This is not a duplicate of #49595 or #53953, in the sense that what warranted this submission is the lack of other choices when it comes to xHE-AAC decoding. So, unlike encoding, where another encoder, or a standalone CLI tool, or a non-system ffmpeg build, can be used. Playing files with xHE-AAC audio streams requires this to be enabled in the system ffmpeg build.

Sample:
https://archive.org/download/unsorted_files/usac_sample.m4a

This can be played with `mpv` or `ffplay -codec:a libfdk_aac`.

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As a long time Arch user, I remember Arch caring about the "spirit" of licensing when it comes to dependencies. If there was no issue in packaging the libraries themselves, and when there was a clash between user experience and licensing, user experience came first. I think that should continue to be the case. And in that line, providing a "nonfree" ffmpeg package with libfdk-aac support shouldn't be an issue.