I have run this cam for several years now with two 2560x1440 15FPS, and two 704x480 15FPS (both h265). The entire time have noticed channel 2 never reaches and sustains 15fps, but fluctuates quite a bit centered around 6fps with bitrates around 350k, while channel 1 stays solid at 15fps with bitrate around 500k (mainstreams). I wasn't really sure why this was happening.
Recently I had some free time to experiment with it, and managed to get both channels stable using 10fps/10keyframe interval (same resolutions as before). The bitrates are both holding solid ~500k now. After considering why and doing some mental math estimates, it appears as though these cameras may be limited by a 10mbit interface, no? It's wired with cat6 to a gigabit poe switch. On that switch all of my dahua cams are showing a 10/100 connection. I haven't dug into my switch webui yet, but I suspect they're all on 10mbit phy, and the camera is prioritizing channel 1, and capping channel 2 to stay in range of the connection limits. If that's the case, it would explain why the single 4k cams can do 15fps no problem, but these dual cam setups have issues if you try and push them beyond 10mbps combined (either framerate or resolution reduced on one or both cams).
Anyone else have this observation, or am I trippin'? I noticed the above post mentions 1080 res on one of the cams, which sorta supports this theory.
[edit: Indeed, they all are on 10mbps phy. This totally explains why you will have issues trying to run both cams at 4k 15fps. Therefore I suggest users of this camera do some basic maths during setup, and choose resolution/framerates/encoding to suit your situation whilst keeping the bandwidth <10mbps.
I suppose it would be nice if Dahua put a 100mbit poe connection on this camera, to make better use of it's potential.
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