Copying the video to the MacMini and playing it directly off the local drive works perfectly, eliminating the MacMini, the video format, and the playback software. My router showed no other network traffic at the time. Leaving me to think it was a problem with the FreeNAS server. When I looked at the server, everything said it was working normally. So I asked here.
Yep, no problem asking. Trying to help debug.
It's still not clear that you've eliminated the streaming setup and/or the networking. Playing a file locally is totally different than playing something over the network off the server. The streaming software and the network have not been eliminated as issues.
When you say "streaming" does that mean you are pointing some playback software on the MacMini at a file on a network share? Or are you using some streaming server like Plex, or DLNA, or something else? If the former, ok there is no streaming server, but it could still be a network issue.
As an example, my FreeNAS runs fine. My Plex server runs fine as a VM with it's .vmdk hosted on FreeNAS and it accesses the media content on FreeNAS via a CIFS share. My hardwired clients play everything flawlessly. My wifi clients sometimes do not play high bitrate stuff without stuttering. It has nothing to do with the Plex server, the Freenas, or the client software. It's the network. My router doesn't show anything either. It's just obvious to me there is interference on the wifi such that its effective bandwidth is limited. So I turn down the quality level and voila! It plays just fine.
But yes, if you have pool errors, obviously fix those first. Then proceed to debug the rest.