• some common questions of NDI

    Introduction to the basic features of NDI and answers to some common questions

    NDI is relatively hot recently. What is NDI, how to use it, and what benefits it can bring are all vague. Friends often ask some basic questions. Here are a few frequently asked questions to make a brief description...

    Brief description of features:

          NDI is the abbreviation of Network Device Interface, that is, network device interface protocol. After the audio and video signal is NDI encoded, it can transmit and receive multiple broadcast quality signals in real time through the IP network. At the same time, it has the characteristics of low delay, accurate frame video, mutual recognition of data streams, and communication.

           The application of NDI refreshes everyone’s understanding of traditional system signals and production pipelines. It simplifies the construction of the system and the transmission, calling, and multiplexing of various signals in the system with a new network application layer form, making system design, Integration, application, maintenance, function expansion, etc. are simpler and more flexible.

          In fact, many foreign TV stations have converted the traditional SDI/HDMI video transmission form to NDI network transmission.

          Okay, not much gossip, start answering questions...

    Question 1: What kind of transport protocol is NDI? What are its advantages over traditional hardware?

       Answer: NDI is an audio and video codec and network transmission protocol (based on UDP), which means it has a duality. The first is to encode and decode the video, and the second is to perform low-latency transmission on this basis; It is used for local area networks, not for large networks. (Many friends think that NDI can push and pull streams on large networks. This is a misunderstanding; if there is a static IP, NDI can be used on large networks, but the bandwidth is too high and the environment is very difficult. It is difficult to build, so the use of large networks is currently not realistic and has universal significance).

       In addition to being able to transmit broadcast-level audio and video network streams, NDI also supports some signaling specific to radio and television, such as the commonly used TALLY and two-way conversations for directors, support for PTZ camera control, support for Alpha transparent channels and other important functions commonly used in the field. Moreover, NDI is not afraid of format incompatibility. Try to recognize any format in software. This is not available in many traditional hardware. The traditional site requires multiple devices to be combined together. The channel machine is too expensive and not suitable. For small and medium-scale live events, the picture below is a typical small-scale live broadcast scene with a traditional switcher:

           This picture is not a criticism of the hardware of a friend, so don’t misunderstand the position. The equipment in the picture is big, well-tested, and very popular. But to realize the basic live broadcast function, you have to stack each piece of hardware to form it. A live broadcast system is very troublesome, the wiring is inconvenient, and the system needs to be compatible, and it takes time to debug. It is often impossible to find the cause of the problem. The on-site investigation time is tight and anxious, and there is suspicion everywhere. .I believe that the old irons with rich field work experience can deeply appreciate the taste... And the transmission characteristics of NDI, a switch and network cable can completely save a lot of hardware, and the indicators meet the broadcast level. vMix is easy to use, why not try it?

       The most important thing about NDI is its network properties, typical of professional audio and video IP, high indicators, short delay, easy to call, easy to find signals, easy to set up a system, can transmit control signaling... these are what NDI has Real competitiveness.

    Question 2: Why do people always say NDI HX and FULL NDI, what is the difference between them?

    Answer: NDI is divided into two categories, one is NDI HX, the other is FULL NDI; HX is a variant of H.264, and it has been iterated to HX2. HX has a higher compression rate for original video, and the HD bandwidth is about 20- 40M, the delay of NDI|HX is larger, between 100-300ms; FULL NDI is based on I frame (also called key frame, the algorithm based on I frame is the best way to restore the original image) shallow compression, It is a broadcast-level IP indicator. It has been iterated to NDI4.5. The bandwidth is relatively large. The HD bandwidth is 90-180M, and the 4K bandwidth is 200-300M. The target is the broadcasting and ProAV market, where the definition is high.

    Question 3: What is the NDI delay? (Everyone is most concerned about this issue)

    Answer: Regarding the delay, FULL NDI delays 30-200ms. The delay data depends on the network situation and front-end equipment. FULL NDI itself delays about 1 frame (20-30ms); when NDI is actually used, the network delay may exceed 100ms In most cases, if the network conditions and terminal conditions are better, 50-100ms is relatively easy to achieve, and the time wasted by the display terminal is often the longest.


    Question 4: Can one box encode multiple NDI or decode multiple channels?

