h261.c

FFmpeg is an audio/video conversion tool. It includes libavcodec, the leading open source codec libr

    if(!coded){
        s->block_last_index[n] = i - 1;
        return 0;
    }
    for(;;){
        code = get_vlc2(&s->gb, rl->vlc.table, TCOEFF_VLC_BITS, 2);
        if (code < 0){
            av_log(s->avctx, AV_LOG_ERROR, "illegal ac vlc code at %dx%d\n", s->mb_x, s->mb_y);
            return -1;
        }
        if (code == rl->n) {
            /* escape */
            // The remaining combinations of (run, level) are encoded with a 20-bit word consisting of 6 bits escape, 6 bits run and 8 bits level.
            run = get_bits(&s->gb, 6);
            level = (int8_t)get_bits(&s->gb, 8);
        }else if(code == 0){
            break;
        }else{
            run = rl->table_run[code];
            level = rl->table_level[code];
            if (get_bits1(&s->gb))
                level = -level;
        }
        i += run;
        if (i >= 64){
            av_log(s->avctx, AV_LOG_ERROR, "run overflow at %dx%d\n", s->mb_x, s->mb_y);
            return -1;
        }
        j = scan_table[i];
        block[j] = level;
        i++;
    }
    s->block_last_index[n] = i;
    return 0;
}

/**
 * decodes the H261 picture header.
 * @return <0 if no startcode found
 */
int h261_decode_picture_header(H261Context *h){
    MpegEncContext * const s = &h->s;
    int format, i;
    static int h261_framecounter = 0;
    uint32_t startcode;
    align_get_bits(&s->gb);

    startcode = (h->last_bits << (12 - (8-h->bits_left))) | get_bits(&s->gb, 20-8 - (8- h->bits_left));

    for(i= s->gb.size_in_bits - get_bits_count(&s->gb); i>24; i-=1){
        startcode = ((startcode << 1) | get_bits(&s->gb, 1)) & 0x000FFFFF;

        if(startcode == 0x10)
            break;
    }

    if (startcode != 0x10){
        av_log(s->avctx, AV_LOG_ERROR, "Bad picture start code\n");
        return -1;
    }

    /* temporal reference */
    s->picture_number = get_bits(&s->gb, 5); /* picture timestamp */

    /* PTYPE starts here */
    skip_bits1(&s->gb); /* split screen off */
    skip_bits1(&s->gb); /* camera  off */
    skip_bits1(&s->gb); /* freeze picture release off */

    format = get_bits1(&s->gb);

    //only 2 formats possible
    if (format == 0){//QCIF
        s->width = 176;
        s->height = 144;
        s->mb_width = 11;
        s->mb_height = 9;
    }else{//CIF
        s->width = 352;
        s->height = 288;
        s->mb_width = 22;
        s->mb_height = 18;
    }

    s->mb_num = s->mb_width * s->mb_height;

    skip_bits1(&s->gb); /* still image mode off */
    skip_bits1(&s->gb); /* Reserved */

    /* PEI */
    while (get_bits1(&s->gb) != 0){
        skip_bits(&s->gb, 8);
    }

    //h261 has no I-FRAMES, pass the test in MPV_frame_start in mpegvideo.c
    if(h261_framecounter > 1)
        s->pict_type = P_TYPE;
    else
        s->pict_type = I_TYPE;

    h261_framecounter++;

    h->gob_number = 0;
    return 0;
}

static int h261_decode_gob(H261Context *h){
    MpegEncContext * const s = &h->s;
    int i;
    
    ff_set_qscale(s, s->qscale);
    while(h->current_mba <= MAX_MBA)
    {
        int ret;
        /* DCT & quantize */
        s->dsp.clear_blocks(s->block[0]);
        ret= h261_decode_mb(h, s->block);
        if(ret<0){
            const int xy= s->mb_x + s->mb_y*s->mb_stride;
            if(ret==SLICE_END){
                MPV_decode_mb(s, s->block);
                if(h->loop_filter){
                    ff_h261_loop_filter(h);
                }
                h->loop_filter = 0;
                for(i=1; i<h->mba_diff; i++){
                    s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1-i) % 11);
                    s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1-i) / 11);
                    ff_init_block_index(s);
                    ff_update_block_index(s);
                    s->dsp.clear_blocks(s->block[0]);
                    ret= h261_decode_mb_skipped(h, s->block);
                    MPV_decode_mb(s, s->block);
                }
                
