4xm.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

        val = get_xbits(&f->gb, val);

    val = val * dequant_table[0] + f->last_dc;
    f->last_dc =
    block[0] = val;
    /* AC coefs */
    i = 1;
    for(;;) {
        code = get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3);

        /* EOB */
        if (code == 0)
            break;
        if (code == 0xf0) {
            i += 16;
        } else {
            level = get_xbits(&f->gb, code & 0xf);
            i += code >> 4;
            if (i >= 64) {
                av_log(f->avctx, AV_LOG_ERROR, "run %d oveflow\n", i);
                return 0;
            }

            j= ff_zigzag_direct[i];
            block[j] = level * dequant_table[j];
            i++;
            if (i >= 64)
                break;
        }
    }

    return 0;
}

static inline void idct_put(FourXContext *f, int x, int y){
    DCTELEM (*block)[64]= f->block;
    int stride= f->current_picture.linesize[0]>>1;
    int i;
    uint16_t *dst = ((uint16_t*)f->current_picture.data[0]) + y * stride + x;

    for(i=0; i<4; i++){
        block[i][0] += 0x80*8*8;
        idct(block[i]);
    }

    if(!(f->avctx->flags&CODEC_FLAG_GRAY)){
        for(i=4; i<6; i++) idct(block[i]);
    }

/* Note transform is:
y= ( 1b + 4g + 2r)/14
cb=( 3b - 2g - 1r)/14
cr=(-1b - 4g + 5r)/14
*/
    for(y=0; y<8; y++){
        for(x=0; x<8; x++){
            DCTELEM *temp= block[(x>>2) + 2*(y>>2)] + 2*(x&3) + 2*8*(y&3); //FIXME optimize
            int cb= block[4][x + 8*y];
            int cr= block[5][x + 8*y];
            int cg= (cb + cr)>>1;
            int y;

            cb+=cb;

            y = temp[0];
            dst[0       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
            y = temp[1];
            dst[1       ]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
            y = temp[8];
            dst[  stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
            y = temp[9];
            dst[1+stride]= ((y+cb)>>3) + (((y-cg)&0xFC)<<3) + (((y+cr)&0xF8)<<8);
            dst += 2;
        }
        dst += 2*stride - 2*8;
    }
}

static int decode_i_mb(FourXContext *f){
    int i;

    f->dsp.clear_blocks(f->block[0]);

    for(i=0; i<6; i++){
        if(decode_i_block(f, f->block[i]) < 0)
            return -1;
    }

    return 0;
}

static uint8_t *read_huffman_tables(FourXContext *f, uint8_t * const buf){
    int frequency[512];
    uint8_t flag[512];
    int up[512];
    uint8_t len_tab[257];
    int bits_tab[257];
    int start, end;
    uint8_t *ptr= buf;
    int j;

    memset(frequency, 0, sizeof(frequency));
    memset(up, -1, sizeof(up));

    start= *ptr++;
    end= *ptr++;
    for(;;){
        int i;

        for(i=start; i<=end; i++){
            frequency[i]= *ptr++;
        }
        start= *ptr++;
        if(start==0) break;

        end= *ptr++;
    }
    frequency[256]=1;

    while((ptr - buf)&3) ptr++; // 4byte align

    for(j=257; j<512; j++){
        int min_freq[2]= {256*256, 256*256};
        int smallest[2]= {0, 0};
        int i;
        for(i=0; i<j; i++){
            if(frequency[i] == 0) continue;
            if(frequency[i] < min_freq[1]){
                if(frequency[i] < min_freq[0]){
                    min_freq[1]= min_freq[0]; smallest[1]= smallest[0];
                    min_freq[0]= frequency[i];smallest[0]= i;
                }else{
                    min_freq[1]= frequency[i];smallest[1]= i;
                }
            }
        }
        if(min_freq[1] == 256*256) break;

        frequency[j]= min_freq[0] + min_freq[1];
        flag[ smallest[0] ]= 0;
        flag[ smallest[1] ]= 1;
        up[ smallest[0] ]=
        up[ smallest[1] ]= j;
        frequency[ smallest[0] ]= frequency[ smallest[1] ]= 0;
    }

    for(j=0; j<257; j++){
        int node;
        int len=0;
        int bits=0;

        for(node= j; up[node] != -1; node= up[node]){
            bits += flag[node]<<len;
            len++;
            if(len > 31) av_log(f->avctx, AV_LOG_ERROR, "vlc length overflow\n"); //can this happen at all ?
        }

        bits_tab[j]= bits;
        len_tab[j]= len;
    }

    init_vlc(&f->pre_vlc, ACDC_VLC_BITS, 257,
             len_tab , 1, 1,
             bits_tab, 4, 4, 0);

