h263enc.c

杜比AC-3编码解码器（参考程序）

        if (run < 2 && level < 4) {                             \
            len = coeff_tab2[run][level - 1][1];                \
            code = coeff_tab2[run][level - 1][0];               \
        } else if (run >= 2 && run < 42 && level == 1) {        \
            len = coeff_tab3[run - 2][1];                       \
            code = coeff_tab3[run - 2][0];                      \
        }                                                       \
    }                                                           \
}

static void h263_encode_block(MpegEncContext * s, DCTELEM * block, int n)
{
    int level, run, last, i, j, last_index, last_non_zero, sign, slevel;
    int code = 0, len;

    if (s->mb_intra) {
	/* DC coef */
	level = block[0];
	if (level == 128)
	    put_bits(&s->pb, 8, 0xff);
	else
	    put_bits(&s->pb, 8, level & 0xff);
	i = 1;
    } else {
	i = 0;
    }

    /* AC coefs */
    last_index = s->block_last_index[n];
    last_non_zero = i - 1;
    for (; i <= last_index; i++) {
	j = zigzag_direct[i];
	level = block[j];
	if (level) {
	    run = i - last_non_zero - 1;
	    last = (i == last_index);
	    sign = 0;
	    slevel = level;
	    if (level < 0) {
		sign = 1;
		level = -level;
	    }
            len = 0;
            CODE_INTER(run, level, last);
            if (len == 0) {
                put_bits(&s->pb, 7, 3);
                put_bits(&s->pb, 1, last);
                put_bits(&s->pb, 6, run);
                put_bits(&s->pb, 8, slevel & 0xff);
            } else {
                code = (code << 1) | sign;
                put_bits(&s->pb, len + 1, code);
            }
	    last_non_zero = i;
	}
    }
}

/* write RV 1.0 compatible frame header */
void rv10_encode_picture_header(MpegEncContext * s, int picture_number)
{
    align_put_bits(&s->pb);

    put_bits(&s->pb, 1, 1);	/* marker */

    put_bits(&s->pb, 1, (s->pict_type == P_TYPE));

    put_bits(&s->pb, 1, 0);	/* not PB frame */

    put_bits(&s->pb, 5, s->qscale);

    if (s->pict_type == I_TYPE) {
	/* specific MPEG like DC coding not used */
    }
    /* if multiple packets per frame are sent, the position at which
       to display the macro blocks is coded here */
    put_bits(&s->pb, 6, 0);	/* mb_x */
    put_bits(&s->pb, 6, 0);	/* mb_y */
    put_bits(&s->pb, 12, s->mb_width * s->mb_height);

    put_bits(&s->pb, 3, 0);	/* ignored */
}

/***************************************************/

/* write mpeg4 VOP header */
void mpeg4_encode_picture_header(MpegEncContext * s, int picture_number)
{
    align_put_bits(&s->pb);

    put_bits(&s->pb, 32, 0x1B6);	/* vop header */
    put_bits(&s->pb, 2, s->pict_type - 1);	/* pict type: I = 0 , P = 1 */
    /* XXX: time base + 1 not always correct */
    put_bits(&s->pb, 1, 1);
    put_bits(&s->pb, 1, 0);

    put_bits(&s->pb, 1, 1);	/* marker */
    put_bits(&s->pb, 4, 1);	/* XXX: correct time increment */
    put_bits(&s->pb, 1, 1);	/* marker */
    put_bits(&s->pb, 1, 1);	/* vop coded */
    if (s->pict_type == P_TYPE)
	put_bits(&s->pb, 1, 0);	/* rounding type */
    put_bits(&s->pb, 3, 0);	/* intra dc VLC threshold */

    put_bits(&s->pb, 5, s->qscale);

    if (s->pict_type != I_TYPE)
	put_bits(&s->pb, 3, s->f_code);	/* fcode_for */
}

void h263_dc_scale(MpegEncContext * s)
{
    int quant;

    quant = s->qscale;
    /* luminance */
    if (quant < 5)
	s->y_dc_scale = 8;
    else if (quant > 4 && quant < 9)
	s->y_dc_scale = (2 * quant);
    else if (quant > 8 && quant < 25)
	s->y_dc_scale = (quant + 8);
    else
	s->y_dc_scale = (2 * quant - 16);
    /* chrominance */
    if (quant < 5)
	s->c_dc_scale = 8;
    else if (quant > 4 && quant < 25)
	s->c_dc_scale = ((quant + 13) / 2);
    else
	s->c_dc_scale = (quant - 6);
}

static inline void mpeg4_encode_dc(MpegEncContext * s, int level, int n)
{
    int size, v, a, b, c, x, y, wrap, pred, scale;
    UINT16 *dc_val;

