* The parent codec must call MPV_frame_start(), ff_er_frame_start() before calling this function.
* The parent codec must call ff_er_frame_end(), MPV_frame_end() after calling this function.
* This function does not use MPV_decode_mb().
+ * lowres decoding is theoretically impossible.
* @param w pointer to IntraX8Context
* @param dquant doubled quantizer, it would be odd in case of VC-1 halfpq==1.
* @param quant_offset offset away from zero