                return 0;
            }else if(ret==SLICE_NOEND){
                av_log(s->avctx, AV_LOG_ERROR, "Slice mismatch at MB: %d\n", xy);
                return -1;
            }
            av_log(s->avctx, AV_LOG_ERROR, "Error at MB: %d\n", xy);
            return -1;
        }
        MPV_decode_mb(s, s->block);
        if(h->loop_filter){
            ff_h261_loop_filter(h);
        }

        h->loop_filter = 0;
        for(i=1; i<h->mba_diff; i++){
            s->mb_x= ((h->gob_number-1) % 2) * 11 + ((h->current_mba-1-i) % 11);
            s->mb_y= ((h->gob_number-1) / 2) * 3 + ((h->current_mba-1-i) / 11);
            ff_init_block_index(s);
            ff_update_block_index(s);
            s->dsp.clear_blocks(s->block[0]);
            ret= h261_decode_mb_skipped(h, s->block);
            MPV_decode_mb(s, s->block);
        }
    }
    
    return -1;
}

static int h261_find_frame_end(ParseContext *pc, AVCodecContext* avctx, const uint8_t *buf, int buf_size){
    int vop_found, i, j, bits_left, last_bits;
    uint32_t state;

    H261Context *h = avctx->priv_data;

    if(h){
        bits_left = h->bits_left;
        last_bits = h->last_bits;
    }
    else{
        bits_left = 0;
        last_bits = 0;
    }

    vop_found= pc->frame_start_found;
    state= pc->state;
    if(bits_left!=0 && !vop_found)
        state = state << (8-bits_left) | last_bits;
    i=0;
    if(!vop_found){
        for(i=0; i<buf_size; i++){
            state= (state<<8) | buf[i];
            for(j=0; j<8; j++){
                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
                    i++;
                    vop_found=1;
                    break;
                }
            }
            if(vop_found)
                    break;    
        }
    }
    if(vop_found){
        for(; i<buf_size; i++){
            if(avctx->flags & CODEC_FLAG_TRUNCATED)//XXX ffplay workaround, someone a better solution?
                state= (state<<8) | buf[i];
            for(j=0; j<8; j++){
                if(( (  (state<<j)  |  (buf[i]>>(8-j))  )>>(32-20) == 0x10 )&&(((state >> (17-j)) & 0x4000) == 0x0)){
                    pc->frame_start_found=0;
                    pc->state=-1;
                    return i-3;
                }
            }
        }
    }

    pc->frame_start_found= vop_found;
    pc->state= state;
    return END_NOT_FOUND;
}

static int h261_parse(AVCodecParserContext *s,
                      AVCodecContext *avctx,
                      uint8_t **poutbuf, int *poutbuf_size, 
                      const uint8_t *buf, int buf_size)
{
    ParseContext *pc = s->priv_data;
    int next;
    
    next= h261_find_frame_end(pc,avctx, buf, buf_size);
    if (ff_combine_frame(pc, next, (uint8_t **)&buf, &buf_size) < 0) {
        *poutbuf = NULL;
        *poutbuf_size = 0;
        return buf_size;
    }
    *poutbuf = (uint8_t *)buf;
    *poutbuf_size = buf_size;
    return next;
}

/**
 * returns the number of bytes consumed for building the current frame
 */
static int get_consumed_bytes(MpegEncContext *s, int buf_size){
    int pos= (get_bits_count(&s->gb)+7)>>3;

    if(s->flags&CODEC_FLAG_TRUNCATED){
        pos -= s->parse_context.last_index;
        if(pos<0) pos=0;// padding is not really read so this might be -1
        return pos;
    }else{
        if(pos==0) pos=1; //avoid infinite loops (i doubt thats needed but ...)
        if(pos+10>buf_size) pos=buf_size; // oops ;)

        return pos;
    }
}

static int h261_decode_frame(AVCodecContext *avctx,
                             void *data, int *data_size,
                             uint8_t *buf, int buf_size)
{
    H261Context *h= avctx->priv_data;
    MpegEncContext *s = &h->s;
    int ret;
    AVFrame *pict = data;

