mpeg12.c

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                }
                i += run;
                j = scantable[i];
                if(level<0){
                    level= -level;
                    level= ((level*2+1)*qscale*quant_matrix[j])>>4;
                    level= (level-1)|1;
                    level= -level;
                }else{
                    level= ((level*2+1)*qscale*quant_matrix[j])>>4;
                    level= (level-1)|1;
                }
            }
            if (i > 63){
                av_log(s->avctx, AV_LOG_ERROR, "ac-tex damaged at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }

            block[j] = level;
        }
        CLOSE_READER(re, &s->gb);
    }
    s->block_last_index[n] = i;
    return 0;
}

/* Also does unquantization here, since I will never support mpeg2
   encoding */
static inline int mpeg2_decode_block_non_intra(MpegEncContext *s, 
                               DCTELEM *block, 
                               int n)
{
    int level, i, j, run;
    RLTable *rl = &rl_mpeg1;
    uint8_t * const scantable= s->intra_scantable.permutated;
    const uint16_t *quant_matrix;
    const int qscale= s->qscale;
    int mismatch;

    mismatch = 1;

    {
        int v;
        OPEN_READER(re, &s->gb);
        i = -1;
        if (n < 4)
            quant_matrix = s->inter_matrix;
        else
            quant_matrix = s->chroma_inter_matrix;

        /* special case for the first coef. no need to add a second vlc table */
        UPDATE_CACHE(re, &s->gb);
        v= SHOW_UBITS(re, &s->gb, 2);
        if (v & 2) {
            LAST_SKIP_BITS(re, &s->gb, 2);
            level= (3*qscale*quant_matrix[0])>>5;
            if(v&1)
                level= -level;
            block[0] = level;
            mismatch ^= level;
            i++;
        }

        /* now quantify & encode AC coefs */
        for(;;) {
            UPDATE_CACHE(re, &s->gb);
            GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2);
            
            if(level == 127){
                break;
            } else if(level != 0) {
                i += run;
                j = scantable[i];
                level= ((level*2+1)*qscale*quant_matrix[j])>>5;
                level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
                LAST_SKIP_BITS(re, &s->gb, 1);
            } else {
                /* escape */
                run = SHOW_UBITS(re, &s->gb, 6)+1; LAST_SKIP_BITS(re, &s->gb, 6);
                UPDATE_CACHE(re, &s->gb);
                level = SHOW_SBITS(re, &s->gb, 12); SKIP_BITS(re, &s->gb, 12);

                i += run;
                j = scantable[i];
                if(level<0){
                    level= ((-level*2+1)*qscale*quant_matrix[j])>>5;
                    level= -level;
                }else{
                    level= ((level*2+1)*qscale*quant_matrix[j])>>5;
                }
            }
            if (i > 63){
                av_log(s->avctx, AV_LOG_ERROR, "ac-tex damaged at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }
            
            mismatch ^= level;
            block[j] = level;
        }
        CLOSE_READER(re, &s->gb);
    }
    block[63] ^= (mismatch & 1);
    
    s->block_last_index[n] = i;
    return 0;
}

static inline int mpeg2_decode_block_intra(MpegEncContext *s, 
                               DCTELEM *block, 
                               int n)
{
    int level, dc, diff, i, j, run;
    int component;
    RLTable *rl;
    uint8_t * const scantable= s->intra_scantable.permutated;
    const uint16_t *quant_matrix;
    const int qscale= s->qscale;
    int mismatch;

    /* DC coef */
    if (n < 4){
        quant_matrix = s->intra_matrix;
        component = 0; 
    }else{
        quant_matrix = s->chroma_intra_matrix;
        component = n - 3;
    }
    diff = decode_dc(&s->gb, component);
    if (diff >= 0xffff)
        return -1;
    dc = s->last_dc[component];
    dc += diff;
    s->last_dc[component] = dc;
    block[0] = dc << (3 - s->intra_dc_precision);
    dprintf("dc=%d\n", block[0]);
    mismatch = block[0] ^ 1;
    i = 0;
    if (s->intra_vlc_format)
        rl = &rl_mpeg2;
    else
        rl = &rl_mpeg1;

