s->c_dc_scale= s->c_dc_scale_table[ s->qscale ];
s->c_dc_scale= s->c_dc_scale_table[ s->chroma_qscale ];
static void change_qscale(MpegEncContext * s, int dquant){    s->qscale += dquant;    if (s->qscale < 1)        s->qscale = 1;    else if (s->qscale > 31)        s->qscale = 31;    s->y_dc_scale= s->y_dc_scale_table[ s->qscale ];    s->c_dc_scale= s->c_dc_scale_table[ s->qscale ];}