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Codec Selection

Course video 14 of 60

In this course, you will see a lot of new words and acronyms you might not be familiar with. If you feel comfortable with your knowledge of tech terminology, feel free to skip these lessons since they will not affect the overall integrity of the course. If you see something that you want to know a little more about, feel free to watch the video to gain insight on some basic concepts. We do expect you to know the majority of this material before going into the next module, we would recommend going through the lessons as a quick brush up.

物联网：通讯技术

加州大学圣地亚哥分校

课程 4（共 6 门，物联网专项课程）

Have you wondered how “Things” talk to each other and the cloud? Do you understand the alternatives for conveying latency-sensitive real time data versus reliable signaling data? Building on the skills from the Sensing and Actuation course, we will explore protocols to exchange information between processors. In this course, you will learn how VoIP systems like Skype work and implement your own app for voice calls and text messages. You will start by using the Session Initiation Protocol (SIP) for session management. Next, you will learn how voice codecs such as Adaptive Multi Rate (AMR) are used in 3G networks and use them for voice traffic in your app. Learning Goals: After completing this course, you will be able to: 1. Implement session initiation, management and termination on your DragonBoard™ 410c using SIP. 2. Discover other users and exchange device capabilities. 3. Compare and contrast narrowband and wideband codecs and experience the voice quality differences between them. 4. Implement and demonstrate VoIP calls using the DragonBoard 410c.

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教学方

Ganz Chockalingam
Principal Engineer
Harinath Garudadri
Associate Research Scientist

脚本

Welcome to the Codec Selection video.

Randy put together a nice little group of slides here for you to kinda talk about

the codecs that are gonna be involved in our venture into VoIP.

>> Right, so as promised, we'll be talking more about codecs.

>> We actually have a whole module on codecs, I think.

>> Right, yeah, we will.

>> Yeah.

>> We'll, more like a broad overview of the [LAUGH].

>> No, yeah, of course, yeah.

>> So, codecs basically, as mentioned before,

encoding decoding digital data signal or some kind of stream.

Some examples we have are FFmpeg, DivX,

or H.264, all these codecs are used.

You might have heard about them, you're might have heard of DivX.

>> Yeah, DivX is a big one.

Yeah, there's also standard codecs that come with each kind of

individual operating system, so to say.

Android has a specific set of codecs that they like to include in their source.

And then you have other codecs, like with Ubuntu,

that they like to include in their source, for example, GStreamer.

But, yeah.

>> So yeah, but then you sort of wonder why can't we just use one codec for

encoding, decoding, why do we need multiple ones?

And that's simply because, depends on what kind of project you wanna take, right?

So, if you have, mostly the argument with lossy versus lossless compression.

So, you have lossless compression, basically it means the picture, or audio,

or video quality is really, really high, but that takes up a ton of space.

Blu-ray DVDs, has 30 to 50 gigs for one movie.

How many movies can you store on a compter if you were to do that,

right, on a normal computer?

>> Yeah, I think compressed movies are sometimes what, five gigs?

>> Yeah, honestly, like I said, it depends on if you want the best quality you can

get or sacrifice some quality but have more, be able to store more.

And also, that ties into video streaming, so if you wanna see super high streamed,

like Netflix videos, you need the different kind of codec

to make sure you'll be able to still stream it at a decent speed, at least.

And then, we also mentioned,

or if you have trouble maybe seeing video or listening to some kind of audio,

it's probably because you're missing some kind of codec.

>> Yeah.

>> Because we encountered that problem once or twice on using Ubuntu, I believe.

>> During the release of Ubuntu, actually during the release of the DragonBoard,

there was a codec that we wanted and it wasn't included.

So, we went on the 96 Board forums, which you should be registered for, and

we expressed our concern and they included it.

So, they do listen everything.

It's a very open community, a very nice community.

And if you're ever encountering something,

hit those forms up and get something going.

>> And then here, I wanted to expand a bit more on codecs versus containers.

So, remember codecs aren't containers.

And then remember containers are just the file extension such as .avi, or .mov,

or .mp4, .wav, etc.

And so, containers just have audio or video codecs,

as well as whatever other data needed for that little container.

So, a container's just a bundle.

So maybe you have subtitles, or some kind of other necessary information for

playback or recording.

And finally, the sections labeled Codec Selection.

So, which one do you wanna use?

I also mentioned this earlier, so it depends.

Do you want lossless compression or do you want lossy compression,

where you have large file versus small file?

It also depends because if you have very slow Internet,

you're probably gonna have to use some kind of lossy compression,

because there's no way you will send a 30 gig file within a decent timeframe.

>> 30 gig file within a two hour movie.

[CROSSTALK] It's possible.

>> That's gonna take a while on a slow Internet.

>> Yeah.

>> And some other factors is the resolution of your files,

how many bits you wanna use to encode or decode, stuff like that.

>> Yeah, but I guess the point right there, is right, so

you use one codec to encode something?

>> Mm-hm, and use the same one to decode it.

>> Yeah. >> Basically it.

>> Yeah, and so, you're actually gonna see our esteemed

Professor Harnoth Garadodgi come back in one of our modules here,

where he will be going over codecs among several other things.

So I think that's in module three, not the next.

Yeah, so two modules from now,

you'll get a chance to check him out and hear some really cool stuff about codecs.

He's actually worked in that field for quite a while, and not

necessarily the codec field but this whole compression, digital signal processing.

He's worked in that field for a long time.

So, he'll have some really interesting stuff to talk to you all about and

hope you stick around for it.

So, that being said, I guess we're good.

>> Yeah. >> With the codec section,

we'll see you in next videos.

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