In Part One we looked at the basics of wireless technology and the five categories of wireless transmission that can happen on a video production. In this part we’ll look at each category in detail, and survey the various wireless video technologies available.
Let’s start with the most ubiquitous category.
Device-Network-Device wireless transmission
The defining feature of this category is the ‘Device’. The device need not be a camera or a video-centric tool. It’s basically anything that resembles a computer – laptop, smartphone, tablet, television, etc. Another key feature of this category is that you can connect to multiple devices via one network.
There are two types of networks:
- Ad-hoc Wi-Fi network
In the first case, somebody has to set up a wireless network, and every device must support one of the commonly available Wi-Fi 802.11 standards. In the second case, everyone needs a data plan (with sufficient speed and signal strength) that connects to the Internet. We have seen earlier that mobile Internet connection speeds are far lower than current wi-fi speeds, though they are quite sufficient for compressed video streaming. Smartphone advertising is at an all time high, so you probably know all the cool things we can do with them nowadays. They sky’s the limit.
If you secure this network via a password, then only your crew will see what you share. You can also set up a server (a laptop or an Android smartphone, nothing fancy) and control who gets to see what, within the network.
Of course, if you’re all packed into one room, it is easier to just say it.
Device to Device wireless transmission
The difference between this category and the former is that this category does not set up a network to talk to multiple devices. Its goal is to just link two devices to achieve a specific transmission of data. The best example of this is wireless follow focus and remote control, like what you can find in an Arri Wireless Remote System (WRS).
The defining feature of this category is that the wireless connection between two devices is sometimes proprietary, and only designed to fulfill the function of the network. E.g., Arri does not share details about this standard simply because it doesn’t want any third-party device interfacing or interfering with its functionality.
Another example of a wireless focus system is Hocus Focus, which utilizes a 433-434* MHz range with 10 channels to choose from, and can reach up to 200m (600 feet).
However, two ‘computer-type’ devices can also communicate directly via:
- Wi-Fi Direct
Wi-Fi Direct is implemented in the latest Android phones, and Bluetooth is ubiquitous but without a clear path to the future (many say Wi-Fi Direct will replace Bluetooth). The underlying technology isn’t that important because the manufacturers ensure the connection works, and that’s all that matters. Remember, these connections don’t require the existence of a wireless network, just the two devices.
The common problems when pairing smart-devices are the same as file-sharing across any two disparate computers:
- Operating system and file system problems.
- Application and file-type compatibility problems.
- Not everybody on set will have compatible devices.
*A note about frequencies:
Many companies choose to release products in what is called ISM or license-free bands. These are slices of spectrum that are usually made available for industrial, scientific and medical (ISM) research. The cool thing about ISM bands is that any device operating in these bands must tolerate any other device – with no recourse to protection from any body or government. The other way to look at it is you can experiment and create wireless systems without following universal standards. This allows many manufacturers to build proprietary products that cannot be seen by consumer wi-fi devices.
The most common bands are 2.4 GHz (which is why microwave ovens run on them) and 5.8 GHz (it is close to 5 GHz). But there are many others as well. The important thing to remember is that the frequency allocation for ISM is different for different countries. So, don’t go about creating something and then fly it to a country where you might land in trouble for using it.
Audio to Audio wireless transmission
This category is only second in usage to device-network-device, because the data rates are so low. Most video productions utilize some form of wireless audio transmission, especially in the form of wireless lavalier mics.
The Sennheiser G3 wireless lavalier system operates between a frequency range of 516-558 MHz with 1,680 tunable frequencies (channels) within that range (25 KHz per channel). This is within the limits of human hearing (20 Hz to 20 KHz). The Sennheiser EM 100 G3 receiver has a frequency range of between 516 to 865 MHz. Let’s not forget that we need both a transmitter and a receiver – it operates just like a walkie-talkie, but with data always going one way.
As a side note, you can also connect dynamic and shotgun microphones with wireless transmitters. E.g., the Sennheiser SK 100 G3 transmitter is compatible with the Sennheiser MKE 400 run-and-gun shotgun mic. As long as the input mic-level signal is compatible, it’ll work. In any case, wireless audio always has inherent risks with interference, so use them wisely.
There are mixers with wireless connectivity – mostly to allow them to be controlled by tablets or other control devices. However, production mixers usually prefer to be connected to physical cables. Bottom line, any audio device can be made wireless, using common available wi-fi technology. There are no technological limits (you can transfer high-quality audio via USB 2.0), and the only two things you should be concerned about are:
- Quality and fidelity of the audio
Wireless headphones are usually designed to work over bluetooth, simply because the range is always assumed to be less than 30 feet. One of the advantages of bluetooth is the lower chance of interference. The other advantage is low power draw.
Video to Video and AV to AV wireless transmission
This is where things get interesting. As we saw in Part One, consumer wi-fi standards are not going to cut it for serious video production. To know the current data rates and technologies available on a film set, read Understanding the limits of data rates and transmission.
Audio bit rates are so low that most devices that focus on high-end video transmission also include audio in their streams, whenever available. This is why I’ve clubbed them together.
