[gentoo-user] slot conflict for media-libs/x264-0.0

[allan gottlieb]

(I have been offline for a few months and apologize if this has been
covered.)

I had not synced for about 3 months (fear of new, incompatible gnucash)
but have now done so.  Unsurprisingly my normal update world shows many
entries and also unsurprising is a blocker (slot conflict).  However, I
am confused by the message which reads

!!! Multiple package instances within a single package slot have been pulled
!!! into the dependency graph, resulting in a slot conflict:

  media-libs/x264:0
  
    (media-libs/x264-0.0.20170701:0/152::gentoo, ebuild scheduled for merge) pulled in by
      (no parents that aren't satisfied by other packages in this slot)
  
    (media-libs/x264-0.0.20160712:0/148::gentoo, installed) pulled in by
      >=media-libs/x264-0.0.20130506:0/148=[abi_x86_64(-)]
      required by (media-video/ffmpeg-3.3.6:0/55.57.57::gentoo, installed)

Why is this a conflict since the first one 0/152 seems to permit other
solutions.  Is the (unstated) point that the second one 0/148 is not one
of the acceptable "other packages in this slot".

Also I seem some advice.  Should I be first working on this blockage.
Or should I instead try to deal with some of the easy updates.

thanks in advance,
allan