Why your DSLR is not a broadcast camera

When DSLR camera manufacturers added video capability to their feature set it opened up an affordable way of creating video to a mass market.  Unfortunately they are not suitable for broadcast applications for a variety of reasons.

The DSLR rise in popularity

The benefits of a DSLR (Digital Single Lens Reflex) camera with video capability were immediately exciting. For the first time we could use the same affordable stills photography lenses for video which opened up a world of creativity.  For example the “filmic” look with shallow depth of field became available to everyone, not just professional filmmakers.

Ten years on and the DSLR remains a popular choice for those who want to combine a video and stills camera in one easy package. I own a Canon 550d which I do occasionally use for hobby video and am happy with the results.  It’s also a great way of introducing yourself to the world of video and how light and lenses interact.

Because the picture quality may look good and the results comparable in technique to higher end productions it’s very easy to fall into the trap of thinking a DSLR is a suitable camera for broadcast work or professional videography.

It almost goes without saying that if your camera’s primary function isn’t video, there will be compromises to shoehorn it in to a device that is designed to do something else!

Rolling Shutter

I had intended to produce a video to explain rolling shutter, and how your DSLR does not capture each frame as an exact moment in time like a broadcast camera does.  But when I saw this youtube video from Smarter Every Day I realised that I couldn’t even come close to the superb, clear and simple explanation that this guy created.

The slo-mo recreation of rolling shutter is impressive and helps us understand the weird picture distortions we see on DSLRs and indeed phone cameras during fast movement.

 

Codec

The rolling shutter alone should be reason enough to know that a DSLR is not suitable for the broadcast environment but we need to consider the recording format too.

For high-end TV production the cameras and post production process normally uses codecs with a bitrate between 100-250Mbps at 1080i resolution with a final delivery for transmission at no less than 100Mbps.  For regional news we ran XDCAM format for capture and post production at 50Mbps.

Most DSLRs capture an mpeg layer 4 video stream at 20-30Mbps. There’s a good reason for this – you can record that kind of data rate onto cheap SD cards.  Broadcast cameras require much faster cards such as Sony SxS and Panasonic P2 formats.  With a DSLR you’re saving money but you’re only capturing a third of the required quality for programme transmission and half of that required for news.  It falls wide of the mark.  Aside from that, most professional editing workflows require mpeg4 files to be converted to an interim codec capable of frame accurate editing, which adds to the time required to compile the footage. In news, that time is crucial for fast turnaround transmission of a breaking story.

Colourspace

Broadcast cameras are designed for broadcast colour space.  A colour space is the range of colours that can be captured or transmitted without error.  Anything outside of this colour space may not display correctly to the end viewer.  This is a documented standard called Rec709 (Rec601 for SD and Rec2020 for 4k).

You can colour correct and limit your footage to Rec709 but to colour correct any video requires the highest possible capture rate to begin with otherwise you start to introduce noise and artefacts to your footage.  It also adds time in the production process.

Interlacing

Like it or loathe it, the broadcast world is interlaced.  1080i is the standard in the UK and until 4k becomes the predominant format which is at least 5 years ahead of us, interlaced will remain.  DSLR’s don’t shoot interlaced, and whilst there are ways of creating interlaced footage you’d need a camera that can handle 50 frames per second and an editing package capable of extracting interlaced fields from that.

EBU

The European Broadcasting Union examines and rates cameras for suitability in the broadcast environment.  The document covers this topic with a lot more technical detail. If you’re serious about broadcast video it’s worth a read of how they qualify cameras suitable for broadcast.  There’s a PDF here.

Technology is changing all the time and DSLR camera capture chips will improve with every generation.  Perhaps in a few years time we’ll have some EBU approved DSLR’s. But we’re not there yet. For now you’re better off getting an HD capable camcorder with a capture bitrate of no less than 50Mbps if you’re looking to provide broadcast video as a service.

Update

Thanks to Stephen Neal who pointed out there is now one DSLR camera approved for broadcast by the EBU and that’s the Canon Eos-1DC.  You can read about the EBU approval here. The retail price is around £6,000 which still seems an awful lot bearing in mind you’ll still need to purchase lenses, and a separate recorder or interface to get professional audio in.  For broadcast work you’d be better off purchasing a Canon XF305 at half the price.

 

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One thought on “Why your DSLR is not a broadcast camera

  1. co-incidentally I was watching that rolling shutter YouTube video earlier this evening before reading your blog Simon!

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