    {
        OPEN_READER(re, &s->gb);    
        /* now quantify & encode AC coefs */
        for(;;) {
            UPDATE_CACHE(re, &s->gb);
            GET_RL_VLC(level, run, re, &s->gb, rl->rl_vlc[0], TEX_VLC_BITS, 2);
            
            if(level == 127){
                break;
            } else if(level != 0) {
                i += run;
                j = scantable[i];
                level= (level*qscale*quant_matrix[j])>>4;
                level = (level ^ SHOW_SBITS(re, &s->gb, 1)) - SHOW_SBITS(re, &s->gb, 1);
                LAST_SKIP_BITS(re, &s->gb, 1);
            } else {
                /* escape */
                run = SHOW_UBITS(re, &s->gb, 6)+1; LAST_SKIP_BITS(re, &s->gb, 6);
                UPDATE_CACHE(re, &s->gb);
                level = SHOW_SBITS(re, &s->gb, 12); SKIP_BITS(re, &s->gb, 12);
                i += run;
                j = scantable[i];
                if(level<0){
                    level= (-level*qscale*quant_matrix[j])>>4;
                    level= -level;
                }else{
                    level= (level*qscale*quant_matrix[j])>>4;
                }
            }
            if (i > 63){
                av_log(s->avctx, AV_LOG_ERROR, "ac-tex damaged at %d %d\n", s->mb_x, s->mb_y);
                return -1;
            }
            
            mismatch^= level;
            block[j] = level;
        }
        CLOSE_READER(re, &s->gb);
    }
    block[63]^= mismatch&1;
    
    s->block_last_index[n] = i;
    return 0;
}

typedef struct Mpeg1Context {
    MpegEncContext mpeg_enc_ctx;
    int mpeg_enc_ctx_allocated; /* true if decoding context allocated */
    int repeat_field; /* true if we must repeat the field */
    AVPanScan pan_scan; /** some temporary storage for the panscan */
} Mpeg1Context;

static int mpeg_decode_init(AVCodecContext *avctx)
{
    Mpeg1Context *s = avctx->priv_data;
    
    s->mpeg_enc_ctx.flags= avctx->flags;
    common_init(&s->mpeg_enc_ctx);
    init_vlcs();

    s->mpeg_enc_ctx_allocated = 0;
    s->mpeg_enc_ctx.picture_number = 0;
    s->repeat_field = 0;
    s->mpeg_enc_ctx.codec_id= avctx->codec->id;
    return 0;
}

/* return the 8 bit start code value and update the search
   state. Return -1 if no start code found */
static int find_start_code(uint8_t **pbuf_ptr, uint8_t *buf_end)
{
    uint8_t *buf_ptr;
    unsigned int state=0xFFFFFFFF, v;
    int val;

    buf_ptr = *pbuf_ptr;
    while (buf_ptr < buf_end) {
        v = *buf_ptr++;
        if (state == 0x000001) {
            state = ((state << 8) | v) & 0xffffff;
            val = state;
            goto found;
        }
        state = ((state << 8) | v) & 0xffffff;
    }
    val = -1;
 found:
    *pbuf_ptr = buf_ptr;
    return val;
}

static int mpeg1_decode_picture(AVCodecContext *avctx, 
                                uint8_t *buf, int buf_size)
{
    Mpeg1Context *s1 = avctx->priv_data;
    MpegEncContext *s = &s1->mpeg_enc_ctx;
    int ref, f_code;

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

    ref = get_bits(&s->gb, 10); /* temporal ref */
    s->pict_type = get_bits(&s->gb, 3);
    dprintf("pict_type=%d number=%d\n", s->pict_type, s->picture_number);

    skip_bits(&s->gb, 16);
    if (s->pict_type == P_TYPE || s->pict_type == B_TYPE) {
        s->full_pel[0] = get_bits1(&s->gb);
        f_code = get_bits(&s->gb, 3);
        if (f_code == 0)
            return -1;
        s->mpeg_f_code[0][0] = f_code;
        s->mpeg_f_code[0][1] = f_code;
    }
    if (s->pict_type == B_TYPE) {
        s->full_pel[1] = get_bits1(&s->gb);
        f_code = get_bits(&s->gb, 3);
        if (f_code == 0)
            return -1;
        s->mpeg_f_code[1][0] = f_code;
        s->mpeg_f_code[1][1] = f_code;
    }
    s->current_picture.pict_type= s->pict_type;
    s->current_picture.key_frame= s->pict_type == I_TYPE;
    
    s->y_dc_scale = 8;
    s->c_dc_scale = 8;
    s->first_slice = 1;
    return 0;
}

static void mpeg_decode_sequence_extension(MpegEncContext *s)
{
    int horiz_size_ext, vert_size_ext;
    int bit_rate_ext, vbv_buf_ext;
    int frame_rate_ext_n, frame_rate_ext_d;
    int level, profile;

