字幕表 動画を再生する 英語字幕をプリント [MUSIC PLAYING] DAN COFFEY: All right. Hello, and welcome back to another week of exploring digital media. This week we're going to talk about the basics of video production. We have wrapped up our still photography component which has been a lot of fun. It's been really fun to see what you guys have done. We're excited to see your projects. And so now we move into the world of video, where we're talking about more than just one frame at a time. So speaking of which, as I said, we've been focused on one frame. But now our camera is literally capturing at high speed multiple frames at a time. So there's a lot more that we have to think about as we do this. So we refer to how many times we see an image per second as the frame rate for a video. And what is the frame rate of film? Like, you go see a movie in the theater, what is the typical frame rate you'll see? Anybody know? IAN SEXTON: A few answers from online. DAN COFFEY: Yeah? IAN SEXTON: We'll see 24 frames per second. DAN COFFEY: 24 frames per second. Yes. Yes, exactly. And certainly this graphic shows 60 FPS, 60 frames per second. What IS 60 frames per second? Why choose one versus the other? That's kind of some of what we're going to unpack a little bit tonight. But how about broadcast television? How many frames per second is that shown at? AUDIENCE: 24. DAN COFFEY: 24. No, actually, it's not. So it goes back to some old standards, but 60 frames per second is what broadcast television is sent at. And that doesn't mean that the content that you're viewing was recorded at 60 frames per second necessarily. But it has been conformed to 60 frames per second as you watch it back. All right. So as far as frame rate goes, this all kind of comes down to human perception. And how do we determine that 24 frames per second is the-- how did that become the standard for film making? So let's look at a couple of clips here, starting with just three frames per second, as you see on the top right corner. Let's watch this and see how this little clip feels. And to be clear, this is a video that was shot at a higher frame rate and has been conformed to three frames per second. But the effect is the same. How did this motion feel? Very unnatural, right? Very kind of not pleasant to watch. You're noticing every single frame rather than watching the motion of the people walking. So let's jump ahead here. Here's six frames per second. How does this one feel? We're getting there. We're kind of still seeing quite a bit of judder, as we refer to as a frame rate that is very low and kind of clunky like that. Let's move ahead to 12 frames per second. OK. Is that starting to feel a bit more like a natural motion? Yeah? And let's double up one more time. Let's go to 24 frames per second, as we've already discussed as the standard frame rate for film. And so this kind of comes down to what it is that we're looking at. We're looking at a group of pictures in a rapid succession. That's all video is. It's encoded a bit more smartly than that, but at the end of the day, you're really just looking at pictures being-- it's like a flip book you open and flip through very quickly, the images move forward. So 24 frames per second has kind of become the standard. Does anybody know the reasoning for why that was initially the standard back-- I don't even know the year that it was established. But-- IAN SEXTON: I actually don't know off the top of my head either. So I should look into it. DAN COFFEY: So we'll look that one up. But 12 frames per second is kind of where we start to not be able to distinguish the difference between the still images being flashed before us. But 24 frames per second is the standard. So my question is why. No? Go ahead, Alec. AUDIENCE: I was just saying, to save money for 24 frames-- DAN COFFEY: Yeah. Well, that's actually interesting. That's a part of it. So on this film strip here, we had 24 frames per second. I'm sorry, where you have your film, you've got your picture encoded alongside your audio. So the audio track actually ran alongside the picture. And one of the reasons-- film is not cheap, so we wanted to find a way to use as little as possible. But we also needed to have enough fidelity in the audio that it sounded nice and clear and sharp and was not too muddy and that you could actually understand it. And 24 frames was a good frame rate for that-- didn't cost too much, you had a good natural motion to it, and you had good audio fidelity. So that's kind of where the standard was set. So the audio, as I said. And so as we define our frame rate, we can kind of pick and choose this. If you open up Shotcut or Adobe Premiere, or whatever nonlinear editing system you're using, you can say, hey, I want my project to be at this frame rate. And so you can also additionally set your camera and say, I want to shoot at 24 frames per second. I want to shoot at 30 frames per second. I want to shoot at 60 frames per second. It kind of depends on the hardware that you're actually using. But common frame rates that we might see-- 24 is equivalent to what we usually see for film. A common video standard is actually 30 frames per second. The soap opera effect where everything is very smooth, that comes down to a 60 frames per second playback. And then you've got some higher frame rates at the other end that can be used for specialty