    return ptr;
}

static int mix(int c0, int c1){
    int blue = 2*(c0&0x001F) + (c1&0x001F);
    int green= (2*(c0&0x03E0) + (c1&0x03E0))>>5;
    int red  = 2*(c0>>10) + (c1>>10);
    return red/3*1024 + green/3*32 + blue/3;
}

static int decode_i2_frame(FourXContext *f, uint8_t *buf, int length){
    int x, y, x2, y2;
    const int width= f->avctx->width;
    const int height= f->avctx->height;
    uint16_t *dst= (uint16_t*)f->current_picture.data[0];
    const int stride= f->current_picture.linesize[0]>>1;

    for(y=0; y<height; y+=16){
        for(x=0; x<width; x+=16){
            unsigned int color[4], bits;
            memset(color, 0, sizeof(color));
//warning following is purely guessed ...
            color[0]= bytestream_get_le16(&buf);
            color[1]= bytestream_get_le16(&buf);

            if(color[0]&0x8000) av_log(NULL, AV_LOG_ERROR, "unk bit 1\n");
            if(color[1]&0x8000) av_log(NULL, AV_LOG_ERROR, "unk bit 2\n");

            color[2]= mix(color[0], color[1]);
            color[3]= mix(color[1], color[0]);

            bits= bytestream_get_le32(&buf);
            for(y2=0; y2<16; y2++){
                for(x2=0; x2<16; x2++){
                    int index= 2*(x2>>2) + 8*(y2>>2);
                    dst[y2*stride+x2]= color[(bits>>index)&3];
                }
            }
            dst+=16;
        }
        dst += 16*stride - width;
    }

    return 0;
}

static int decode_i_frame(FourXContext *f, uint8_t *buf, int length){
    int x, y;
    const int width= f->avctx->width;
    const int height= f->avctx->height;
    uint16_t *dst= (uint16_t*)f->current_picture.data[0];
    const int stride= f->current_picture.linesize[0]>>1;
    const unsigned int bitstream_size= get32(buf);
    const int token_count av_unused = get32(buf + bitstream_size + 8);
    unsigned int prestream_size= 4*get32(buf + bitstream_size + 4);
    uint8_t *prestream= buf + bitstream_size + 12;

    if(prestream_size + bitstream_size + 12 != length
       || bitstream_size > (1<<26)
       || prestream_size > (1<<26)){
        av_log(f->avctx, AV_LOG_ERROR, "size mismatch %d %d %d\n", prestream_size, bitstream_size, length);
        return -1;
    }

    prestream= read_huffman_tables(f, prestream);

    init_get_bits(&f->gb, buf + 4, 8*bitstream_size);

    prestream_size= length + buf - prestream;

    f->bitstream_buffer= av_fast_realloc(f->bitstream_buffer, &f->bitstream_buffer_size, prestream_size + FF_INPUT_BUFFER_PADDING_SIZE);
    f->dsp.bswap_buf((uint32_t*)f->bitstream_buffer, (uint32_t*)prestream, prestream_size/4);
    init_get_bits(&f->pre_gb, f->bitstream_buffer, 8*prestream_size);

    f->last_dc= 0*128*8*8;

    for(y=0; y<height; y+=16){
        for(x=0; x<width; x+=16){
            if(decode_i_mb(f) < 0)
                return -1;

            idct_put(f, x, y);
        }
        dst += 16*stride;
    }

    if(get_vlc2(&f->pre_gb, f->pre_vlc.table, ACDC_VLC_BITS, 3) != 256)
        av_log(f->avctx, AV_LOG_ERROR, "end mismatch\n");

    return 0;
}

static int decode_frame(AVCodecContext *avctx,
                        void *data, int *data_size,
                        uint8_t *buf, int buf_size)
{
    FourXContext * const f = avctx->priv_data;
    AVFrame *picture = data;
    AVFrame *p, temp;
    int i, frame_4cc, frame_size;

    frame_4cc= get32(buf);
    if(buf_size != get32(buf+4)+8 || buf_size < 20){
        av_log(f->avctx, AV_LOG_ERROR, "size mismatch %d %d\n", buf_size, get32(buf+4));
    }

    if(frame_4cc == ff_get_fourcc("cfrm")){
        int free_index=-1;
        const int data_size= buf_size - 20;
        const int id= get32(buf+12);
        const int whole_size= get32(buf+16);
        CFrameBuffer *cfrm;

        for(i=0; i<CFRAME_BUFFER_COUNT; i++){
            if(f->cfrm[i].id && f->cfrm[i].id < avctx->frame_number)
                av_log(f->avctx, AV_LOG_ERROR, "lost c frame %d\n", f->cfrm[i].id);
        }