    skip_bits(&s->gb, 1); /* profil and level esc*/
    profile= get_bits(&s->gb, 3);
    level= get_bits(&s->gb, 4);
    s->progressive_sequence = get_bits1(&s->gb); /* progressive_sequence */
    skip_bits(&s->gb, 2); /* chroma_format */
    horiz_size_ext = get_bits(&s->gb, 2);
    vert_size_ext = get_bits(&s->gb, 2);
    s->width |= (horiz_size_ext << 12);
    s->height |= (vert_size_ext << 12);
    bit_rate_ext = get_bits(&s->gb, 12);  /* XXX: handle it */
    s->bit_rate = ((s->bit_rate / 400) | (bit_rate_ext << 12)) * 400;
    skip_bits1(&s->gb); /* marker */
    vbv_buf_ext = get_bits(&s->gb, 8);

    s->low_delay = get_bits1(&s->gb);
    if(s->flags & CODEC_FLAG_LOW_DELAY) s->low_delay=1;

    frame_rate_ext_n = get_bits(&s->gb, 2);
    frame_rate_ext_d = get_bits(&s->gb, 5);
    av_reduce(
        &s->avctx->frame_rate, 
        &s->avctx->frame_rate_base, 
        frame_rate_tab[s->frame_rate_index] * (frame_rate_ext_n+1),
        MPEG1_FRAME_RATE_BASE * (frame_rate_ext_d+1),
        1<<30);

    dprintf("sequence extension\n");
    s->codec_id= s->avctx->codec_id= CODEC_ID_MPEG2VIDEO;
    s->avctx->sub_id = 2; /* indicates mpeg2 found */

    if(s->aspect_ratio_info <= 1)
        s->avctx->sample_aspect_ratio= mpeg2_aspect[s->aspect_ratio_info];
    else{
        s->avctx->sample_aspect_ratio= 
            av_div_q(
                mpeg2_aspect[s->aspect_ratio_info], 
                (AVRational){s->width, s->height}
            );
    }
    
    if(s->avctx->debug & FF_DEBUG_PICT_INFO)
        av_log(s->avctx, AV_LOG_DEBUG, "profile: %d, level: %d \n", profile, level);
}

static void mpeg_decode_sequence_display_extension(Mpeg1Context *s1)
{
    MpegEncContext *s= &s1->mpeg_enc_ctx;
    int color_description, w, h;

    skip_bits(&s->gb, 3); /* video format */
    color_description= get_bits1(&s->gb);
    if(color_description){
        skip_bits(&s->gb, 8); /* color primaries */
        skip_bits(&s->gb, 8); /* transfer_characteristics */
        skip_bits(&s->gb, 8); /* matrix_coefficients */
    }
    w= get_bits(&s->gb, 14);
    skip_bits(&s->gb, 1); //marker
    h= get_bits(&s->gb, 14);
    skip_bits(&s->gb, 1); //marker
    
    s1->pan_scan.width= 16*w;
    s1->pan_scan.height=16*h;

    if(s->aspect_ratio_info > 1)
        s->avctx->sample_aspect_ratio= 
            av_div_q(
                mpeg2_aspect[s->aspect_ratio_info], 
                (AVRational){w, h}
            );
    
    if(s->avctx->debug & FF_DEBUG_PICT_INFO)
        av_log(s->avctx, AV_LOG_DEBUG, "sde w:%d, h:%d\n", w, h);
}

static void mpeg_decode_picture_display_extension(Mpeg1Context *s1)
{
    MpegEncContext *s= &s1->mpeg_enc_ctx;
    int i;

    for(i=0; i<1; i++){ //FIXME count
        s1->pan_scan.position[i][0]= get_sbits(&s->gb, 16);
        skip_bits(&s->gb, 1); //marker
        s1->pan_scan.position[i][1]= get_sbits(&s->gb, 16);
        skip_bits(&s->gb, 1); //marker
    }
   
    if(s->avctx->debug & FF_DEBUG_PICT_INFO)
        av_log(s->avctx, AV_LOG_DEBUG, "pde (%d,%d) (%d,%d) (%d,%d)\n", 
            s1->pan_scan.position[0][0], s1->pan_scan.position[0][1], 
            s1->pan_scan.position[1][0], s1->pan_scan.position[1][1], 
            s1->pan_scan.position[2][0], s1->pan_scan.position[2][1]