4K is the next big thing in TVs, and 4K videos are starting to pop up everywhere. But 4K video takes up a ton of space, which makes it hard to download and stream in the best quality possible. Thankfully, one technology is changing that, and it’s known as High Efficiency Video Coding (HEVC), or H.265.
It’s taking a while for this new technology to become ubiquitous, but it’s happening—4K UHD Blu-rays use HEVC, VLC 3.0 makes HEVC and 4K videos more watchable on your PC, and the iPhone can even saved recorded video in HEVC to save storage space. But how does it work, and why is it so important for 4K video?
When you watch a Blu-ray disc, a YouTube video, or a movie from iTunes, it isn’t identical to the original raw video that comes out of the editing room. In order to fit that movie on a Blu-ray disc—or make it small enough to comfortably download from the web—the movie has to be compressed.
Advanced Video Coding, also known as AVC or H.264, is the best standard for video compression in widespread use, and there are a few different methods it uses to try to reduce the file size of your video.
For example, in any given frame, it can look for areas that are mostly the same color. Take this still frame of me and my son—much of the sky is the same color blue, so the compression algorithm can split the image up in to chunks—called “macroblocks”—and say “hey, instead of remembering the color of each pixel, we can just say that all of these chunks along the top are the same color blue.” That’s a lot more efficient than storing the color of each individual pixel, which lowers the file size of the final frame. In video, this is called intra-frame compression—compressing the data of an individual frame.
AVC also uses inter-frame compression, which looks at multiple frames and notes which parts of the frame are changing—and which aren’t. Take this shot from Captain America: Civil War. The background doesn’t change much—most of the difference between frames is in Iron Man’s face and body. So, the compression algorithm can split the frame up into those same macroblock chunks and say “you know what? These chunks don’t change for 100 frames, so let’s just display them again instead of storing the entire image 100 times.” This can reduce file size dramatically.
These are just two over-simplified examples of the methods AVC/H.264 uses, but you get the idea. It’s all about making the video file more efficient without compromising quality. (Of course, any video will lose quality if you compress it too much, but the smarter these techniques are, the more you can compress a video before getting to that point.)
High Efficiency Video Coding, also known as HEVC or H.265, is the next step in this evolution. It builds off a lot of the techniques used in AVC/H.264 to make video compression even more efficient.
For example, when AVC looks at multiple frames for changes—like the Captain America example above—those macroblock “chunks” can be a few different shapes and sizes, up to a maximum of 16 pixels by 16 pixels. With HEVC, those chunks can be up to 64×64 in size—much larger than 16×16, which means the algorithm can remember fewer chunks, thus decreasing the size of the overall video.
You can see a more technical explanation of this technique in this great video from HandyAndy Tech Tips:
Again, there are other things going on in HEVC, but that’s one of the biggest improvements—and when all is said and done, HEVC can compress videos twice as much as AVC at the same quality level. This is particularly important for 4K video, which takes up a huge amount of space with AVC. HEVC makes 4K video much easier to stream, download, or rip to your hard drive.
HEVC has been an approved standard since 2013—so why don’t we use it for all videos already?
These compression algorithms are complex—it takes an awful lot of math to figure this out on-the-fly as a video is playing. There are two main ways a computer can decode this video: software decoding, in which it uses your computer’s CPU to do that math, or hardware decoding, in which it hands the load off to your graphics card (or the integrated graphics chip on your CPU). A graphics card is far more efficient, as long as it has built-in support for the codec of the video you’re trying to play.
So, while many PCs and programs can attempt to play an HEVC video, it might stutter or be very slow without hardware decoding. So, HEVC doesn’t do you much good unless you have a graphics card and a video player that both support HEVC hardware decoding.
This isn’t a problem for standalone playback devices—4K Blu-ray players, including the one in the Xbox One, are all built with HEVC in mind. But when it comes to playing HEVC videos on your PC, things get tougher. Your computer will need one of the following pieces of hardware in order to hardware decode HEVC video:
You will also need to use an operating system and video player that supports not just HEVC video, but HEVC hardware decoding—and this is a bit spotty at the moment. Many players are still adding support for HEVC hardware decoding, and in some cases it may only work with certain chips from the list above. At the time of this writing, VLC 3.0, Kodi 17, and Plex Media Server 1.10 all support some form of HEVC hardware decoding, at least for certain cards. You may have to enable hardware acceleration in your player of choice for it to work properly, though.
As time goes on, more computers will be able to handle this kind of video, and more players will support it more widely—just like they do with AVC/H.264 now. It may just take a while for it to become ubiquitous, and until then, you’ll have to store your 4K videos in AVC/H.264 at giant file sizes (or compress it more and lose image quality). But the more HEVC/H.265 becomes widely supported, the better video is going to get.
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