Lecture 8: DIGITAL VIDEO technology

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LECTURE 8:DIGITAL VIDEO TECHNOLOGYEVI INDRIASARI MANSOREmail: [email protected]

Tel ext: 1741

Outline Using video How video works? Broadcast video standards Analog video Digital video Video recording and tape formats Video editing technology Optimizing video files for CD-ROM

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Learning Outcomes Summarize the implications of using digital video in

multimedia Illustrate video recording and its relation to multimedia

production Prepare digital video and images for conversion to

television

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Using video4

Video is an excellent for delivering multimedia Video places the highest performance demand on

computer and its memory and storage Digital video has replaced analog as the method of

choice for making and delivering video for multimedia

Using video (cont)5

Digital video device produces excellent finished products at a fraction of the cost of analog

Digital video eliminates the image-degrading analog-to-digital conversion

Many digital video sources exist, but getting the rights can be difficult, time-consuming, and expensive

How video works6

Light reflected from an object through the camera’s lens is converted into electronic signal by charge-coupled device (CCD)

This electronic signal contains three channels of color information and synchronization pulses (sync)

Several video standards exist that deal with the amount of separation between the components of the signal

How video works (cont)7

Broadcast video standards8

National Television Standards Committee (NTSC): These standards define a method for encoding

information into electronic signal that creates a television picture

It has screen resolution of 525 horizontal scan lines and a scan rate of 29.97 frames per second

Broadcast video standards (cont)9

Phase Alternate Line (PAL) and Sequential Color and Memory (SECAM): PAL has a screen resolution of 625 horizontal lines

and a scan rate of 25 frames per second SECAM has a screen resolution of 625 horizontal

lines and is a 50 Hz system SECAM differs from NTSC and PAL color systems in

its basic technology and broadcast method

Your TV

Each frame is a single picture When played rapidly one after another, it gives the illusion of motion Everybody

knows that, right?

Take NTSC as an example: The overall signal has 525 lines (only 480 are actually visible, the extra 45 gives the TV time to reset the

electronic beam to the top of the screen) A single frame is ‘painted’ on the screen in an INTERLACED fashion (line-by-line)

Firstly: Odd-numbered lines (i.e. 1,3,5, …, 479) – takes ~1/60 seconds Then: Even-numbered lines (i.e. 2,4,6, …, 480) – takes ~1/60 seconds

You might notice after this seeing 480i (or 525i). This means 480-interlaced! [Later you’ll see 480p? Apa itu?]

BTW, all the above is called Standard Definition TV – Digital TV format which is 480i

Your TV ... As it gets bigger

When screens get bigger, scan lines during interlacing become visible. This produces ‘jaggedies’… No body likes ‘jaggedies’… (19” vs 60” example)

Solution: PROGRESSIVE SCANNING!!! ALL the lines from 1-480 are ‘painted’ on the screen at just

one single pass!!! Feasible with today’s technology since coding and transfer

speeds have dramatically improved This called for a new name… Henceforth – Enhanced

Definition TV was born [more of a marketing gimmick though… but hey, who really cares?]

480p, 525p

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EDTV’s advantage Most TVs cannot handle 480p

And what if we’re still getting interlaced signals? Won’t a progressive scan system be a waste, then?

EDTV can take interlaced signals, and pass them through a DEINTERLACER/LINE-DOUBLER 1st: All the odd and even numbered scan lines are

combined. This also improves smoother (‘jaggedies’ are smoothed out) 525i is converted to 480p here BTW, all of this is also done @ 1/60 second

2nd: The next 1/60 is used to feed the frame a second time! Increases brightness and stability of the frame Eliminates or reduces jaggedies, giving a cleaner picture

HDTV (High Definition TV) What HDTV does?

1. Increases number of scan lines 2. Widens aspect ration from 4:3 to 16:9 (baru la mcm wayang sikit,

ye dok?) Well.. That’s basically it… Comes with the same variation

1080i – interlaced. However, since there are so many lines, the jaggedies aren’t that visible (illusion of better quality!)