        for(i=0; i<CFRAME_BUFFER_COUNT; i++){
            if(f->cfrm[i].id   == id) break;
            if(f->cfrm[i].size == 0 ) free_index= i;
        }

        if(i>=CFRAME_BUFFER_COUNT){
            i= free_index;
            f->cfrm[i].id= id;
        }
        cfrm= &f->cfrm[i];

        cfrm->data= av_fast_realloc(cfrm->data, &cfrm->allocated_size, cfrm->size + data_size + FF_INPUT_BUFFER_PADDING_SIZE);
        if(!cfrm->data){ //explicit check needed as memcpy below might not catch a NULL
            av_log(f->avctx, AV_LOG_ERROR, "realloc falure");
            return -1;
        }

        memcpy(cfrm->data + cfrm->size, buf+20, data_size);
        cfrm->size += data_size;

        if(cfrm->size >= whole_size){
            buf= cfrm->data;
            frame_size= cfrm->size;

            if(id != avctx->frame_number){
                av_log(f->avctx, AV_LOG_ERROR, "cframe id mismatch %d %d\n", id, avctx->frame_number);
            }

            cfrm->size= cfrm->id= 0;
            frame_4cc= ff_get_fourcc("pfrm");
        }else
            return buf_size;
    }else{
        buf= buf + 12;
        frame_size= buf_size - 12;
    }

    temp= f->current_picture;
    f->current_picture= f->last_picture;
    f->last_picture= temp;

    p= &f->current_picture;
    avctx->coded_frame= p;

    avctx->flags |= CODEC_FLAG_EMU_EDGE; // alternatively we would have to use our own buffer management

    if(p->data[0])
        avctx->release_buffer(avctx, p);

    p->reference= 1;
    if(avctx->get_buffer(avctx, p) < 0){
        av_log(avctx, AV_LOG_ERROR, "get_buffer() failed\n");
        return -1;
    }

    if(frame_4cc == ff_get_fourcc("ifr2")){
        p->pict_type= I_TYPE;
        if(decode_i2_frame(f, buf-4, frame_size) < 0)
            return -1;
    }else if(frame_4cc == ff_get_fourcc("ifrm")){
        p->pict_type= I_TYPE;
        if(decode_i_frame(f, buf, frame_size) < 0)
            return -1;
    }else if(frame_4cc == ff_get_fourcc("pfrm") || frame_4cc == ff_get_fourcc("pfr2")){
        p->pict_type= P_TYPE;
        if(decode_p_frame(f, buf, frame_size) < 0)
            return -1;
    }else if(frame_4cc == ff_get_fourcc("snd_")){
        av_log(avctx, AV_LOG_ERROR, "ignoring snd_ chunk length:%d\n", buf_size);
    }else{
        av_log(avctx, AV_LOG_ERROR, "ignoring unknown chunk length:%d\n", buf_size);
    }

    p->key_frame= p->pict_type == I_TYPE;

    *picture= *p;
    *data_size = sizeof(AVPicture);

    emms_c();

    return buf_size;
}


static void common_init(AVCodecContext *avctx){
    FourXContext * const f = avctx->priv_data;

    dsputil_init(&f->dsp, avctx);

    f->avctx= avctx;
}

static int decode_init(AVCodecContext *avctx){
    FourXContext * const f = avctx->priv_data;

    if(avctx->extradata_size != 4 || !avctx->extradata) {
        av_log(avctx, AV_LOG_ERROR, "extradata wrong or missing\n");
        return 1;
    }

    f->version= AV_RL32(avctx->extradata)>>16;
    common_init(avctx);
    init_vlcs(f);

    if(f->version>2) avctx->pix_fmt= PIX_FMT_RGB565;
    else             avctx->pix_fmt= PIX_FMT_RGB555;

    return 0;
}


static int decode_end(AVCodecContext *avctx){
    FourXContext * const f = avctx->priv_data;
    int i;

    av_freep(&f->bitstream_buffer);
    f->bitstream_buffer_size=0;
    for(i=0; i<CFRAME_BUFFER_COUNT; i++){
        av_freep(&f->cfrm[i].data);
        f->cfrm[i].allocated_size= 0;
    }
    free_vlc(&f->pre_vlc);

    return 0;
}

AVCodec fourxm_decoder = {
    "4xm",
    CODEC_TYPE_VIDEO,
    CODEC_ID_4XM,
    sizeof(FourXContext),
    decode_init,
    NULL,
    decode_end,
    decode_frame,
    /*CODEC_CAP_DR1,*/
};