When casting to jellyfin-mpv-shim from jellyfin-web in the browser,
jellyfin-web sends data about which version (for grouped items) and
which streams the user selected in the browser to the
"Sessions/{sessionId}/Playing" API endpoint.
The API endpoint currently doesn't forward them to jellyfin-mpv-shim
through the Play command, which results in the default streams being
played instead of the browser selected ones.
PlayRequest already has the properties and they are already sent to the
cast client by SendPlayCommand when present.
jellyfin-mpv-shim will already use them to select the wanted streams
when it receives the Play command.
All that's needed to make it work is to take the parameters and assign
them to PlayRequest.
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