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

[MacPorts]

#65623: ffmpeg: update to 6.x
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  Reporter:  janngobble  |      Owner:  mascguy
      Type:  update      |     Status:  assigned
  Priority:  Normal      |  Milestone:
 Component:  ports       |    Version:  2.7.2
Resolution:              |   Keywords:
      Port:  ffmpeg      |
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Comment (by i0ntempest):

 I already migrated two of my ports (av1an and mpv) to link with ffmpeg v6.
 mpv would crash in certain cases if linked with ffmpeg v4, which I think
 could be a sign of devs ditching old versions of ffmpeg (at least not
 explicily targeting/testing).

 I know this will be a huge undertaking but I really would like to see this
 migration process starts soon, especially now v7 is released.

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Ticket URL: <https://trac.macports.org/ticket/65623#comment:26>
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