The VMI Guide to Easy Streaming

A brief article to streaming to the web.

Watching video images on the web has become as ubiquitous as being able to book cinema tickets or do your grocery shopping on-line!  Youtube makes the uploading of video images childs-play too, so consequently, in 60 days, more video footage is uploaded to YouTube, than the combined production output of all US Broadcasters over the last 60 years, so it must be easy!

However, arranging a live webcast has always has a certain mystique and as a consequence, live video streaming has been often considered to be in the ‘dark arts’ category – that is, until the release of the next generation technology, such as the AJA Io XT/Thunderbolt, which makes it very easy!

This article will explain in easy steps the equipment and tools needed in order to arrange a live webcast.

Firstly, streaming requires video compression, so you are well advised to ensure that you begin with the best video source quality possible.  Grain or noise are incompressible and will eat your bandwidth, so ensure that you light your subject well and don’t use any gain setting in the cameras, unless low light levels make this absolutely essential.  You will anger your client if the connection drops, and the best way of ensuring that this does not happen is to use HD-SDI and not HDMI – you have been warned!

Next, ensure that you work with a digital feed to begin with.  HD-SDI or SD-SDI are best of all but HDMI will work, providing you don’t have any movement in the cables, as HDMI connections can be a bit temperamental and you definitely need a solid connection to create a solid feed!  Avoid systems which use a composite video connection, as any downconversion to composite PAL will necessarily introduce adverse noise and artifacts, which will hinder the quality of your Broadcast.

You need a reliable internet connection – this is obviously an anathema, since the internet is, by design a bit temperamental and discrete packets of data are not fully compatible with continuous video feeds, so ensure that you have checked the quality of internet feed that you plan to use in advance to ensure that it works at the desired bit rate.  It goes without saying that you should have lots of headroom in your connection – in other words, work well within the available bandwidth, to avoid problem with any spikes.  Working with a laptop will enable you to connect to the internet either with a cable or via Wi-Fi and even via a cellular service if this works for you.

Now for the important bits.

Decide on the resolution and image size of the streaming feeds that you will be using.  The most common are interlaced and progressive and there are many settings of resolutions (from 3G all the way up to SD and HD 1080) and it is quite common to simultaneously broadcast High Quality and Low Quality feeds. The software that you use for streaming will advise on what quality levels are available to you at the quality of internet connection, so experiment with what works for you in advance.

AJA IO XT box – really useful for streaming

You will also need a computer IO Box and for this to work best of all, a Mac or PC with Thunderbolt connection is best for connecting to your video source.  Thunderbolt is the new input/output connection invented by Apple which allows a bus speed of 5Gb/second or even 10Gb/second when going working from solid state-solid state, thus allowing truly fast data throughput.  It also allows you to daisy chain a number of peripherals and for the data to be transferred from the AJA Io/XT box to the Mac, to the drives and then on to a Monitor.  The design of the bus and PC means that the external hard drives ‘knows’ that they are taking the media data to store and the monitor ‘knows’ that it is extrapolating just the monitor image data but using one Thunderbolt chain means that the data transfer is lightning fast and the connectivity is both really simple and also reliable.


We favour the use of an I/O box called the AJA IO XT, which we no longer carry from stock, though this functionality is commonly available now at low cost.  This is a very versatile machine, which can work in multiple configurations and this is just one application for it but here is the simplest connectivity required for live streaming:

Procaster Live Streaming Application

A very easy application which VMI has tested for streaming is the popular live-stream program, Procaster available as a free download.  It is both easy to configure and allows simultaneous differing-resolution feeds for everything including iphone and ipad streams on their servers. 

As mentioned previously, the quality of internet connection is very important but don’t worry if your internet connection is poor, as a live stream will still be possible and the Procaster application will simply delay the broadcast by some seconds, so that any ‘holes’ can be easily ridden without interruption.  Trying this out at VMI over a copper internet connection led to a 30 second delay but this resulted in a very solid feed which did not break over a very long test transmission!  Breaks in transmission will obviously annoy your viewers, so this definitely gets our thumbs-up!

The AJA Io/XT accepts an HD-SDI BNC input, which as already mentioned, is very solid and much better than composite video or HDMI.  Audio can be emdedded into the video signal to ensure that video and audio are broadcast in sync and time code is also embedded into the same signal for simplicity and reliability. The AJA device also has an HDMI if you really want to use it, subject to the caveat about using the best type of signal for break-free feeds…  HDMI also has an 8bit limit, does not support some HD feeds like 24p, has only limited embedded metadata and no time code support – do I need to give any more reasons not to use HDMI but HD-SDI instead!

The system is designed to be able to stream over the cellular network, though we have not tested it and is clearly subject to the limitations of mobile phones, so we would not recommend this for mission-critical applications, though the facility is provided for it you want it – better in this situation to use a local hotspot, such as BT Openreach on demand etc and then you can put your video-village where you like and not have to be close to a wired network point and use Wi-Fi for internet connectivity instead.

A Shallow Depth of Field can reduce the size of the Streamed Images

Lastly, some advice on actual material suitability.  In order to stream most effectively, you really want to have the smallest data stream possible and make the video codec work as easily and reliably as possible.  In order to do this, I have already mentioned that you should avoid video noise but stylistically, avoid pans and too much picture information changing at the same time.  The amount of data in the image also affects data size and the Depth of Field can affect the size of the video streams as well.  VMI did a study last year of the effect of having a shallow depth of field on the size of streamed images Shallow DoF good for Streaming and found that by using cameras with a large sensor and thus a shallower depth of field, it can actually reduce the data bandwidth requirement of the same images by 10% or more, so our advice here is to use large sensor cameras and throw the unwanted material out of focus to reduce the size of your streamed images!

You can even use applications, like Veescope Live for real-time chroma-key mix and overlay, record in Prores codecs for easy post production and simultaneously stream to the internet for your clients to see – so many applications are now possible!

More useful stuff about the AJA Io XT

Apart from enabling a mac with a thunderbolt connection to connect to an external recorder, the AJA Io XT also has the ability to record footage onto a separate thunderbolt drive with a separate thunderbolt output from the Io box (The AJA box has 2 x thunderbolt interfaces).  

In doing so, there is no need for transcoding or down-conversion of footage and has the added benefit of handling dual HDSDI 444 output without having to go through the Mac.  This enables full 4:4:4 images to be viewed from RED onto professional large monitors using thunderbolt using the 5Gb/s stream or 10Gb/s if one works from solid state to solid state.

These files can be massive and traditionally we would have down-converted them SD in order to use older firewire or USB interfaces. Thunderbolt handles much bigger streams very reliably and the AJA can manage and manipulate simultaneous routes of differing resolutions and do this whilst streaming live!

This means that you can take a very reliable HD-SDI HDSDI feed into the workstation or laptop via thunderbolt and avoid any need for down-converters.  Since there are separate audio inputs into the AJA box as well, you can also avoid using audio embedders, if your audio is not already embedded in the signal.  This greatly simplifies wiring and enhances reliability and functionality.

Gerard Botha,

VMI Head of Cameras,
July 2012 (Olympic month)

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