#ifdef DEBUG
    printf("*****frame %d size=%d\n", avctx->frame_number, buf_size);
    printf("bytes=%x %x %x %x\n", buf[0], buf[1], buf[2], buf[3]);
#endif
    s->flags= avctx->flags;
    s->flags2= avctx->flags2;

    /* no supplementary picture */
    if (buf_size == 0) {

        return 0;
    }

    if(s->flags&CODEC_FLAG_TRUNCATED){
        int next;

        next= h261_find_frame_end(&s->parse_context,avctx, buf, buf_size);

        if( ff_combine_frame(&s->parse_context, next, &buf, &buf_size) < 0 )
            return buf_size;
    }


retry:

    init_get_bits(&s->gb, buf, buf_size*8);

    if(!s->context_initialized){
        if (MPV_common_init(s) < 0) //we need the idct permutaton for reading a custom matrix
            return -1;
    }

    //we need to set current_picture_ptr before reading the header, otherwise we cant store anyting im there
    if(s->current_picture_ptr==NULL || s->current_picture_ptr->data[0]){
        int i= ff_find_unused_picture(s, 0);
        s->current_picture_ptr= &s->picture[i];
    }

    ret = h261_decode_picture_header(h);

    /* skip if the header was thrashed */
    if (ret < 0){
        av_log(s->avctx, AV_LOG_ERROR, "header damaged\n");
        return -1;
    }

    if (s->width != avctx->width || s->height != avctx->height){
        ParseContext pc= s->parse_context; //FIXME move these demuxng hack to avformat
        s->parse_context.buffer=0;
        MPV_common_end(s);
        s->parse_context= pc;
    }
    if (!s->context_initialized) {
        avctx->width = s->width;
        avctx->height = s->height;

        goto retry;
    }

    // for hurry_up==5
    s->current_picture.pict_type= s->pict_type;
    s->current_picture.key_frame= s->pict_type == I_TYPE;

    /* skip everything if we are in a hurry>=5 */
    if(avctx->hurry_up>=5) return get_consumed_bytes(s, buf_size);

    if(MPV_frame_start(s, avctx) < 0)
        return -1;

    ff_er_frame_start(s);

    /* decode each macroblock */
    s->mb_x=0;
    s->mb_y=0;

    while(h->gob_number < (s->mb_height==18 ? 12 : 5)){
        if(ff_h261_resync(h)<0)
            break;
        h261_decode_gob(h);
    }
    MPV_frame_end(s);

    // h261 doesn't have byte aligned codes
    // store the bits of the next frame that are left in the last byte
    // in the H261Context and remember the number of stored bits
    {
        int bitsleft;
        int current_pos= get_bits_count(&s->gb)>>3;
        bitsleft =  (current_pos<<3) - get_bits_count(&s->gb);
        h->bits_left = - bitsleft;
        if(bitsleft > 0)
            h->last_bits= get_bits(&s->gb, 8 - h->bits_left);
        else
            h->last_bits = 0;
    }

assert(s->current_picture.pict_type == s->current_picture_ptr->pict_type);
assert(s->current_picture.pict_type == s->pict_type);
    *pict= *(AVFrame*)&s->current_picture;
    ff_print_debug_info(s, pict);

    /* Return the Picture timestamp as the frame number */
    /* we substract 1 because it is added on utils.c    */
    avctx->frame_number = s->picture_number - 1;

    *data_size = sizeof(AVFrame);

    return get_consumed_bytes(s, buf_size);
}

static int h261_decode_end(AVCodecContext *avctx)
{
    H261Context *h= avctx->priv_data;
    MpegEncContext *s = &h->s;

    MPV_common_end(s);
    return 0;
}

AVCodec h261_decoder = {
    "h261",
    CODEC_TYPE_VIDEO,
    CODEC_ID_H261,
    sizeof(H261Context),
    h261_decode_init,
    NULL,
    h261_decode_end,
    h261_decode_frame,
    CODEC_CAP_TRUNCATED,
};

AVCodecParser h261_parser = {
    { CODEC_ID_H261 },
    sizeof(ParseContext),
    NULL,
    h261_parse,
    ff_parse_close,
};