1080p – progressive scanning… but, do you really need it? … You yourself will be the decider (bionic eyes vs. normal human eyes)

Marketing hype however, will tell you otherwise Full HD – max resolution possible (1920X1080) HD-ready – Meaning ure non-HD TV can be connected to an

HD external box if you want to received HD signals HD – Takes the full HD signal and resizes it down a bit

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HDTV (High Definition TV) Alternatively, the 720-lines progressive

scan or 720p is also available However, some interlacing artifacts might

still be visible at 1080i Therefore, video with rapid motion would

not be suitable at 1080i, and would be nicer to view @ 720p

For drama swasta (soap operas), 1080i would be nice

SDTV, EDTV and HDTV side-by-side

The different TV resolutions

Analog video17

Video information that is stored using television video signals, film, videotape or other non-computer media

Each frame is represented by a fluctuating voltage signal known as an analogue wave form or composite video

Analog video (cont)18

Composite analogue video has all the video components: brightness, colour and synchronization Then combined into one signal for delivery

Example : traditional television Problems: colour blending, low clarity, high generation

lost, difficult to edit


Video color: Television sets use composite input. Hence colors are

less pure and less accurate than computers using RGB component

NTSC television uses a limited color palette and restricted luminance (brightness) levels and black levels.

Some colors generated by a computer that display fine on a RGB monitor may be illegal for display on a NTSC TV.

While producing a multimedia project, consider whether it will be played on a RGB

monitor or a conventional television set.


Interlacing effects: In television, the electron beam makes two passes on

the screen while drawing a single video frame It first lays down all the odd-numbered lines, and then

all the even-numbered lines, hence they are interlaced

While capturing images from a video signal, they can be filtered through a de-interlacing filter provided by image-editing applications


Text and titles for television and taking care of analog tapes: Titles for video productions can be created with an

analog character generator. Computers can create titles digitally using video and

image-editing software. New tapes should always be fast-forwarded to the

end and then rewound, to ensure even tape tension.

Digital video22

Video clip stored on any mass-storage device can be played back on a computer’s monitor without special hardware

Setting up a production environment for making digital video, requires some hardware specifications

Some specifications include computer with FireWire connection and cables, fast processor, plenty of RAM, fast and big hard disk

Digital video (cont)23

Digital video architecture Digital video architecture consists of a format for

encoding and playing back video files by a computer Architecture includes a player that can recognize and

play files created for that format


Digital video compression Digital video compression schemes or codecs is the

algorithm used to compress (code) a video for delivery

The codec then decodes the compressed video in real-time for fast playback

Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback


Digital video compression (cont) MPEG is a real-time video compression algorithm MPEG-4 includes numerous multimedia capabilities

and is a preferred standard MPEG-7 (or Multimedia Content Description Interface)

integrates information about motion video elements with their use [NOT A COMPRESSION STANDARD]


Digital video compression (cont) The video compression/decompression programs are

used so that video can fit on a single CD and the speed of transferring video from a CD to the computer can be increased

Let us say that a sequence of 25fps video is about 25MB

CD-ROM transfer rate is calculated as follows: 1X= 150KB per second 10X=1.5 MB per second 100X= 15 MB per second

To overcome large video size, CODECS were developed


Compresses when saved

CODEC

File format used such as: Avi, Mpeg, MovDecompresses

when needed for display

Digital video compression (cont)


Digital video compression (cont) Digital video compression schemes or codecs is the

algorithm used to compress (code) a video for delivery

The codec then decodes the compressed video in real-time for fast playback

Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback

FULL VIDEO Taken from the CD

into memory bufferDISPLAY ON SCREEN

MEMORY BUFFER


Digital video compression (cont) Two types of COMPRESSION:

Lossless compression preserves the exact image throughout the

compression and decompression process e.g.,: text images is to identify repeating words

and assign them a code


Digital video compression (cont) Lossy compression

Eliminates some of the data in the image and therefore provides greater compression ratios than lossless compression

Applied to video because some drop in the quality is not noticeable in moving images


