RedShark News

05 Oct

Why you should use Avid DNxHD and Apple ProRes

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So, what’s so good about ProRes and DNxHD?

What’s good is that they don’t compress the video as much. They trade storage space and bitrate for quality and ease of processing. They typically need ten times as much storage. That’s a lot, but hard drives are tending towards being free, so it hardly matters these days.

In fact, ProRes and DNxHD (sometimes called “intermediate” or “production” codecs) sit in a kind of “sweet spot” between the humongous data rates of uncompressed video, and the egregious processing demands of Long Gop video.

Why not just work with uncompressed?

Because you need as much as six times more storage and data bandwidth than you do with ProRes and DNxHD. Even with disk prices as low as they are, that’s asking a lot. Moreover, you’ll find yourself unable to process as many streams of uncompressed video in real time: you’ll hit a brick wall once your disk system maxes out. ProRes and DNxHD are so processor-friendly, that even though your computer has to uncompress multiple streams on the fly, you’ll probably find you can edit more simultaneous streams than with uncompressed.

But what about quality?

Both ProRes and DNxHD are effectively “visually lossless” at their higher bitrates. That means exactly what it says: you can’t tell the difference between your original video and the same material encoded to ProRes or DNxHD.

So you don’t need to worry about generation loss. In fact, you can usually make many copies in the intermediate codec format without any apparent degradation.

It’s worth stressing that the main reason for ProRes and DNxHD’s increased quality is that they are not long-GOP codecs

Once you’ve converted, your edits will fly. These codecs are so efficient that you can play multiple streams with a fraction of the effort you need for a single stream of H.264 - based video. As an example, on my Macbook Air, playing any HD Long-Gop clip will cause the fan to come on at full power within seconds, but with ProRes, I can play a clip - in much higher quality - with no sign of the fan.

 


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  • When Avids DNxHD codecs first came out we ran them up against our uncompressed DS suite and pushed a whole load of material through comparing the results on our CRT HD grade 1 monitor and you just couldn't see any losses in the DNxHD content.
    The only real issue I've seen has been when DNx185 content has been laid off to HDCAM (with it's horrid sub sampling and compression) and then re-captured as DNx185. Artefact's start to appear and quality quickly falls away depending on the content and the original acquisition codec used.

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  • You mentioned in this article that "Transcoding to an intermediate codec is not your only option." But I was wondering how comparable (in image quality) is transcoding to intermediate codec against capturing in a intermediate codec.

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  • If you capture from uncompressed directly to an intermediate codec, that will be better than transcoding from a Long GOP codec like H.264.

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David Shapton

David is the Editor In Chief of RedShark Publications. He's been a professional columnist and author since 1998, when he started writing for the European Music Technology magazine Sound on Sound. In his day job, David has worked with professional digital audio and video for the last 25 years.

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