things. So you might have a camera where you're kind of saying, hey, how do I actually set my frame rate in my camera? And so if you've got a Canon, it might look like this. If you've got a Nikon, like this, and a Sony, like this. And the idea is that you're going to choose your frame size, the actual width by height, as well as how many frames per second. And so looking here at top left with the Canon frame size, we've got 1920, which is short for an HD frame, or 1920 by 1080 as the resolution, at 30 frames per second. The "ALL-I" in this case just refers to how the frames are actually encoded and means that it's easier for a non-linear editing system to actually access every frame. When you get these IPB frames, it's just a lighter weight version of encoding where it's harder to decode is really what we need to know. But it's much more space efficient. So if you're given this option on a Canon camera, choose the ALL-I. And so you can choose 30 frames per second, 24 frames per second, or you can jump down to the next, the smaller resolution of HD video, which is 1280 by 720, or 720p for short. And so you can choose either of those as well. You know, Nikon looks pretty much the same. And with Sony, you actually need to choose your Kodak, what the video is actually being stored as. Kodak is simply that kind of container that holds all the frames together and defines how it is actually encoded. But we don't need to know those details. We just need to know that you can actually choose on this camera. And if you're using Sony, XAVC is just the newer video codec that they are using. So choose that. And then you can choose what frame rate and frame size you want. All right. So overcranking and undercranking-- does anybody know what these terms mean offhand? We're talking about frame rates. That's a little hint. This "jif" here-- or GIF, however you want to say it-- is a hint as well. Overcranking, what might this be? Any guesses from online? So what is this hand doing as it cranks? What's happening? What are we looking at? We're looking at an antique camera. But we're seeing two kind of things happen in the camera. We're seeing this kind of wheel go around, and we're seeing this bar here kind of slide up and down. Any guesses? AUDIENCE: Does it mean maybe that the [INAUDIBLE] the succession of the images up and down? DAN COFFEY: Yeah. Benjamin is saying is this actually control the speed, the images moving up and down. So this is the shutter that we're seeing. We're used to talking about shutter speed from still photography. And then this is the-- I don't know what this is technically called, but it advances the frames of film down through the camera as it moves. And in the old school cameras, it literally was a matter of kind of keeping a constant crank going to determine your frame rate. IAN SEXTON: It's called the claw. DAN COFFEY: The what? IAN SEXTON: The claw. DAN COFFEY: The claw. OK, yes. So the claw hooks into the perforation on the film and pulls the frame down. And so what happens if you start to crank this more quickly? You overcrank. The film advances faster. And so what is the effect of that if you were to play it back? AUDIENCE: Fast motion. DAN COFFEY: Well, fast motion is what you would think. You record a lot of frames very quickly. But if you were to play them back at your normal frame rate, the 24 frames per second, it's going to be slow motion. So it's kind of counterintuitive in that sense. But it's because you're cranking very quickly, recording a lot of data, and then playing it back more slowly, you get slow motion. So we thought to kind of show what this example looked like, we'd set up in this beautiful Harvard Library and recruit a boxer to kind of come in and show us what different frame rates can look like. So here we go. We've got Conor Doyle here being a guest for us. So yes, just a little hint as to what the setup looked like. So the things we want to keep in mind here, I've kind of alluded to these, are the captured frame rate-- this is the frame rate that you set your camera to, how many frames per second you're recording-- versus your project frame rate or your timeline frame rate-- how many frames per second are being played back over the sequence. And they matter. If they're the same thing-- so here, if you look at the top right of this frame, we've got 24 frames per second being played back at 24 frames per second. This is going to be a real time playback. So as we watch this, Conor's punching the punching bag here. All right, feels like normal time. If you were standing there watching him, this is the speed at which it happened. But if we look at-- we overcranked here, we cranked very quickly, we recorded 250 frames per second. And we play it back at 24 frames per second, roughly how-- what's the time delta here? How many times slower is this going to be? 10 times? Yeah. Because 24 times 10 is 240. We'll round up to 250. So 250 frames per second, his punching should be about 1/10 of the speed of normal time when we play it back. And here it is. So it really matters here, what is it that we want to do? Do we want to slow things down? We need to shoot at a higher frame rate. But how much higher do we need to shoot? And that depends on how fast your sequence is, how many frames per second you're going to playback that your viewer is going to watch. All right.