Video

Table of Content

1. Introduction2. Types of video signal3. Types of analog video signal4. Computer-based digital video5. Broadcast and video standards6. Characteristics of digital video7. Digital video data sizing8. Ways to reduce video file size 9. Video file formats

Definition of Video

• Video:• Technology of electronically

• Capturing / recording (captured media)• Processing / storing• Transmitting a sequence of still images representing scenes in motion.

Note: • Animation starts from discrete pictures and then process to

illusion of continuous motion.• Discrete pictures illusion of continuous motion

Types of Video signal

• Two types of Video Signal• Analog video• Digital video

Analog Video Signal

• Analog video is transferred by analog signal.

• It contains the • luminance (brightness) and • chrominance (colour) of the image.

• Most TV still sent and received video as an analog signal.

Types of Analog Video Signal

• Three types of Analog Video Signal:

• Component

• Composite

• S-Video

Component Video

• Signals are split into 2 or more components; separates the:• Luminance: brightness (Y)• Chroma: colours (U and v)

Component Video

Advantage: Gives the best colour reproduction, since no “crosstalk” between the three different channels, unlike composite video and S-video.Disadvantages: Requires more bandwidth and good synchronization of the three components.

Composite Video

• Composite video = two or more signals are mixed into a single carrier wave.

Chroma (colours ) UV and Luminance (Brightness) Y = YUV

• Video quality not as good as component video.

Composite Video

S-Video

• S-Video = separates into 2 signals :1. Luminance2. Chroma

• S-Video is also known as Separate Video or Y/C. • Y Luminance Brightness• C Chroma Colour

• The chroma or colour information is always combined into 1 signal.

• Video quality better than composite video, worse than component video.

S-Video

Aspect ratio

• Aspect Ratio: ratio of the screen width to the screen height.

The aspect ratio of current television tubes is 4/3.

For wide-screen television tubes the aspect ratio is 16/9

Digital Video Signal

• Digital video is transferred by digital signal.

• In most multimedia applications, the video signals need to be in a digital form in order to• store them in the memory of a computer and • to easily edit and integrate them with other

media types.

Computer-based digital video

Three significant advantages: It can be copied and reproduced without loss of quality It can be manipulated easily – repositioned, resized, and

recolor by a computer It is easier to transmit over computer networks.

Three disadvantages: It requires an enormous amount of computer storage space. It requires high transfer rates. Large file sizes and high transfer rates required for quality

digital video, so the majority of the digital video currently available has made compromises that produce images lower in quality than those on VHS tapes.

Broadcast and Video Standards

• NTSC

• PAL

• SECAM

• HDTV

Interlace

Interlaceدر هم تابيدن يا

پرتو الكترون در رسم يك فريم ويديو، دو گذر •

انجام مي دهد :

ابتدا تمام خطوط فرد و سپس خطوط زوج ترسيم

مي شود.

NTSC

ايالت متحده و كانادا و مكزيك و ژاپن و ...•

خط افقي525) : خطوط پيمايشدقت صفحه(•

فريم در ثانيه30•

•60 HZ

•Interlace

•Aspect Ratio = 4:3

PAL

بريتانيا، اروپاي غربي، استراليا، آفريقاي شمالي، •

چين، آمريكاي شمالي و ايران و ...

خط افقي625 : )خطوط پيمايش(دقت صفحه•

فريم در ثانيه25•

•50 HZ

•Interlace

•Aspect Ratio = 4:3

SECAM

فرانسه، اروپاي شرقي، شوروي سابق و ...•

خط افقي625 : )خطوط پيمايش(دقت صفحه•

فريم در ثانيه25•

•50 HZ

•Interlace

•Aspect Ratio = 4:3

HDTV

•High Definition Television

•Aspect Ratio = 16:9

•1280 X 720

رنگ ويديو

نمايش و بازتاب رنگ بين مانيتورهاي تلويزيوني و كامپيوتري •

استفاده RGBمتفاوت است. چون كامپيوترها از مولفه

مي كنند و رنگ ها خالص تر و دقيق تر است.

تلويزيون از جعبه رنگ محدود و سطوح لومينانس و سطوح •

سياه محدود استفاده مي كند.

بعضي از رنگ هاي توليد شده توسط كامپيوتر د تلويزيون •

نامعتبر است.

