Quality isn’t everything…
If it was then we would all be shooting, editing and screening 4k Uncompressed 10bit 4:4:4 digital video images. But, of course, we’re not. At a bandwidth of around 1gbps (that’s 1000 megabytes a second) images of this kind of data purity are simply impractical.

In the future, who knows? 4K edited in real-time on I-phone? Certainly not out of the question, but in the mean time every digital image is a compromise in some way.

Frame size, bit depth, compression, colour sub-sampling are all ways to strike that elusive balance between quality and functionality; images that look great but are also usable. DV, AVCHD, HDV, XDCAM, DVCProHD, HDCAM are all shooting/acquisition formats that embrace various compromises in some way between quality and functionality.

When it comes to post-production we have much the same dilemma. In a post-production Utopia, no matter what format the image was acquired in we would transcode and conduct post in Uncompressed 10bit 4:4:4. But this would hit all the same bottle necks of dysfunctionality; namely file sizes of about 10gb/min or more. Similarly storing such files would soak up copious hard drives.

So here again technology has delivered us a sophisticated but accessible compromise, the Lossless Compression Master.

Lossless compression is designed to greatly reduce file sizes without effecting visual quality. Whilst the idea of ‘compression’ has immediate implications for visual quality loss this is a misnomer and the truth is that not all compression is bad. Highly sophisticated algorithms allow for the removal and contraction of image data without reducing the apparent visual quality of the image. Such lossless codecs are perfectly viable as a master format without the unwieldy file sizes of Uncompressed. These codecs also have the advantage of being optimized for editing and playback and so often give superb real-time performance on the timeline. Think of it more as video optimization rather than compression

There are a number of such codecs available. Thus far at IFSS we have utilized Apple’s PRORES 422 codec for both editing and master file archiving. ProRes422 (as the name would suggest) is a 4:2:2 codec meaning it has a greater colour space than the 4:2:0 of DV, HDV and XDCAM and can operate in 10bit colour space above the standard 8bit of most acquisition formats. Both these factors mean ProRes gives a great deal of data accuracy and precision. ProRes files are approx 1gb/min which is 4x bigger than DV and HDV files. But ProRes is still up to 1/10 the size of Uncompressed 10bit HD so its a good compromise.

The downside with ProRes is that it’s specific to Final Cut Pro. You will only have access to the ProRes codec if you have FCP installed. Other software can use ProRes files but only if FCP is installed on the same computer. And of course since FCP only runs on the Mac ProRes is useless if you need cross-platform compatibility.

However, there is an alternative…

Avid DNxHD was one of the first professional lossless compression codecs available and along with other third-party formats like Cineform, was the impetuous for Apple to create ProRes.

The advantage with Avid DNxHD is that it does not require that you own an Avid system. DNxHD is free for anyone to download and use. It utilizes QuickTime and the MOV format and is available for both Mac and PC making it completely cross-platform.

DNxHD uses the same 4:2:2 colour space as ProRes with very similar lossless compression and creates files of the same quality and size. (about 1gb/min for HD)

Avid has all the background info about DNxHD here.

You can download the free Avid Codec Packages here – (scroll down to the bottom of the page)

I now have the Avid DNxHD codec installed on all the main lab computers at IFSS. This will greatly help those students using PC laptops or home computers as you’ll be able to export lossless master files from the school Macs and use them directly on your PC, and of course vice versa; bringing lossless files from the PC to use on the Mac.

The one advantage ProRes still has over DNxHD when used with a non-Avid system is that you cannot capture directly to the DNxHD codec as you can with FCP/ProRes. There is however a potential work-around to this – capture with FCP to ProRes and then use a batch conversion process, such as that in Apple Compressor, to transcode all the ProRes files to DNxHD. You could then take the DNxHD files and use them in any system, Mac or PC.

Regardless of the process above the use of the DNxHD codec for an export master is the same as that for any kind of QuickTime export. When you select the video format or codec for your QuickTime file you will be presented with the long list of QuickTime codecs amongst which will be one labeled ‘Avid DNxHD’. Simply choose this as you would ProRes or Component YUV and away you go.