Output Template, Property Expansion

[pseudoenigma]

Hello, I'm trying to understand something about the output_template= switch in the configs. Here is what it says in the explanation in webm.conf,

# Template string for the output file
# %f - Filename, with extension
# %F - Filename, without extension
# %T - Media title, if it exists, or filename, with extension (useful for some streams, such as YouTube).
# %s, %e - Start and end time, with milliseconds
# %S, %E - Start and end time, without milliseconds
# %M - "-audio", if audio is enabled, empty otherwise
# %R - "-(height)p", where height is the video's height, or scale_height, if it's enabled.
# More specifiers are supported, see https://mpv.io/manual/master/#options-screenshot-template
# Property expansion is supported (with %{} at top level, ${} when nested), see https://mpv.io/manual/master/#property-expansion
output_template=

I'm ready to accept that I'm being a bit dense, but how does this actually work? I've tried experimenting with using ${property} expansion tags even within nests such as %X{${property}} to no avail.

I'm not asking for someone to do it for me, but for the sake of understanding what I might be doing wrong, I'm trying to create a conditional where I can properly name a webm as being from Youtube when I find "youtube" in the path. I have seen ${?path:find('youtu%.?be')} used in the MPV manual, so, while I understand how it can be used in the context of fields where property expansion works, I can't get it to work here despite being advised that it should work. I'm definitely not understanding something!

I would have liked to ask in an email or some other form of communication to avoid opening an issue, but I wasn't able to find any way to talk about this in a more discrete manner. Thank you for reading.

[AKL55]

I'm also trying to set a custom output for my youtube profile. I use "title=${user-data/formatted-date} [${metadata/uploader}] ${media-title}" and tried "script-opts=webm-output_template=" with no success unfortunately.