Streaming Video Tips And Tricks For Video Producers – Taming The Video Compression Monster
This article is specifically aimed at video producers who are interested in getting the most out of their streaming video productions in terms of video and audio quality. It mainly involves the best working practices for ensuring that your streaming video wrestles well with that dastardly beast, the “compression monster”, which wants to turn all your pristine video to digital mush.
I came from a background in professional video and media production in Perth, Western Australia, shooting TV commercials, independent film, corporate video, and much much more. With the advent of the internet, I became excited about the possibility of using it as a way of delivering quality streaming video advertising for businesses both in Perth and around the world. So I founded my current business, ONLINE AURA, and went into developing video specifically tailored for streaming. The problem was, although I was familiar with the theory of video compression, the most I’d ever come up against this beast was at the level of VHS or DVD production, where it occasionally wrangled but never inflicted serious damage upon me. The reality of video streaming compression was a huge adjustment however, as I watched pin sharp images shredded into digital mud before my eyes, and heard glorious soaring music turned into a horrific sequence of farts and dying bumblebees.
Over the course of time, through experience of testing and producing many streaming videos for local clients, I learnt the best practices and techniques for shooting and editing streaming video. I won’t say I’ve tamed the compression monster, because he still lurks over my shoulder on every shoot, but I will say that I’ve learnt how to keep him under control and make it through the video compression process with just a few scratches here and there. So this articles includes a number of tips and guides to help you battle this beast in your next streaming video production.
1. Let there be Light – I’ll start with the most obvious and what can be considered as one of the most crucial aspects in producing quality video streaming. I know there’s a lot of things written about this recommending strongly-lit flat lighting (i.e – no shadows). The theory being that reducing contrast in your image means that it will compress more efficiently and you’ll end up with a higher quality streaming image. This isn’t quite right, as the human perception of “sharpness” relies on contrast differences, and even though a higher contrast image may in mathematical terms be less well compressed at a pixel by pixel level, it will create the illusion of being sharper to the viewer. Basically the rule for best quality is to provide a smooth ratio of contrast, and to favor large soft sources that don’t over light what you’re trying to shoot. Blasting light directly from your camera position over the entire scene is not going to produce favorable results in terms of streaming video quality. The best results come from soft directional sources, but there’s also room for backlighting and other creative approaches.
You have to make allowances for the eventual compression, but that generally means keeping your image contrast within an acceptable ratio. Low light is obviously a problem, and night shooting can be difficult. Any grain is going to play havoc and awake the old compression monster, who will hungrily eat up every little vibrating pixel. You can use grain removing plug-ins, but they can have the effect of softening your image and will compress sometimes even worse. Crushing your black levels entirely can sometimes help, and de-saturating your image and adjusting midtones can also be useful. If you have to shoot in low-light on the street, try not too using the gain controls on your camera, and instead go for a low shutter (if your camera has it). Lower shutter speeds will generally compress better. For interview subjects in the studio, I generally use a soft key and a bit of a kicker or backlight, with just a little bit of frontal fill. For video compression I make sure the background is relatively static and defocused. Using green screen and replacing the background with a blurred still image or slowly moving blurred background works well, and keeping background colors muted helps compression.
2. Camera movement – Obviously a lot of fast camera movement is going to require higher rates of compression for streaming video. But different types of movement also have different effects. A smooth dolly shot will actually compress reasonably well but, interestingly enough, the same move-in or out using a zoom instead will not compress well, and generally zooms are to be avoided if possible. Hand-held images will tend to suffer greatly, unless they are stabilized later using a software plug-in such as Steadymove. Steadicam shots can work reasonably well if done well. Unfortunately most steadicam shots contain a bit of ‘float’ which, although barely perceptible to the average viewer, will not compress as well as a genuine dolly or track shot. Locked off shots will obviously compress best, though it is dependent on what’s in front of the camera!
3. Motion in front – Certain things compress well, while certain other things compress poorly. Water and waves look beautiful and crystalline on DVD, but in the streaming video world they fall to pieces. They carry took much randomly moving fine detail. The same with leaves blowing on a tree in the wind. If you’re shooting an interview or spot with someone in front of a tree with fine leaves on a windy day, you should consider moving them to take in a background with less motion. Obviously you want to have things moving in your camera frame to provide interest (that’s the whole point of having video over a slide show), but think ProstaStream about how much of the frame is moving. If you can isolate your moving subject with a longer lens and have the background blur out, that will compress better and also appear sharper to your viewer. Because of the small screen size, when shooting people move in a bit tighter. Close ups can be most effective.
4. VBR and the art of “compression accounting” – You should know that using Variable Bit Rate for your video will provide a significant quality boost for most videos over standard CBR (constant bit rate). But to maximize the quality of your streaming video you may need to take advantage of this variable bit rate capacity by doing what I refer to as compression accounting.
What’s that? Imagine I have a budget of $250 per day for a month to buy whatever goodies I want. In a strict CBR world I get $250 at the start of the first day, and, regardless of whether I spent the whole lot or not, it would go back to zero at the end. The second day I’d get $250 again and so on. So, in CBR world, I may as well spend all of my $250, because there’s no saving for the next day. If I see a $800 guitar in the window, I can’t buy it, because I’ll never have that much money, and I have to settle for a poorer quality $200 one instead. In VBR world however, there is saving. If I don’t spend my $250 on the first day, and instead spend $150, that means I can spend the $100 I saved some other time. In effect, I can restrict my spending in the present so I can buy that $800 guitar in the future with the money I saved. If you’ve uncovered the meaning in my torturous analogy, what this means is this – when shooting in VBR mode I’ve got an idea of how many data bits I’ve got to play with and I can spread them out accordingly. Knowing that I want to shoot something with a lot of camera movement, like a dynamic steadicam shot through a crowd of moving people, I know that I should balance that out with a couple of locked off shots with little or no movement. It’s the equivalent of spending $800 on that guitar (the steadicam shot), by scrimping on other days (i.e. shooting the lock-offs). When it comes to encoding, the encoder will look at the video on the first pass, note the amount of movement in each shot and work out an average level of compression for each shot given the total average it has to play with. The steadicam shot might take 800kbps while the lock-off shots only take 80-100kbps. So the trick is balancing out the number of complex and simple shots to take best advantage of VBR compression. With any luck you’ll have a good balance and end up with much better use of compression to give you a better quality streaming video.
5. Shoot progressive – Shooting for streaming video means that you’re producing for a computer screen, which is typically an LCD. The way computer process moving images is fundamentally different from your typical TV. I could write three thousand words about the technical differences, but basically the conclusion is that progressive scanned or de-interlaced video perfectly fits the way a computer monitor displays these images. Interlaced video (which contains fields) displays motion perfectly well on televisions, but will traditionally not encode motion well with streaming video, creating motion artifacts and occasional streaking effects. The best option is to shoot with a camera that delivers images in progressive scan mode. While there are high-end professional cameras, most consumer models won’t. However the prosumer models produced by Canon, namely the XL-1, XL-2 and XM2, all feature a ‘frame’ mode that make these cameras adapt well to streaming video. Failing that, videos should be de-interlaced either at the editing stage using software (e.g Premiere Pro, Avid), or at the encoding stage. Quality encoders such as Canopus procoder typically offer de-interlaced delivery.