GF_Err gf_media_hevc_change_par(GF_HEVCConfig *hvcc, s32 ar_n, s32 ar_d)
{
	GF_BitStream *orig, *mod;
	HEVCState hevc;
	u32 i, bit_offset, flag;
	s32 idx;
	GF_HEVCParamArray *spss;
	GF_AVCConfigSlot *slc;
	orig = NULL;

	memset(&hevc, 0, sizeof(HEVCState));
	hevc.sps_active_idx = -1;

	i=0;
	spss = NULL;
	while ((spss = (GF_HEVCParamArray *)gf_list_enum(hvcc->param_array, &i))) {
		if (spss->type==GF_HEVC_NALU_SEQ_PARAM)
			break;
		spss = NULL;
	}
	if (!spss) return GF_NON_COMPLIANT_BITSTREAM;

	i=0;
	while ((slc = (GF_AVCConfigSlot *)gf_list_enum(spss->nalus, &i))) {
		char *no_emulation_buf = NULL;
		u32 no_emulation_buf_size = 0, emulation_bytes = 0;

		/*SPS may still contains emulation bytes*/
		no_emulation_buf = gf_malloc((slc->size)*sizeof(char));
		no_emulation_buf_size = avc_remove_emulation_bytes(slc->data, no_emulation_buf, slc->size);

		idx = gf_media_hevc_read_sps_ex(no_emulation_buf, no_emulation_buf_size, &hevc, &bit_offset);
		if (idx<0) {
			if ( orig )
				gf_bs_del(orig);
			gf_free(no_emulation_buf);
			continue;
		}

		orig = gf_bs_new(no_emulation_buf, no_emulation_buf_size, GF_BITSTREAM_READ);
		mod = gf_bs_new(NULL, 0, GF_BITSTREAM_WRITE);

		/*copy over till vui flag*/
		assert(bit_offset >= 0);
		while (bit_offset) {
			flag = gf_bs_read_int(orig, 1);
			gf_bs_write_int(mod, flag, 1);
			bit_offset--;
		}

		/*check VUI*/
		flag = gf_bs_read_int(orig, 1);
		gf_bs_write_int(mod, 1, 1); /*vui_parameters_present_flag*/
		if (flag) {
			/*aspect_ratio_info_present_flag*/
			if (gf_bs_read_int(orig, 1)) {
				s32 aspect_ratio_idc = gf_bs_read_int(orig, 8);
				if (aspect_ratio_idc == 255) {
					gf_bs_read_int(orig, 16); /*AR num*/
					gf_bs_read_int(orig, 16); /*AR den*/
				}
			}
		}
		if ((ar_d<0) || (ar_n<0)) {
			/*no AR signaled*/
			gf_bs_write_int(mod, 0, 1);
		} else {
			u32 sarx;
			gf_bs_write_int(mod, 1, 1);
			sarx = hevc_get_sar_idx((u32) ar_n, (u32) ar_d);
			gf_bs_write_int(mod, sarx, 8);
			if (sarx==0xFF) {
				gf_bs_write_int(mod, ar_n, 16);
				gf_bs_write_int(mod, ar_d, 16);
			}
		}
		/*no VUI in input bitstream, set all vui flags to 0*/
		if (!flag) {
			gf_bs_write_int(mod, 0, 1);		/*overscan_info_present_flag */
			gf_bs_write_int(mod, 0, 1);		/*video_signal_type_present_flag */
			gf_bs_write_int(mod, 0, 1);		/*chroma_location_info_present_flag */

			gf_bs_write_int(mod, 0, 1); /*neutra_chroma_indication_flag */;
			gf_bs_write_int(mod, 0, 1); /*field_seq_flag */;
			gf_bs_write_int(mod, 0, 1); /*frame_field_info_present_flag*/;
			gf_bs_write_int(mod, 0, 1); /*default_display_window_flag*/;

			gf_bs_write_int(mod, 0, 1);		/*timing_info_present_flag*/
			gf_bs_write_int(mod, 0, 1);		/*bitstream_restriction*/
		}

		/*finally copy over remaining*/
		while (gf_bs_bits_available(orig)) {
			flag = gf_bs_read_int(orig, 1);
			gf_bs_write_int(mod, flag, 1);
		}
		gf_bs_del(orig);
		orig = NULL;
		gf_free(no_emulation_buf);

		/*set anti-emulation*/
		gf_bs_get_content(mod, (char **) &no_emulation_buf, &no_emulation_buf_size);
		emulation_bytes = avc_emulation_bytes_add_count(no_emulation_buf, no_emulation_buf_size);
		if (no_emulation_buf_size + emulation_bytes > slc->size)
			slc->data = (char*)gf_realloc(slc->data, no_emulation_buf_size + emulation_bytes);

		slc->size = avc_add_emulation_bytes(no_emulation_buf, slc->data, no_emulation_buf_size);

		gf_bs_del(mod);
		gf_free(no_emulation_buf);
	}
	return GF_OK;
}