    Answer: Regarding encoding and features, each NDI box can only encode one camera or video source signal or decode one NDI source. The boxes currently on the market do not support one box to encode and decode multiple NDI channels. The bandwidth of NDI can be adjusted. , But there is not much room for adjustment. Generally speaking, if the FULL NDI bandwidth is adjusted below 60M, the image may appear to be faint.

    Question 5: What kind of switch is used?

    Answer: Regarding the switch, if there are multiple video sources and signals, FULL NDI must use a gigabit switch (with POE function is better to solve the problem of on-site power access), a single channel can be directly connected to the laptop; the live software will directly recognize the network The NDI signal in the Internet; it is recommended to use a POE switch, preferably a big brand with guaranteed quality, and the network situation will be relatively better.


    Question 6: What does NDI encoding and decoding mean? how to use?

    Answer: Regarding encoding and decoding switching, most NDI boxes support encoding and decoding in one, and can be switched at any time in the web UI (you can log in to the network with a mobile phone), such as ScienceImage's FULL NDI series box; The meaning of NDI encoding and decoding is unclear: encoding is to encode audio and video signals into NDI network streams into the switch or PC, and then be discovered and called by the PC or software in the network;

    Decoding is the other way around. Control the box to restore the NDI stream in the network (select when there are many NDI streams, one box can only decode 1 NDI stream) and restore it to SDI/HDMI signal through the box output to the local monitor, TV, Recorders or other equipment or terminals that require SDI/HDMI signals.

    Question 7: If I use an NDI box, what software can I use?

    Answer: At present, there are a lot of NDI software and NDI-supporting software, such as the famous vMix, OBS, StreamStar, Wirecast, etc., including the live broadcast and industry software or editors made by many domestic companies that support NDI. Another example is the popular network application. Software and platforms Skype, ZOOM, etc. also support the NDI protocol. IP-based is the general trend. NDI is highly professional, easy to use, and has small delays. It uses soft directors for live production and live broadcast, and gradually replaces the traditional capture cards, matrixes, and directors. The way of hardware transmission and production. The following figure is a typical application diagram of NDI:


    Question 8: How is NDI applied on the Internet?

    Answer: The real advantage of NDI is the network characteristics, that is, its network discovery. The box encodes the signal source into an NDI signal and then enters the network (the local area network can have multiple network segments and can cross network segments), and all terminals in the network ( PC or director software) can find all NDI sources in the network for calling and production in real time, similar to the concept of network matrix and distributed, there can be multiple NDI encoding terminals (pushing NDI into the network), multiple NDI Decoding end (pull NDI stream for local display or recording, etc.).

          The application of a large number of channels will reflect the advantages of NDI. The efficiency improvement brought by the characteristics of convenient networking and potentially powerful network management attributes is beyond the reach of traditional hardware and connections...

    Question 9: What other uses and applications can NDI have?

      Intranet uses high-quality NDI encoding and decoding, large network uses RTSP and SRT and other UDP-type transmission protocols with small delay, which will be a very good combination; intranet NDI real-time call and production, and external network uses SRT for point-to-point remote Transmission is undoubtedly the most dynamic and competitive match at present.

      For a simple example, you can also try to use wireless bridge or Wifi to transmit FULL NDI. Some friends from provincial TV stations use WIFI6 wireless router to transmit NDI stream to vMix in the live broadcast scene. When wireless NDI image transmission is used, The effect is stable and good...

    Question ten: How stable is the NDI network? I am afraid that there will be an accident at the scene.

           This question is very sensitive, and it is also one of the issues that everyone is most concerned about. In fact, the NDI box itself is very stable. The FULL NDI box is basically developed on the basis of FPGA. FPGA is a programmable logic device, which is difficult to develop. High and stable, high-end equipment is generally customized with FPGA, so there is little risk of crash or disconnection when the box itself outputs NDI.

            There may be risks in the network system. If the network is not well set up, this problem will occur. It is recommended to choose a better switch and network cable. Do not install any messy other software on the machine or laptop. vMix itself is relatively stable. A well-configured PC is still more important. The key lies in human experience. If the above unnecessary risks are effectively avoided, then it is more reliable to use NDI to direct the production...

    Current and future application scenarios of NDI:

    Broadcast production

    Conferences and seminars

    Major events


    Broadcast over the Internet

    school activities

    Live sports

    Religious events live

    Large-scale Internet Conference

    Live stage

    Medical live broadcast

    Distributed large screen application

    Wedding scene production


    ScienceImage FULL NDI series

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