Join Maxim Jago for an in-depth discussion in this video About codecs and resolutions, part of Media Composer 8.7 Essential Training: 110.
- [Instructor] This is a good moment for us to run through the various screen resolutions you might encounter, and the Avid DNxHD and Avid DNxHR codecs, and why you might choose one rather than the other. I'm going to run through this pretty quickly, although I think it's fair to say you could go very deeply into this compression technology. So, first of all, let's start out with resolutions, and I'm going to go pretty fast as I say. First of all, we've got anything described as high resolution, or I suppose, what ought to be called Ultra High Resolution, is anything larger than Full HD.
And Full HD is 1920 by 1080, so anything bigger than that. And then if we run down the list here, of course, we've got HD which is 1920 by 1080, there are a few other variations, of course, and anything higher resolution than standard definition video is technically called HD, but, if we're going to describe Full HD, it's 1920 by 1080, and that still has a 16 by nine aspect ratio. If I jump through a couple of the 2K options here, you can see that we've got a 1998 by 1080 pixel, 1.85 to one version of 2K.
And then, we've got Full Raster 2K, 2048 by 1080. Both of these are described as DCI compliant, or let's say they are deliverable image resolutions you could use if you're producing a DCP for theatrical distribution. Next up, we've got UHD, so, very often this is referred to as 4K, but it isn't exactly 4K. The names 2K and 4K come from a parallel standard that was developed for cinemas, at the same time as the tv broadcast standards.
And so, it's not exactly a 16 by nine aspect ratio, however, TV manufacturers often confuse the two, I suppose, because, UHD is a harder thing to explain than 4K. Everybody gets 4K. But, if you're working in the professional media industry, you'll find that people do know the difference. But, UHD, is 3840 by 2160, and it's an exact match for the aspect ratio of HD, or 16 by nine SD for that matter. And then we've got, again, a 1.85 to one version of 4K, and there's full DCI compliant 4K, which is 4096 by 2160.
Now, of course, we're looking at 8K, and, once again, when people refer to 8K, what they're really referring to is another form of UHD. And, of course, anything over HD is Ultra High Definition, so we have 7680 by 4320, which is four times larger than UHD, at least the 4K UHD. And you can see the model that we get ourselves into. I'm guessing that the industry will settle down on referring to UHD as meaning 3840x2160, and 8K as referring to the four times resolution version of that, 7680 by 4320.
It matches the aspect ratio, it's still 16 by 9, but it's not true full 8K, which would be double on each axis, our 4K DCI cinema raster. It's well over 8,000 pixels wide, though it does have the same vertical resolution. So, we're still settling down on the standards for 8K, and we're going to see, I suppose, what happens as consumer TVs and cinemas ramp up support for this very very high resolution format. So now, let's take a look at our Avid DNxHD codecs.
Now, I want to draw your attention, in particular, to the HD part of this, and let's just run down. We've got DNxHD 36, 145, 175 and 220X. And you can see from the Data Rate column here in my list, that the number just represents the number of bits or megabits per second, so it's the data rate, the amount of data per second that's used to store the video information. Of course, the perception of quality is subjective, but, as you can see from our descriptions here, Avid themselves have in mind, a particular target function for these data rates.
Offline, of course, is for packing in as much content as you can into your available storage, and maximizing playback performance, cause it's easier to play back. A lot of broadcasters using DNxHD 145 as their delivery standard, and if you're producing high quality broadcasts, so, let's say, high-end costume dramas, you might go for 175. Literally, the difference is, the amount of data used to store the picture information. And as you get into longer and longer edits, it becomes increasingly a concern. The distribution standards for broadcasters are based on perceived quality, and if the audience is happy with 145 megabits per second, then that's probably enough.
But if you're working on very high end production, it's likely you'll want to go for the DNxHD 220X, and the X, as you'll find in a lot of places indicates 10-bit. We don't have time here to go into the difference between 8-bit and 10-bit video or graphics, but I will say, that 10-bit is double and double again, the gradient, if you like. It's the number of steps that go from off to on for each pixel, and it means you will get a much more subtle color and you'll never see banding or posterizing in your image.
It's a lot of work for the system to play back, and you can see here, it's a much higher data rate, and as Avid describes it, it is a cinema quality 10-bit finishing codec, but hey. If you're working on a major budget feature film, you can put all the hardware you need into the system to be able to work with that kind of media. Again, I want to draw your attention to that Avid DNxHD description. These data rates specifically relate to working with HD footage, and not to working with Ultra High Definition or 4K footage.
So, let's move on to our DNxHR codecs, and notice that these are described as independent, they're actually resolution independent. The HR in this case refers to High Resolution, and you're going to use this codec if you're working on 4K or UHD media. So, we've got DNxHR Low Bandwidth, and rather than specifying a specific data rate here, we're looking at the amount of compression applied, and that gives us a range of data rates.
And the reason is, of course, that it's resolution independent, if you're working on a higher resolution clip, then you're going to have a higher data rate. So, we've got low band, which is, I suppose, for our offline work. Standard Quality, SQ, which is compressed seven to one, and the compression ratio literally means the file gets that much smaller. It's that much smaller than uncompressed media, which would be ridiculously enormous. Then we've got HQ, High Quality, 4.5 to one, and we're now getting into the gigabits per second, instead of the megabits per second for some of our resolutions.
And then HQX, and again, that X indicates that we're working at 10-bit. Notice that this is a higher level of compression, but it's 10-bit, so the resulting quality is that much higher. And, finally, we've got DNxHR 444, cinema quality. This is all of the color information for all of the channels and with just 4.5 to one compression. And just look at that data rate. That goes up to 3.73 gigabits per second of data.
And where does all of this information leave us in terms of choosing formats and codecs and working with our media? Well, as usual, the answer is that you plan backwards. Start with your requested deliverables in mind, make sure you have a discussion about what you're supposed to be delivering. And, if necessary, you might need to work offline and then come online and re-capture or re-import your media at a higher data rate, and, as long as you know that these options exist, and it's just a question of choosing them in a menu, you're good to go.
- Importing and transcoding media
- Creating a group clip
- Syncing picture and sound clips
- Making quick edits such as stringouts
- Recutting a scene
- Creating subsequences
- Pacing a scene with Media Composer's trim tools
- Mixing sequence audio
- Working with high-res media
- Retiming video
- Nesting effects
- Keying video
- Animating titles and graphics