[Icecast] can't stream Opus in CAF format

[webmaster at berean-biblechurch.org]

Using FFmpeg, I can stream to a file on disk okay:
    c:\apps\ffmpeg\bin\ffmpeg.exe -f dshow -i audio="Line In (Realtek
High Definition Audio)" -c:a libopus -ac 1 -b:a 32000 live.caf

But, if I add Icey metadata, FFmpeg throws errors: 
    c:\apps\ffmpeg\bin\ffmpeg.exe -f dshow -i audio="Line In (Realtek
High Definition Audio)" -c:a libopus -ac 1 -b:a 32000^
 -ice_name "live broadcast" -ice_description "desc"^
 -ice_genre "genre" -ice_url "https://stream.example.org/live.caf"
-user_agent "agent" -content_type "audio/x-caf"^
 icecast://source:hackme@localhost:8000/live.caf 
[caf @ 00000204b419ac80] Muxing variable packet size not supported on
non seekable output
Could not write header for output file #0 (incorrect codec parameters
?): Invalid data found when processing input
Error initializing output stream 0:0 -- 

Any idea why the destination of Icecast makes a difference?  Is there
something I can adjust in Icecast to make it work? 

Justin
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