[MacPorts] #65623: ffmpeg: update to 6.x

[MacPorts]

#65623: ffmpeg: update to 6.x
-------------------------+----------------------
  Reporter:  janngobble  |      Owner:  mascguy
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.7.2
Resolution:              |   Keywords:
      Port:  ffmpeg      |
-------------------------+----------------------

Comment (by mohd-akram):

 My hope is that we can update ffmpeg to 6.0 directly, and make broken
 ports use ffmpeg4. How would one use ffmpeg6 or (the eventual) ffmpeg4 in
 a port? Is it a matter of updating `configure.cppflags` and
 `configure.ldflags`?

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Ticket URL: <https://trac.macports.org/ticket/65623#comment:16>
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