s->mpeg_enc_ctx.codec_id= avctx->codec->id;
static int mpeg_decode_init(AVCodecContext *avctx){    Mpeg1Context *s = avctx->priv_data;    s->header_state = 0xff;    s->mpeg_enc_ctx_allocated = 0;    s->buffer_size = PICTURE_BUFFER_SIZE;    s->start_code = -1;    s->buf_ptr = s->buffer;    s->mpeg_enc_ctx.picture_number = 0;    s->repeat_field = 0;    return 0;}