Digital video compression (cont) Two types of CODEC (lossy):

Spatial compression Digital compression of video data that

compresses the size of the video file by compressing the image data of each frame

Compression is done by removing redundancy from data in the same frame


Digital video compression (cont) Temporal compression

Digital compression of video data that uses similarities of sequential frames over time to determine and store only the image data that differs from frame to frame

Compression is done by removing similarity between successive video frames


Digital video compression (cont) Flavors of file formats brand to choose:

Microsoft’s AVI format QuickTime MPEG Div-X Wmv (Windows Media Video)

http://images.google.com/imgres?imgurl=www.premiereforms.com/images/links/quicktime.gif&imgrefurl=http://www.premiereforms.com/links.html&h=156&w=145&prev=/images?q=QuickTime&svnum=10&hl=en&lr=&ie=UTF-8&sa=G


Digital video compression (cont) Standards have been established for compression

programs, including JPEG (Joint Photographic Experts Group) and MPEG (Motion Picture Experts Group)


Digital video compression (cont) JPEG (spatial)

Often areas of an image (especially backgrounds) contain similar information

JPEG compression identifies these area and stores them as blocks of pixels instead of pixel by pixel reducing the amount of information needed to store the image

These program reduce the file size of graphic images by eliminating redundant information


Digital video compression (cont) MPEG (temporal)

The changes in the image from frame to frame Key frames are identified every few frames the

changes that occur from key frame Provide greater compression ratios than JPEG Initially, it requires extra hardware for multimedia


Digital video compression (cont) MPEG (temporal) – (cont)

MPEG – real-time video compression algorithmMPEG-4 includes numerous multimedia capabilities

and is a preferred standardMPEG-7 (or Multimedia Content Description Interface) integrates information about motion video elements with their use

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MPEG compression

On how MPEG compression works, please view these videos http://www.youtube.com/watch?v=kyztYavfFMs http://www.youtube.com/watch?

v=P7abyWT4dss Skip the technical (maths) parts in the

second video, instead focus on the concept of how things are done

Video recording and tape formats40

File size and formats There is an important consideration:

File size in digitized video which included 1. Frame rate2. Image size3. Color depth

Video recording and tape formats (cont)41

File size and formats (cont) Frame Rate

animation is an illusion caused by the rapid display of still images.

television and movies play at 30 fps but acceptable playback can be achieved with 15 fps

[Show VirtualDub Example]


File size and formats (cont) Image Size

A standard full screen resolution is 640x480 pixels but to safe storing space a video with 320x240 for a computer display is still acceptable

New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080 , p60,

1920 pixels per scan line by 1080 scan lines, progressive, at 60 frames per second

http://en.wikipedia.org/wiki/High-definition_television


File size and formats (cont) Color Depth

The quality of video is dependent on the color quality (related to the number of colors) for each bitmap in the frame sequence


File size and formats (cont) The color depth below 256 colors is poorer-quality

image The frame rate to below 15 fps causes a noticeable

and distracting jerkiness that unacceptable Changing the image size and compressing the file

therefore become primary ways of reducing file size

24 bit 8 bit (256 colors)16 bit

Video Compression

• Digitizing full-motion video in the computer requires transfer of ENORMOUS amounts of data in a short period of time

• Consider this:

Frame rate = 25 fps (FR) Color depth of each frame = 65,536 colors (thus a bit depth of 16-bits) (BD) Frame size = 320 X 240 pixel dimension (D)

• FORMULA FOR VIDEO SIZE (per second) = FR X BD X D• For this particular video… the UNCOMPRESSED video would be:

25 X 16 X (320 X 240) 30,720,000 bits / second 3.67 Mbytes / second

• This is just for 1-SECOND!!! And we’re not even talking about AUDIO yet • A 1-hour video would thus be 3.67 X 60 X 60 = 13,212 Mbytes• Which is equals to = 12.9 Gigabytes … Now… try fitting that onto a CD

Video Compression

• A simpler example with less big numbers

• Consider this:

