multimedia/vlc playback: blackness

[Graham Perrin]

A few weeks ago, VLC ceased to show video.

I hear the audio track but there's blackness.

Debug log, for brief playback of a silent screen recording: 
<https://pastebin.com/cyWJ93RF>

I tried resetting preferences, no improvement.

Any other suggestions?

TIA

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<https://bugs.freebsd.org/bugzilla/buglist.cgi?component=Individual%20Port%28s%29&list_id=354177&product=Ports%20%26%20Packages&query_format=advanced&resolution=---&short_desc=multimedia%2Fvlc&short_desc_type=allwordssubstr> 
no matching bug, so I assume that the issue is specific to my envirnoment.

grahamperrin at momh167-gjp4-8570p:~ % date ; uname -v
Sun 10 May 2020 17:23:40 BST
FreeBSD 13.0-CURRENT #55 r360732: Thu May  7 09:31:34 BST 2020 
root at momh167-gjp4-8570p:/usr/obj/usr/src/amd64.amd64/sys/GENERIC-NODEBUG
grahamperrin at momh167-gjp4-8570p:~ % pkg query '%o %v %R' vlc
multimedia/vlc 3.0.10_2,4 FreeBSD
grahamperrin at momh167-gjp4-8570p:~ %