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  1. Member
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    Nov 2020
    United States
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    I am working on building a live streaming system for my church and have settled on using PTZOptics cameras for the project. Our AV dealer wanted to set them up with SDI connections and then go through a capture device. For cost reasons I am looking at using the IP video capability of these cameras instead.

    In my research I found that the SDI version of their cameras sends out an IP video stream using RTSP/RTMP, while the NDI cameras use NDI HX or RTSP/RTMP for $440 more.

    We are currently using OBS to combine the sound from our mixer with the feed from a webcam before sending it to Facebook.

    As I've looked over the options from PTZOptics I have a question about the advantages/disadvantages of using NDI over RTSP/RTMP? The closest I've come to an actual comparison is a PDF of talking point slides that simply said "NDI evil" - not very helpful. Any insight someone can give would be appreciated.
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  2. Member Cornucopia's Avatar
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    Oct 2001
    Deep in the Heart of Texas
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    I'll make a few comments...

    I don't know the ptzoptics models you've been looking at, but IN GENERAL,
    You have to weigh the priorities of COST, QUALITY, operational EFFICIENCY, and LATENCY.

    AFA cost and quality, it usually works out to (highest to lowest):
    1. SDI
    2. NDI
    3. IP

    AFA operational efficiency, it depends on the rest of your setup. But if you have the right equipment, it probably is (best to worst):
    1. NDI
    2. SDI
    3. IP

    AFA Latency (not counting A/D which is usually ~<1 frame, or <40ms), the spread depends again on what equipment you're using. SDI could be being captured straight to a bus card, and that wouldn't add more than at most another frame's worth. Or it could be being captured via a USB2 or USB3 device, and then the latency might increase by 40-60ms or more.
    IP cams often depend on which codec they're using to send out. Raw YUY2/YV12 codec options are high quality with almost no latency, but they are rare and usually only on the more expensive models. MJPEG is common, and it has fairly low latency, but it's almost always a bit more than either the SDI or NDI offerings. MPEG2 is worse (100+ms), H264 is worse still (160-250+ms), and H265 is worse still (not worth counting). And there is going to be some latency added with decoding more compressed streams as well, the more compressed, the more latency.

    Note that there is a big difference between true, full NDI which probably is ~100-150+Mbps per stream and has very small latency (likely slightly more than SDI+USB3), and NDI-HX, which is much more compressed (~25Mbps per stream) and has noticeably higher latency. AVOID NDI-HX if you can afford it. True NDI is fine. NDI-HX might bug you.

    There is an NDI plugin for OBS that makes inputting multiple streams much easier (though not as easy as using a Newtek device, nor as low latency).

    I consider IP-based sources to be the lowest option, both quality and especially latency-wise. If you are attempting to do realtime video processing work, IP cameras will break you or drive you crazy with their latency.

    SDI is SDI (coaxial serial digital, using a standard pro video protocol). It is NOT IP-based.
    Those cameras (model?...) might be able to simultaneously be putting out both an SDI signal (via coax) and an IP-based signal (via ethernet cable). That IP-based signal will be compressed compared to the SDI signal (which is never compressed). With compression comes a reduction in quality, a reduction in bitrate, and an increase in latency. As mentioned, those will vary depending on the codec choice.

    Not sure if you have looked into ClearOne. I use them all over the campus I manage (I am the AV department for an entire university). The Unite 200 PTZ cam supports simultaneous HDMI, USB3 (unfortunately NOT USB2 backward compatible, and only using the YUY2 signal), and IP-based (using MJPEG, or H264 codecs). I decided to go with connecting the cams via Active HDMI cables (usually 50-100 feet), then capturing those with a Magewell USB3 device at the computer. It gives us real nice uncompressed 1080p60 with only ~60-80ms latency. I would have gone with a USB3 extender or with an HDMI extender, but both were way too expensive. That's one quite good thing about SDI - long cable runs are OK. BTW, HDMI has more latency than SDI, but less than NDI.

    Hope that helps,

    Last edited by Cornucopia; 19th Nov 2020 at 21:34.
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  3. Member
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    Nov 2020
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    Thank you for your information.

    I knew that SDI was going to be the best quality but not a very good option.

    We're an Episcopal church built in the 1940's primarily with concrete. Years ago when installing our PA system the mixer and radio mic receivers were all located in a closet in our Columbarium chapel. For easy access to the mixer our streaming computer has also been located there. When we started this project there was strong opinion that we keep it as unobtrusive as possible - so no dedicated equipment booths in the Nave. Because of the design of the building, running cables of any sort to the Columbarium is difficult - expensive on the front end and difficult to upgrade later. Finally the equipment to control the system that our AV provider insisted on was not very friendly to teach un-technical inclined volunteers to operate and we really don't have the budget to pay a technician every week.

    Because of this SDI is going to have to stay an option of last resort.

    The Columbarium is also in a far corner off of the Sanctuary - too far away to run HDMI without flaky extenders.

    Soon after we started live streaming due to COVID I took the camera from our Logitech Rally video conferencing system and set it up with a laptop running OBS and the NDI plugin to connect that laptop to the streaming computer so the latency is something I'm familiar with and with our workflow hasn't presented a problem.

    I'll have to look at ClearOne. I had looked at PTZOptics first because when our AV provider wanted to install them, I looked at their specs and found that there were over 250 preset positions I could program and I could send the full range of commands to them via a simple HTML GET request - perfect for me to write a simple button based html app for a tablet. Press a web button at each part of the service and a script fires off commands to the cameras - mixer - and OBS as needed. Perfect for low tech volunteers to operate and fits in well with an Episcopal service.
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