Frame rate = 2 fps … meaning, in every second of the video, TWO pictures are being displayed continuously (FR)

Color depth of each frame = 4 colors (thus a bit depth of 2-bits) … meaning that each frame of the video has a maximum of 4 colors (BD)

Frame size = 320 X 240 pixel dimension … each frame’s size (D)

• FORMULA FOR VIDEO SIZE (per second) = FR X BD X D• For this particular video… the UNCOMPRESSED video would be:

2 X 4 X (320 X 240) 614,400 bits / second 0.073 Mbytes / second 614,400 / 8 / 1024 / 1024

• As you can see… this rate is very2 acceptable due to the small data rate • BUT! Your video is going to be very2 UN-colorful :P If there exists such a word…• Not to mention it being very2 flicker-y…

Video about compression48

• The basics of Video Compression• MPEG video• Codecs and Containers (formats) – 1• Codecs and Containers (formats) – 2

Video editing technology 49

Linear It plays end to end in one direction, usually pertains to

videotape editing specifically the editing of linear tape segments into one final master tape

Video editing technology (cont)50

Non-Linear Refers to the editing of disk-based digital video. The software provides an on screen map of what the

final video sequences should look like incorporating the edits, splices, special effects, transitions and sound tracks.


Special effects Transitions

Such as fading, wiping, splatters, scrolling, stipple and many more are available by simply dragging and dropping that transition between the two video clips


Special effects (cont) Superimposing

The ability to superimpose one clip over another is a valuable technique

The technique of green screening is identical except that the color green is used for the screen and later digitally removed

The blue screen and green screen superimposing are just two of the superimposing technique available

Video editing technology53

Superimposing


Video digitizing Digital video is often used to capture content from

movies and television to be used in multimedia A video source (video camera ,VCR, TV or videodisc)

is connected to a video capture card in a computer As the video source is played, the analog signal is

sent to the video card and converted into a digital file (including sound from the video)


VCR

Video Overlay Board /

Video Capture Card

PC

Video digitizing (cont) http://alfiantroxion.blogspot.com/2010/06/tv-

capture-card-101-macam-mana-nak.html

http://www.cnn.com/2000/TECH/computing/09/20/vcr.graphics.card.idg/story.pc.tv.jpg


Video digitizing (cont)

Analogue signal from VCRConverted to DIGITALby VIDEO CAPTURE CARD

The converted signal isentered inside a computer

Signal is processedVideo is edited using video editing software software


Video editing software Incorporating transitions such as dissolves, wipes and

spin Superimposing titles and animating them, such as fly-

in logo Applying special effects to various images, such as twisting, zooming, rotating and distorting Synchronizing sound with the video Apply filters that control color balance, brightness &

contrast, blurring, distortions and morphing

Advantage of using video58

Captures interest Increase retention Clarifies complex physical actions and relationships Can incorporate other media

Disadvantage of using video59

Is expensive to produce Requires extensive memory and storage Requires special equipment Does not effectively illustrate abstract concepts and

static situations

Shooting and editing video60

Import video and sound at the highest resolution and with the least amount of compression possible

Resolution should be reduced and footage must be compressed later according to the requirements

A steady shooting platform should always be used

Shooting and editing video (cont)61

Good and even lighting is extremely important Blue screen in digital video editing applications is a

popular technique for making multimedia Wide panoramic shots and camera motion should be

avoided when shooting for a small computer window on CD-ROM or the Web

Optimizing video files for CD-ROM

CD-ROMs provide an excellent distribution medium for computer-based video

When preparing video for CD-ROM distribution, interleave the audio track(s) with the video track

Key frames should be used every 10 to 15 frames and the size of the video window must be kept small

The Sorenson codec is optimized for CD-ROM playback

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Summary Digital video method is used for making and delivering

video for multimedia Compression techniques help to reduce the file sizes to

more manageable levels Two types of compression lossless and lossy Standards for compression program are JPEG and

MPEG

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Lecture 8: DIGITAL VIDEO technology

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