You could classify (just for understanding) AV-AV systems according to their use scenario, as (these are my terms, forget them at the end of the article):
- Encoders (high latency)
- Streamers (low latency)
The reason encoders have high latency (in case you didn’t know, latency is the delay between the event as it is being recorded, and the arrival of it at another point – a display or whatever) is because they need to process data and transcode them to a heavily compressed format that can be streamed over conventional consumer level wi-fi networks.
One such system that does this is the Teradek Cube:
The Teradek Cube is a system that comes in two parts: An encoder and a decoder. It sets up an ad-hoc wi-fi network (802.11n, dual band 2.4 and 5 GHz, also has a master mode at 5.8 GHz) and can stream compressed video to the decoder as well other devices that can connect to the network, like tablets and smartphones, etc.
The latency of the Cube is as follows:
- Just compression: 60 ms
- Total latency from encoder to decoder: 300 ms
E.g., if you are recording at 24 fps, then 300 ms represents about 8 frames. Let’s say you are a skilled focus puller, and your mean reaction time is going to be approximately 200 ms. Add in the time it actually takes time to turn the focus knob, and you’re looking at a fastest possible time of one second from the event as it happens. In the real world, through the pressures of production, age and dexterity, location, and a million other factors, this duration will be higher than one second.
Is this good or bad for focus pullers? If you’re shooting at a low f-number (say f/2 or thereabouts) and at a longer focal length, an interview subject can only move about 2-5 inches before going out of focus. When shooting 4K material, this is immediately obvious. Ask yourself, how fast can you move your head forwards or backwards by 2-5 inches? Inexperienced (and even experienced) erformers and actors do this all the time, and it is the job of the focus puller to stay alert and react as quickly as possible. Even at a gentle rocking speed, I can cover 2 inches in less than a second. If my wireless focus pulling system has a latency of 300 ms at its best, I’ve already lost.
To be fair to the Cube and other devices like it, they are not meant to be used for critical focus pulling. The advantage of such systems is that they are cheaper to manufacturer, and the technologies used are already available widely (namely HD-SDI, H.264 and 802.11n in the case of the Cube). As long as your device can connect to a wi-fi network, you can receive streaming video. With a maximum data rate of 10 Mbps, it’s good enough for 5 simultaneous streams of client-monitoring and video villages, as long as the encoding quality level is high. The higher the data rate, the higher the latency. With an iPad or iPhone, expect 10-15 seconds of latency.
Here’s a video that explains how to get the best out of the Cube:
Streamers are what you want for:
- Critical focus pulling
- Live switching
- 1:1 monitoring (mimicking an HD-SDI, HDMI or 3G-SDI feed)
The ultimate goal of a streamer is to reach zero latency (impossible) with zero signal loss (possible with digital technology).
For the sake of comparison, let’s look at a device that attempts to do this: the Teradek Bolt.
Here’s a comparison between the Bolt and the Cube:
|Wi-fi technology||WSDI Pro||802.11 a/b/g/n|
|Frequency||5 GHz||2.4 / 5 / 5.8 GHz|
|Data||2.97 Gbps||10 Mbps|
The major difference is the proprietary WSDI Pro (TM) wireless technology used, which is pretty similar to WHDI in results.
It can transmit a 3G-SDI signal (1080p60 10-bit 4:2:2) to 4 receivers, so one Bolt system (1+4 devices) can serve a focus puller, a DIT for critical monitoring, a director/DP and an encoder like the Cube – which will stream the video to 5 other people who are too lazy or scared to stand behind the DIT or DP to watch the footage.
What is the latency of the Bolt? It is less than 1 ms, according to Teradek. Here’s a video demonstration:
What other options are available in the market? Here’s a quick comparison of some wireless AV-AV systems (click to enlarge):
#Pricing and specifications might be totally inaccurate. Check the manufacturers’ websites for correct information. The price includes the cost of one transmitter and one receiver.
##SDI/HDMI option available at an additional cost.
###The kit is put together by Gefen and Atomos parts but works great according to AbelCine.
One important consideration I’ve left out is power draw. Wireless devices consume lots of power (just like smartphones do when connected to a data network) and you must study the kind of options available (like connector, power draw, etc.) prior to purchasing. I have tried to avoid comparing the above systems as a whole, and have solely focused on the wireless technology.
As you can see, most manufacturers are probably opting for the WHDI standard at the moment, and none have incorporated WirelessHD or WiGig systems for 2K or 4K material. They all offer a latency of < 1 ms (most of them, anyway) so focus pullers can get the job done. Going by the prices, openness to share information and industry ‘street-cred’, I’d say the Teradek Bolt looks like a solid deal, though the AbelCine system shows you that you can put together a wireless HD streamer system on your own if you wanted. By the way, this is not an endorsement of either product.
This brings us to the end of our article. I hope it has given you enough information to understand the concepts, problems and solutions available as far as wireless video technology is concerned. The big question you need to ask yourself is: Is going wireless worth the cost benefit?
What do you think? Has going wireless added any tangible benefits to your workflow?