متن و عناوين در تلويزيون

فونت هاي عناوين بايد ساده، بدون اضافات و به اندازه كافي •

پررنگ باشد.

وقتي متن را در پس زمينه تيره قرار مي دهيد، از رنگ سفيد •

يا روشن براي متن استفاده كنيد.

حروف را به هم نچسبانيد.•

از رنگ هاي خيلي گرم استفاده نكنيد.•

عناوين را به آهستگي نمايش دهيد.•

� بايد متفاوت باشد.• شدت رنگ هاي همجوار كامًال

Characteristics of digital video

A frame single image in a video sequence.

The frame is the basic feature of digital video: height width color depth. (color resolution)

Characteristics of digital video

Frame rate the number of images displayed

within a specified amount of time to convey a sense of motion.

Frame rate per second.

Characteristics of digital video

Frame size The VGA standard - monitors with resolutions

of 640 x 480 pixels. Need high image storage and processing

power so usually frame sizes are less than 640 x 480 pixels.

Common frame sizes : 640 x 480 for full screen VGA display 320 x 240 quarter of a VGA display 240 x 180 about a sixth of a VGA display 160 x 120 sixteenth of a VGA display

Characteristics of digital video

Color depth or resolution

• refers to the number of colors displayed on the screen at one time.

1 bit for 2 colors to 8 bits/pixel (256 colors), 16 bits/pixel (65, 535 colors), and 24 bits/pixel (16.7 million colors).

Digital video data sizing

• Digital video file size ( in bytes)= F * C * R * TWhere• F = frame size (width x height)• C= colour depth (in bytes)• R= frame rate (frames per second)• T= time in seconds

Calculate Video File Size (Example 1)• Duration=10 mins• Frame rate=25 fps• Frame size=160 by 120• Colour resolution=8-bit

Video file size=600 sec x 25 fps x 160 x 120 x (8-bit/8)

= 288,000,000 bytes = 288 MB

Calculate Video File Size (Example 2)• Duration=10 sec• Frame rate=30 fps• Frame size=VGA• Colour resolution=2 bytes

• Sampling rate/Frequency=44.1 kHz• Sound resolution=8-bit• Channel=Stereo

Video File Size:(10 sec x 30 fps x 640 x 480 x 2 bytes) + (10 sec x 44100 Hz x 8-bit/8 x 2)= 184,320,000 + 882,000 bytes= 185,202,000 bytes

Ways to reduce video file size

Reduce the size of the playback window - Internet - 160 x 120 pixels.

Decrease the number of colors, from 16 million to 256 or even 16 colors.

Reduce the frame rate from 30 down to 15 or less frames per second but more jerky.

Compress the file.

فشرده سازي ويديوي ديجيتال

استفاده ازcodec الگوريتمي براي فشرده سازي ويديو براي تحويل و سپس رمزگشايي

آن در زمان بي درنگ براي اجراي سريع.

: الگوريتم هاي فشرده سازي ويديوي بي درنگMPEGIndeo…

MPEG

MPEG-1 استاندارد فشرده سازي ويديو براي سي دي 1.2 Mbps video & 250 Kbps stereo audio

MPEG2 استاندارد فشرده سازي ويديو براي دي وي دي و تلويزيون ديجيتال 3-5 Mbps video & Multi Channel audio & . . .

MPEG-4 روش مبتني بر محتوا، قابليت اجراي واقعيت مجازي،

تنظيم شدن با سرعت هاي مختلف دانلود

MPEG-7 واسط توصيف محتواي چندرسانه اي توانايي جست و جوي سريع آرشيوهاي ويديو

Video file formats MPEG – most popular format MOV – the Quicktime format(standard for

Macintosh) AVI – the MS- Windows RealVideo - streaming

Summary1. Video is the technology of electronically capturing,

processing, and transmitting a sequence of still images representing scenes in motion.

2. 2 types of video signal: Analog video, Digital video

3. 3 types of analog video signal: Component, Composite, S-Video

4. Broadcast and video standards: NTSC, PAL, SECAM, HDTV

Summary

5. Video size =

(Time(in sec)*Frame rate*Frame size*Colour resolution(in byte))

+

(Time(in sec)*Frequency(in Hz)*Sound resolution(in byte)*Channel)