chroma_table_index = s->rl_table_index;

            s->dc_table_index = get_bits1(&s->gb);

            s->mv_table_index = get_bits1(&s->gb);
            break;
        case 4:
            s->use_skip_mb_code = get_bits1(&s->gb);

            if(s->bit_rate > MBAC_BITRATE) s->per_mb_rl_table= get_bits1(&s->gb);
            else                           s->per_mb_rl_table= 0;

            if(!s->per_mb_rl_table){
                s->rl_table_index = decode012(&s->gb);
                s->rl_chroma_table_index = s->rl_table_index;
            }

            s->dc_table_index = get_bits1(&s->gb);

            s->mv_table_index = get_bits1(&s->gb);
            s->inter_intra_pred= (s->width*s->height < 320*240 && s->bit_rate<=II_BITRATE);
            break;
        }

        if(s->avctx->debug&FF_DEBUG_PICT_INFO)
            av_log(s->avctx, AV_LOG_DEBUG, "skip:%d rl:%d rlc:%d dc:%d mv:%d mbrl:%d qp:%d   \n",
                s->use_skip_mb_code,
                s->rl_table_index,
                s->rl_chroma_table_index,
                s->dc_table_index,
                s->mv_table_index,
                s->per_mb_rl_table,
                s->qscale);

        if(s->flipflop_rounding){
            s->no_rounding ^= 1;
        }else{
            s->no_rounding = 0;
        }
    }
//printf("%d %d %d %d %d\n", s->pict_type, s->bit_rate, s->inter_intra_pred, s->width, s->height);

    s->esc3_level_length= 0;
    s->esc3_run_length= 0;

#ifdef DEBUG
    av_log(s->avctx, AV_LOG_DEBUG, "*****frame %d:\n", frame_count++);
#endif
    return 0;
}

int msmpeg4_decode_ext_header(MpegEncContext * s, int buf_size)
{
    int left= buf_size*8 - get_bits_count(&s->gb);
    int length= s->msmpeg4_version>=3 ? 17 : 16;
    /* the alt_bitstream reader could read over the end so we need to check it */
    if(left>=length && left<length+8)
    {
        int fps;

        fps= get_bits(&s->gb, 5);
        s->bit_rate= get_bits(&s->gb, 11)*1024;
        if(s->msmpeg4_version>=3)
            s->flipflop_rounding= get_bits1(&s->gb);
        else
            s->flipflop_rounding= 0;

//        printf("fps:%2d bps:%2d roundingType:%1d\n", fps, s->bit_rate/1024, s->flipflop_rounding);
    }
    else if(left<length+8)
    {
        s->flipflop_rounding= 0;
        if(s->msmpeg4_version != 2)
            av_log(s->avctx, AV_LOG_ERROR, "ext header missing, %d left\n", left);
    }
    else
    {
        av_log(s->avctx, AV_LOG_ERROR, "I frame too long, ignoring ext header\n");
    }

    return 0;
}

static inline void msmpeg4_memsetw(short *tab, int val, int n)
{
    int i;
    for(i=0;i<n;i++)
        tab[i] = val;
}

#ifdef CONFIG_ENCODERS
static void msmpeg4v2_encode_motion(MpegEncContext * s, int val)
{
    int range, bit_size, sign, code, bits;

    if (val == 0) {
        /* zero vector */
        code = 0;
        put_bits(&s->pb, mvtab[code][1], mvtab[code][0]);
    } else {
        bit_size = s->f_code - 1;
        range = 1 << bit_size;
        if (val <= -64)
            val += 64;
        else if (val >= 64)
            val -= 64;

        if (val >= 0) {
            sign = 0;
        } else {
            val = -val;
            sign = 1;
        }
        val--;
        code = (val >> bit_size) + 1;
        bits = val & (range - 1);

        put_bits(&s->pb, mvtab[code][1] + 1, (mvtab[code][0] << 1) | sign);
        if (bit_size > 0) {
            put_bits(&s->pb, bit_size, bits);
        }
    }
}
#endif

/* This is identical to h263 except that its range is multiplied by 2. */
static int msmpeg4v2_decode_motion(MpegEncContext * s, int pred, int f_code)
{
    int code, val, sign, shift;

    code = get_vlc2(&s->gb, v2_mv_vlc.table, V2_MV_VLC_BITS, 2);
//     printf("MV code %d at %d %d pred: %d\n", code, s->mb_x,s->mb_y, pred);
    if (code < 0)
        return 0xffff;

    if (code == 0)
        return pred;
    sign = get_bits1(&s->gb);
    shift = f_code - 1;
    val = code;
    if (shift) {
        val = (val - 1) << shift;
        val |= get_bits(&s->gb, shift);
        val++;
    }
    if (sign)
        val = -val;

    val += pred;
    if (val <= -64)
        val += 64;
    else if (val >= 64)
        val -= 64;

    return val;
}

static int msmpeg4v12_decode_mb(MpegEncContext *s, DCTELEM block[6][64])
{
    int cbp, code, i;

    if (s->pict_type == P_TYPE) {
        if (s->use_skip_mb_code) {
            if (get_bits1(&s->gb)) {
                /* skip mb */
                s->mb_intra = 0;
                for(i=0;i<6;i++)
                    s->block_last_index[i] = -1;
                s->mv_dir = MV_DIR_FORWARD;
                s->mv_type = MV_TYPE_16X16;
                s->mv[0][0][0] = 0;
                s->mv[0][0][1] = 0;
                s->mb_skipped = 1;
                return 0;
            }
        }

