The orig wants a mono output with one of the original channels as signal source. This involves downmixing i.e. rematrixing the audio.
The dupe want to just mute one of the channels, not repan it. One can't apply map_channel to do what the dupe wants.
One can use a couple of methods to achieve the dupe, including pan. But the syntax of pan needed for the dupe case is not the same as the orig, or deducible from it. They need to consult the docs (fortuitously, the dupe case is an illustrated example) or get a direct answer. The 'technique' shown in the orig is not intuitively adaptable to the dupe - one needs to know about the implicit muting that pan applies, which is not documented or evident in the orig answer. So it's not a duplicate of the source Q.
The orig wants a mono output with one of the original channels as signal source. This involves downmixing i.e. rematrixing the audio.
The dupe want to just mute one of the channels, not repan it. One can't apply map_channel to do what the dupe wants.
One can use a couple of methods to achieve the dupe, including pan. But the syntax of pan needed for the dupe case is not the same as the orig, or deducible from it. They need to consult the docs (fortuitously, the dupe case is an illustrated example) or get a direct answer. The 'technique' shown in the orig is not intuitively adaptable to the dupe - one needs to know about the implicit muting that pan applies, which is not documented or evident in the orig answer. So it's not a duplicate of the source Q.