Quality Evaluation

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Do curso por University of California San Diego

Internet of Things: Multimedia Technologies

86 classificações

University of California San Diego

Internet of Things: Multimedia Technologies

86 classificações

Curso 5 de 6 em Specialization Internet of Things

Content is an eminent example of the features that contributed to the success of wireless Internet. Mobile platforms such as the Snapdragon™ processor have special hardware and software capabilities to make acquisition, processing and rendering of multimedia content efficient and cost-effective. In this course, you will learn the principles of video and audio codecs used for media content in iTunes, Google Play, YouTube, Netflix, etc. You will learn the file formats and codec settings for optimizing quality and media bandwidth and apply them in developing a basic media player application. Learning Goals: After completing this course, you will be able to: 1. Explain the tradeoffs between media quality and bandwidth for content delivery. 2. Extract and display metadata from media files. 3. Implement and demonstrate a simple media player application using DragonBoard™ 410c.

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Codecs

In this module our esteemed Professor Harinath Garudadri will talk about coders and decoders (Codecs). This will allow us to make better use of our multimedia choices when working with the DragonBoardTM 410c. We want to look at the motivation behind using Codecs, the different ways to take advantage of redundancies when using codecs and finally the ability to take advantage of different receiver / transmitter combinations. If we are able to understand the way that information is sent and received over the data plane we can create and use the right codecs.

Introduction to Lesson 10:57

A Generic Model12:29

Audio Processing7:28

Image Processing6:59

Video Processing6:41

Quality Evaluation6:52

Conheça os instrutores

Harinath Garudadri
Associate Research Scientist
Qualcomm Institute of Calit2, UC, San Diego
Ganz Chockalingam
Principal Engineer
Qualcomm Institute of Calit2, UC, San Diego

Once we put all of these different tools together to

address the data rate, either for transmission, or for

retrieval, you end up with many many choices, right?

And as we saw in the miracle 13 dB demo and the JPEG images,

the signal to noise ratio does not always tell the truth.

So we need to have some way of controlling the quality.

So for the wide band audio from what we saw before, you can deduce from,

you can get certain result in data rates of about 8-12 kbps.

And for CD quality audio, you can have anywhere

from 64-256 kbps in one of the newer

AEC codecs even at 128 or 192, you have gone

beyond CD quality what people call real transparent quality.

[COUGH] Then for still images,

you can get anywhere from 30 to 300,

I think should have been kilobytes not megabytes.

I have an error here.

Based on what quality you use for your JPEG compression.

And similarly for about 412 to 1 kbps so

five megabits per second you can a very decent video quality for

streaming over the internet and the resultant data size depends on

the content itself to a large extent.

If you have Talking Heads, you can get much better accomplishing ratio,

as opposed to Federer and Jokovich playing tennis.

Then, there's lots of motions, and sometimes motion breaks.

You need to send more ifibs.

On the audio side, [COUGH] the quality evaluation

tends to be a lot more tricky than the that we used for speech.

So now you are having, asking more

pertinent questions that relate to the transparency of the signal.

And for one part you need real expert listeners who have had

many years of training in order to evaluate the codex.

And one of the testing paradigms is ABX.

You're told A is original, and B is either

encoded or B is definitely not B encoded and decoded.

And, you're given a third segment.

Your task is to see if X is very close to A, or very close to B.

So, sometimes it will be the original, sometimes it will be the encoded.

And the other one is ABC HR.

HR stands for hidden reference.

A and B are the original and decoded in random order.

And C is always the original.

So you have to actually Identify which is the process signal and

then assign a subjective scope.

In this course, are usually 0.5 scale.

[COUGH] And some of the ITU,

International Telecommunications Union, they're this tester define.

They allow fractional values so

that you cover a much bigger scale.

MUSHRA is multiple stimuli with hidden reference and anchor.

So in this test, you have a lot more content that the subjects are looking at.

And you have three or four candidate codex and you throw in codex for

which we already know the quality like g.726, g.711, or

for very high quality codex some of the g.722,

3's that runs at much higher pitching.

And the task of the users, usually you have

multiple sets of listeners that listen to this.

And it's almost an art implementing and running these tests.

So it's a very, very time consuming and elaborate process,

but they have to go through all of these when they release

the new version of mp3 codec, AAC codec, surround sound,

HE-AAC which has the sub-band application.

Well, I didn't talk about that in the technology, so let's leave that.

So, there is always a need for

a subjective tool to kind of quickly assess,

especially during the algorithm development, and

one of the notable ones for this objective quality measurement is peak.

Perceptual evaluation of audio quality.

And this branch of research is almost a science by itself because

you take the original signal and you take the process signal, and you implement

the cyte acoustics just the way some recordings do.

And you extract various sets of features and combinations and outcomes,

and MOV, this is an acronym for Model Output Variables.

Then you put them all together and come up with a grade,

and we have used this tool in my work in the past.

And, as a first cut, it's very very good.

It takes us through the initial experimentation

as we are trying to select a specific codec, specific data rate, or

a new codec algorithms, and there's some commercial versions, and

there's an University version that are free on the internet.

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