        if(s->msmpeg4_version==2)
            code = get_vlc2(&s->gb, v2_mb_type_vlc.table, V2_MB_TYPE_VLC_BITS, 1);
        else
            code = get_vlc2(&s->gb, v1_inter_cbpc_vlc.table, V1_INTER_CBPC_VLC_BITS, 3);
        if(code<0 || code>7){
            av_log(s->avctx, AV_LOG_ERROR, "cbpc %d invalid at %d %d\n", code, s->mb_x, s->mb_y);
            return -1;
        }

        s->mb_intra = code >>2;

        cbp = code & 0x3;
    } else {
        s->mb_intra = 1;
        if(s->msmpeg4_version==2)
            cbp= get_vlc2(&s->gb, v2_intra_cbpc_vlc.table, V2_INTRA_CBPC_VLC_BITS, 1);
        else
            cbp= get_vlc2(&s->gb, v1_intra_cbpc_vlc.table, V1_INTRA_CBPC_VLC_BITS, 1);
        if(cbp<0 || cbp>3){
            av_log(s->avctx, AV_LOG_ERROR, "cbpc %d invalid at %d %d\n", cbp, s->mb_x, s->mb_y);
            return -1;
        }
    }

    if (!s->mb_intra) {
        int mx, my, cbpy;

        cbpy= get_vlc2(&s->gb, cbpy_vlc.table, CBPY_VLC_BITS, 1);
        if(cbpy<0){
            av_log(s->avctx, AV_LOG_ERROR, "cbpy %d invalid at %d %d\n", cbp, s->mb_x, s->mb_y);
            return -1;
        }

        cbp|= cbpy<<2;
        if(s->msmpeg4_version==1 || (cbp&3) != 3) cbp^= 0x3C;

        h263_pred_motion(s, 0, 0, &mx, &my);
        mx= msmpeg4v2_decode_motion(s, mx, 1);
        my= msmpeg4v2_decode_motion(s, my, 1);

        s->mv_dir = MV_DIR_FORWARD;
        s->mv_type = MV_TYPE_16X16;
        s->mv[0][0][0] = mx;
        s->mv[0][0][1] = my;
    } else {
        if(s->msmpeg4_version==2){
            s->ac_pred = get_bits1(&s->gb);
            cbp|= get_vlc2(&s->gb, cbpy_vlc.table, CBPY_VLC_BITS, 1)<<2; //FIXME check errors
        } else{
            s->ac_pred = 0;
            cbp|= get_vlc2(&s->gb, cbpy_vlc.table, CBPY_VLC_BITS, 1)<<2; //FIXME check errors
            if(s->pict_type==P_TYPE) cbp^=0x3C;
        }
    }

    s->dsp.clear_blocks(s->block[0]);
    for (i = 0; i < 6; i++) {
        if (msmpeg4_decode_block(s, block[i], i, (cbp >> (5 - i)) & 1, NULL) < 0)
        {
             av_log(s->avctx, AV_LOG_ERROR, "\nerror while decoding block: %d x %d (%d)\n", s->mb_x, s->mb_y, i);
             return -1;
        }
    }
    return 0;
}

static int msmpeg4v34_decode_mb(MpegEncContext *s, DCTELEM block[6][64])
{
    int cbp, code, i;
    uint8_t *coded_val;
    uint32_t * const mb_type_ptr= &s->current_picture.mb_type[ s->mb_x + s->mb_y*s->mb_stride ];

    if (s->pict_type == P_TYPE) {
        if (s->use_skip_mb_code) {
            if (get_bits1(&s->gb)) {
                /* skip mb */
                s->mb_intra = 0;
                for(i=0;i<6;i++)
                    s->block_last_index[i] = -1;
                s->mv_dir = MV_DIR_FORWARD;
                s->mv_type = MV_TYPE_16X16;
                s->mv[0][0][0] = 0;
                s->mv[0][0][1] = 0;
                s->mb_skipped = 1;
                *mb_type_ptr = MB_TYPE_SKIP | MB_TYPE_L0 | MB_TYPE_16x16;

                return 0;
            }
        }

        code = get_vlc2(&s->gb, mb_non_intra_vlc[DEFAULT_INTER_INDEX].table, MB_NON_INTRA_VLC_BITS, 3);
        if (code < 0)
            return -1;
        //s->mb_intra = (code & 0x40) ? 0 : 1;
        s->mb_intra = (~code & 0x40) >> 6;

        cbp = code & 0x3f;
    } else {
        s->mb_intra = 1;
        code = get_vlc2(&s->gb, ff_msmp4_mb_i_vlc.table, MB_INTRA_VLC_BITS, 2);
        if (code < 0)
            return -1;
        /* predict coded block pattern */
        cbp = 0;
        for(i=0;i<6;i++) {
            int val = ((code >> (5 - i)) & 1);
            if (i < 4) {
                int pred = coded_block_pred(s, i, &coded_val);
                val = val ^ pred;
                *coded_val = val;
            }
            cbp |= val << (5 - i);
        }
    }