[MacPorts] #61668: ffmpeg 4.3.1: fails to install on Apple Silicon

[MacPorts]

#61668: ffmpeg 4.3.1: fails to install on Apple Silicon
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 Reporter:  jpanetta  |      Owner:  (none)
     Type:  defect    |     Status:  new
 Priority:  Normal    |  Milestone:
Component:  ports     |    Version:
 Keywords:            |       Port:
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 `ffmpeg` currently does not install on Apple Silicon due to
 unsupported/broken dependencies on arm64: `rsvg`, `x264`, `libvpx`, and
 `soxr`. I have managed to fix all of these except `rsvg` with the
 following pull requests/commits:

 https://github.com/jpanetta/macports-
 ports/commit/bd5c4becfb398ffd1b4555e38663448a2208d132
 https://github.com/macports/macports-ports/pull/9252
 https://github.com/macports/macports-ports/pull/9253

 I did not create a pull request for my `x264` commits since I'm not sure
 it is acceptable to use a commit on `master` instead of `stable` (which
 doesn't support Apple Silicon yet). Also, the old PPC assembly patch needs
 to be updated.

 Unfortunately, `rsvg` looks more difficult because of its `rust`
 dependency, so I just disabled it in the commit here:

 https://github.com/jpanetta/macports-
 ports/commit/d282ae91bfabf4dc97af3f592238c03cf6b69051

 Would something like this (restricted to the `arm64` build architecture)
 be acceptable as a temporary workaround?

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Ticket URL: <https://trac.macports.org/ticket/61668>
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