Modify metadata_register API for support individual metric propagation.

[yigithanyigit]

In current state of this API it can only propagate explicitly given features, In other words giving an identifier doesn't work.

For example; for propagating PSNR:
psnr_y, psnr_cb, psnr_cr should be given.

With these changes, propagating individual features and propagating with identifier possible.

[kylophone]

I'm not sure if we need an API like this yet (?). I will hold off on the reviewing this PR until we figure that out. In the meantime, I will reply to your patch in ffmpeg-devel.

[yigithanyigit]

Thanks for the comment,

I found some problems about this patch and I wanted to add for future reference.

After some tests I realized this patch doesn't work expected in some identifiers (VIF, ADM).
The main reason of the problem those identifiers has some conditional features.

For example:

vmaf/libvmaf/src/feature/integer_adm.c

Lines 2707 to 2741 in d95b69e

	if (!s->debug) return err;
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm", score, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_num", score_num, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_den", score_den, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_num_scale0", scores[0], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_den_scale0", scores[1], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_num_scale1", scores[2], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_den_scale1", scores[3], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_num_scale2", scores[4], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_den_scale2", scores[5], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_num_scale3", scores[6], index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_adm_den_scale3", scores[7], index);

vmaf/libvmaf/src/feature/integer_vif.c

Lines 692 to 746 in d95b69e

	if (!s->debug) return err;
	const double score_num =
	(double)vif.scale[0].num + (double)vif.scale[1].num +
	(double)vif.scale[2].num + (double)vif.scale[3].num;
	const double score_den =
	(double)vif.scale[0].den + (double)vif.scale[1].den +
	(double)vif.scale[2].den + (double)vif.scale[3].den;
	const double score =
	score_den == 0.0 ? 1.0f : score_num / score_den;
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif", score, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_num", score_num, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_den", score_den, index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_num_scale0", vif.scale[0].num,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_den_scale0", vif.scale[0].den,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_num_scale1", vif.scale[1].num,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_den_scale1", vif.scale[1].den,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_num_scale2", vif.scale[2].num,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_den_scale2", vif.scale[2].den,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_num_scale3", vif.scale[3].num,
	index);
	err |= vmaf_feature_collector_append_with_dict(feature_collector,
	s->feature_name_dict, "integer_vif_den_scale3", vif.scale[3].den,
	index);
	return err;

As you see those features going to append if debug enabled. However my implementation going to add those features anyway:

vmaf/libvmaf/src/feature/integer_adm.c

Lines 2757 to 2767 in d95b69e

	static const char *provided_features[] = {
	"VMAF_integer_feature_adm2_score", "integer_adm_scale0",
	"integer_adm_scale1", "integer_adm_scale2", "integer_adm_scale3",
	"integer_adm", "integer_adm_num", "integer_adm_den",
	"integer_adm_num_scale0", "integer_adm_den_scale0", "integer_adm_num_scale1",
	"integer_adm_den_scale1", "integer_adm_num_scale2", "integer_adm_den_scale2",
	"integer_adm_num_scale3", "integer_adm_den_scale3",
	NULL
	};

We should handle this somehow. Maybe we can add an option to VmafMetadataConfiguration.

Thanks