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In Premiere Pro CS4 Beyond the Basics, Adobe Certified Instructor Chad Perkins explains how to take video editing from simple nuts and bolts to an art form. He shares tips for shooting video in the field to get the most from a subject and get the best footage for a project. He demonstrates how to build a project through the careful use of cutaways, pacing, and suggestive edits. He covers special effects, color correction, and keying and compositing, integrating all these concepts as he builds a music video project from scratch. Exercise files are included with this course.
The other type of compression, continuing on from our discussion in the last movie, is temporal compression, temporal meaning time. So as we talked about spatial compression will look at a frame and then compress that frame while temporal compression will look at a series of frames and see what's different. So it might look at this current frame and then as I go to the next frame, it looks almost identical and the next frame is almost identical, next frame is almost identical, next frame is almost identical.
So we can look at all the pixels that are the same. In the temporal compression method, we will look and see if this pixels the same through the next ten frames, then I'll just remember that pixel and I won't have to make ten different copies of it. I'll just remember that it's basically the same. In other words, it doesn't have to keep track of every single pixel. It's just to has keep track of the changes over time. Now there is a very simplified way of explaining how it works, but that's the basic idea. So spatial compression is again referred to as intraframe compression and temporal compression is referred to as interframe compression and as spatial compression is to image compression then temporal compression is to motion compression.
So it looks it again a series of frames over time and as with spatial compression the more you have action, the more movement you have, then also the more changes you have from frame to frame and the more that temporal compression is not going to be able to compressed things quite as much, because there are all kinds of new information on so many pixels from frame to frame. Now not too many formats use temporal compression and I will tell you why. The ability to use temporal compression really makes small file sizes, because you're not only compressing spatially, but you are compressing in time as well and it really brings file sizes down quite a bit.
The problem is is that these formats have to use something called a group of pictures. It has to has the group say like 20 frames and then look at all those frames and keep those frames together in a whole and then editing them is kind of a nightmare. It's much more taxing on your system. So say for example, let's go to the Sequence dropdown so we have some visuals here. I am going to create New Sequence and we get in this New Sequence dialog box and we see a couple of the big interframe compression methods. HDV is a big one.
MPEG-2 is big one. AVCHD is a big one. These are great formats. They are very optimal compression, but they are very hard to work with when you are editing and again it does take a lot more out of your system to process those files as you're working. It has to kind of unwrap them in a very complex way that slows things down quite a bit. Now one of the new formats that's making a big stir is AVC-Intra. You see AVCHD is a pretty powerful compression method, but it is an interframe, or in other words, temporal compression method.
And so what they have done is they have come out with AVC-Intra, so it uses a lot of the genius of the AVC compression method. But it's an intraframe or, in other words, spatial compression type. So basically it's all the benefits of AVCHD and all the benefits also of spatial compression, which you don't have in AVCHD. So it's my prediction that we are going to see a lot more AVC-Intra in like handheld video and other things, because it's a really optimal format, easy to edit with, because it has spatial compression and yet it does a good job of compressing stuff as well.
So there's a little primer on video compression. I hope that helps. To sum up again, AVCHD, HDV, MPEG-2 those are temporal compression algorithms and often called interframe compression, so they do compress things quite a bit. A lot of quality, very small file sizes. But they are kind of a mother to work with when you are editing. It's often better to use a spatial compression method for the files that you are editing such as AVC-Intra or most of the other file formats.
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