    /* find prediction */
    if (n < 4) {
	x = 2 * s->mb_x + 1 + (n & 1);
	y = 2 * s->mb_y + 1 + ((n & 2) >> 1);
	wrap = s->mb_width * 2 + 2;
	dc_val = s->dc_val[0];
	scale = s->y_dc_scale;
    } else {
	x = s->mb_x + 1;
	y = s->mb_y + 1;
	wrap = s->mb_width + 2;
	dc_val = s->dc_val[n - 4 + 1];
	scale = s->c_dc_scale;
    }

    /* B C
     * A X 
     */
    a = dc_val[(x - 1) + (y) * wrap];
    b = dc_val[(x - 1) + (y - 1) * wrap];
    c = dc_val[(x) + (y - 1) * wrap];

    if (abs(a - b) < abs(b - c)) {
	pred = c;
    } else {
	pred = a;
    }
    /* we assume pred is positive */
    pred = (pred + (scale >> 1)) / scale;

    /* update predictor */
    dc_val[(x) + (y) * wrap] = level * scale;

    /* do the prediction */
    level -= pred;

    /* find number of bits */
    size = 0;
    v = abs(level);
    while (v) {
	v >>= 1;
	size++;
    }

    if (n < 4) {
	/* luminance */
	put_bits(&s->pb, DCtab_lum[size][1], DCtab_lum[size][0]);
    } else {
	/* chrominance */
	put_bits(&s->pb, DCtab_chrom[size][1], DCtab_chrom[size][0]);
    }

    /* encode remaining bits */
    if (size > 0) {
	if (level < 0)
	    level = (-level) ^ ((1 << size) - 1);
	put_bits(&s->pb, size, level);
	if (size > 8)
	    put_bits(&s->pb, 1, 1);
    }
}

static void mpeg4_encode_block(MpegEncContext * s, DCTELEM * block, int n)
{
    int level, run, last, i, j, last_index, last_non_zero, sign, slevel, level1, run1;
    int code = 0, len;

    if (s->mb_intra) {
	/* mpeg4 based DC predictor */
	mpeg4_encode_dc(s, block[0], n);
	i = 1;
    } else {
	i = 0;
    }

    /* AC coefs */
    last_index = s->block_last_index[n];
    last_non_zero = i - 1;
    for (; i <= last_index; i++) {
	j = zigzag_direct[i];
	level = block[j];
	if (level) {
	    run = i - last_non_zero - 1;
	    last = (i == last_index);
	    sign = 0;
	    slevel = level;
	    if (level < 0) {
		sign = 1;
		level = -level;
	    }
            len = 0;
	    if (s->mb_intra) {
		/* intra mb */
                CODE_INTRA(run, level, last);
                if (len)
                    goto esc0;
                /* first escape */
                level1 = level - intra_max_level[last][run];
                assert(level1 >= 0);
                if (level1 < 28) {
                    CODE_INTRA(run, level1, last);
                    if (len)
                        goto esc1;
                }
                /* second escape */
                run1 = run - (intra_max_run[last][level]+1);
                if (level < 28 && run1 >= 0) {
                    CODE_INTRA(run1, level, last);
                    if (len)
                        goto esc2;
                }
	    } else {
		/* inter mb */
                CODE_INTER(run, level, last);
                if (len)
                    goto esc0;
                /* first escape */
                level1 = level - inter_max_level[last][run];
                assert(level1 >= 0);
                if (level1 < 13) {
                    CODE_INTER(run, level1, last);
                    if (len)
                        goto esc1;
                }
                /* second escape */
                run1 = run - (inter_max_run[last][level]+1);
                if (level < 13 && run1 >= 0) {
                    CODE_INTER(run1, level, last);
                    if (len)
                        goto esc2;
                }
            }
            /* third escape */
            put_bits(&s->pb, 7, 3);
            put_bits(&s->pb, 2, 3);
            put_bits(&s->pb, 1, last);
            put_bits(&s->pb, 6, run);
            put_bits(&s->pb, 1, 1); /* marker */
            put_bits(&s->pb, 12, slevel & 0xfff);
            put_bits(&s->pb, 1, 1); /* marker */
            goto next;
        esc2:
            put_bits(&s->pb, 7, 3);
            put_bits(&s->pb, 2, 2);
            goto esc0;
        esc1:
            put_bits(&s->pb, 7, 3);
            put_bits(&s->pb, 1, 0);
        esc0:
            code = (code << 1) | sign;
            put_bits(&s->pb, len + 1, code);
        next:
	    last_non_zero = i;
	}
    }
}