s->mpeg_enc_ctx.avctx= avctx;
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;}