I think it is showing up as part of the HA stream component. In order to make use of the stream component, you have to have ffmpeg installed. I installed ffmpeg through dietpi-software.
stream: is not a custom component/plugin, but one of the standard makeup of home assistant (https://www.home-assistant.io/integrations/stream/). That said, I noticed there were one or two other packages that I had to install to get the stream component working (unfortunately I cannot remember the details now, but it was all listed and once they were there, stream worked fine - until HA crashed).
I did upgrade HA fully (I did this through homeassistant-update.sh at /home/homeassistant). Once there were issues with stream/FFmpeg, eventually HA just terminated. Having redone the installation but using the 32-bit dietpi image, I have not done anything differently this time, but HA has not terminated/crashed once.
i have seen a similar issue brought up around "error demuxing stream" showing up in the logs, before HA terminates. I don't think this is Dietpi related, but rather some issue with HA and related dependancies.
Really appreciate the input/feedback.
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Okay, good that it works now. A reinstall of HA itself might have been sufficient, as it assures that all Python modules are recompiled (and Python itself) while the homeassistant-update.sh does it only for those where actual updates are available.