Name: ビデオストリーミングの問題 - Computerphile (Video Streaming Problems - Computerphile)
Uploaded: 2021-01-14T10:16:30.000Z
Duration: 17 min 39 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

過去形

In fact, it's been a problem in various guises, certainly in the UK since digital TV became popular in 1998.

But it's more of a problem now as we watch on different devices, perhaps easy things.

If we demo it, I've got the live tennis from Wimbledon.

This is coming from the area on top of the roof was interesting to be cable or satellite there.

She wouldn't make that much difference, or they do sometimes get delays between the three of them.

If we bring up the same thing on the BBC, I play, which is the online streaming service again, we're saying we want to watch this life on.

We see we got completely different part off the match you and if we would watch it for long enough, we would see that this one was ahead of this one, probably by about 90 seconds to two minutes.

If you're watching on your streaming by your device without your TV, your phone or something, you're going to get a slightly delayed video.

If I bring it up on another computer again, we're watching live by the I fare.

Actually these two aren't in sync either.

Is about a three second delay by something changing on here to that, and we can work out Sean conducing clever things and work out the exact delay between that screen on the streaming one.

Is this just cause it's coming across the Internet?

I mean, these is way to understand why this is happening while we're getting there is actually just have a think about how streaming video work what's going on.

I understand that probably actually works best if we start how we get the picture from the camera on the back.

That video normally sent these days is digital over a signal called HD SD Eye on these run depending on whether it's sth d u h d.

It could be a CZ Lois 270 megabits per second or is high sort of 1.5 gigabits, also for HD and then for you Stu talking up to sort of 12 gigabits of those, sometimes that's carried over four separate cables rather than one single one.

When things were analog and everything went over C R T type displays like the one behind me.

Things were that simple, so we had a camera so on we had TV.

Oh, I display and effectively you could connect to cable between the two.

On this camera would start producing the image.

It would be scanning across the top of the image, and they would do the next line in the next line in the next line.

And someone will see the video on interlaced for how that's no actually done assumes it was started.

Scanning would send the sink course to say, this is the beginning of the line down the cable.

It would then send the analog signal down.

The cable on the C R T display could start displaying that image on screen effectively as soon as it saw the image it was immediately displayed on screen.

The delay was effectively the length of the cable on the speed of light so effectively zero on any sort of terrestrial cable basting.

And even if we punch on Ariel in here as well, fasten Ariel on transmitted it, and we had some sort of receiver here to connect to the TV again, speed of light.

It was fascinating in the old days of analog TV than everything.

What the camera saw could be on your screen within a tiny fraction of a second.

You would see it live even if this was a digital link.

As long as you're not starting to compress it, then you start me, for example, the str connection on Shawn's camera.

We get sent along the same thing that happened.

Things get more interesting when we start to do digital transmission because the bit rate.

So we said it's so high you're not going to send 12 gigabits per second out over the over the air.

And the way that that's generally done is that you take hang on.

I've got the perfect problem for this visual aid.

Before we had video, there was film anyway, So the way that the digital compression where he's rather than working on a single frame, it would takes a region of say, That's a 12.

Of course, what this means is, is that if you've got a compress, the 12 all into related to each other.

So you gotta wait while those sort of Siri's of frames come in.

That's about half a second in U K 50 Hertz land.

If that's all we did, we would have 1/2 2nd delay Next would have to wait for that half second of video to be captured into our compressor.

We compress it and saying, then we can send it, and then we can decompress it.

Actually, they're probably be some decompression delay as we sort of decompressed it as well.

But that would probably only be another frame.

Will say wouldn't be quite as long as this.

Now, you could just do it on those 12 and then you would take the next 12 or so compressed that see it end up with 1/2 2nd delay, and so you can start to see where the delay starts to come from in terms off.

Sending this thing Actually, what you tending to find is it wasn't 1/2 2nd delay it was more like two or three seconds you got on.

Part of that was that you'd actually want to try and do walk, compress things in more than one go so that if your first half second say near needed slightly more bits to encode it in the next half, second needed slightly less.

He could sort of rob from Peter to pay Paul Toe sort of managed a bit rate over a period of time, and then you'd have to buffet at the other end to make sure everything works.

So you're getting a delay because of the way the compression works.

What about if we start to do this over the Internet?

What we've seen that we can send that data down a network connection and get it to display no problem at all.

But the key difference here is that whereas when it's transmitted over the TV, it's board cast, we send the signal.

One sound of the transmitter on anyone who's got a receiving Ariel can receive that signal decoded and watch without network connection.

It's a point to point we send the packets from one machine to another machine, yet we can have broadcast and we can have multicast.

Problem with that is, if you want more than one person to watch it, then you need Maur.

So you've got the computer, which is connected to the camera or the TV network system there.

So the video's going into that, and then he's got a network connection on Dhe for something like the eye player.

That's about five megabits per second on that, sending it out to my computer here.

But then showing decides it is fed up of filming, this computer finally wants to know what tennis is doing, so he connects his computer teary again.

That's another five megabits per second there on so on, and so on somebody, This machine is known to produce 10 megabits, so we're getting your problem.

It's a band with this, you know it takes five megabits per stream.

We want two streams as 10 megabits, four streams as 20 and so on.

Up to 100 megabyte card, you could probably 20 streams and so on.

We could put another computer in here, another server and feed the video.

And then we could actually start adding other people and load balancing them to get there.

And so on on, if we're very clever, what we'd actually do is we start moving these computers to be closer to where they use is also using less of the network.

And so what we could do is actually have this computer here said it was in my local I p.

It could just take the same data coming from this one and send it on toe Shawn's computer, and he could send it on to my computer here on then Captain Brady's as well when Australia were playing.

So actually, we now have five megabits from this on dhe five from each of these, because it can copy the easy out to each of them.

And of course, this is gonna increase the delay slightly, but it's going to be marginal.

Seats are really making it, but that's not explaining why we get those delays.

So we need to build up lots of machines transmitting it, move them closer.

The problem with this approach is that we were sending data from the encoding computer to Brady's machine, my machine insurance machine.

How do we make sure that the packets we want to send here get to these machines particularly ist the way you do?

They're using a system called GDP, not the standard TCP that was doing there.

And you had issues with people's firewalls getting in the way.

So the way they got around that Waas I think Apple first came up with a thing called http Live streaming his equivalents from a daily Microsoft and standard.

It tends to be used now is something called MPEG dash dynamically adaptive streaming over H, D, g, P and the The way this works is sort of on a sort of biggest scale version of what we saw happening at the lower end.

字幕リスト動画再生

ビデオストリーミングの問題 - Computerphile (Video Streaming Problems - Computerphile)

sort

slightly

amount

version