Video

Table of Content 1.Introduction 2.Types of video signal 3.Types of analog video signal 4.Computer-based digital video 5.Broadcast and video standards 6.Characteristics of digital video 7.Digital video data sizing 8.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.Luminance 2.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 در هم تابيدن يا Interlace پرتو الكترون در رسم يك فريم ويديو، دو گذر انجام مي‌دهد :  ابتدا تمام خطوط فرد و سپس خطوط زوج ترسيم مي‌شود.

NTSC ايالت متحده و كانادا و مكزيك و ژاپن و... دقت صفحه( خطوط پيمايش ) : 525 خط افقي 30 فريم در ثانيه 60 HZ Interlace Aspect Ratio = 4:3

PAL بريتانيا، اروپاي غربي، استراليا، آفريقاي شمالي، چين، آمريكاي شمالي و ايران و... دقت صفحه ( خطوط پيمايش ) : 625 خط افقي 25 فريم در ثانيه 50 HZ Interlace Aspect Ratio = 4:3

SECAM فرانسه، اروپاي شرقي، شوروي سابق و... دقت صفحه ( خطوط پيمايش ) : 625 خط افقي 25 فريم در ثانيه 50 HZ Interlace Aspect Ratio = 4:3

HDTV High Definition Television Aspect Ratio = 16: X 720

رنگ ويديو نمايش و بازتاب رنگ بين مانيتورهاي تلويزيوني و كامپيوتري متفاوت است. چون كامپيوترها از مولفه RGB استفاده مي‌كنند و رنگ‌ها خالص‌تر و دقيق‌تر است. تلويزيون از جعبه رنگ محدود و سطوح لومينانس و سطوح سياه محدود استفاده مي‌كند. بعضي از رنگ‌هاي توليد شده توسط كامپيوتر د تلويزيون نامعتبر است.

متن و عناوين در تلويزيون فونت‌هاي عناوين بايد ساده، بدون اضافات و به اندازه كافي پررنگ باشد. وقتي متن را در پس زمينه تيره قرار مي‌دهيد، از رنگ سفيد يا روشن براي متن استفاده كنيد. حروف را به هم نچسبانيد. از رنگ‌هاي خيلي گرم استفاده نكنيد. عناوين را به آهستگي نمايش دهيد. شدت رنگ‌هاي همجوار كاملاً بايد متفاوت باشد.

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 * T Where 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 Hz x 8-bit/8 x 2) = 184,320, ,000 bytes = 185,202,000 bytes

Ways to reduce video file size  Reduce the size of the playback window - Internet 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 از codec  الگوريتمي براي فشرده‌سازي ويديو براي تحويل و سپس رمزگشايي آن در زمان بي‌درنگ براي اجراي سريع.  الگوريتم‌هاي فشرده‌سازي ويديوي بي‌درنگ :  MPEG  Indeo ……

MPEG  MPEG-1  استاندارد فشرده‌سازي ويديو براي سي‌دي  1.2 Mbps video & 250 Kbps stereo audio  MPEG2  استاندارد فشرده‌سازي ويديو براي دي‌وي‌دي و تلويزيون ديجيتال  3-5 Mbps video & Multi Channel audio &...  MPEG-4  روش مبتني بر محتوا، قابليت اجراي واقعيت مجازي، تنظيم شدن با سرعت‌هاي مختلف دانلود  MPEG-7  واسط توصيف محتواي چندرسانه‌اي  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

Summary 1.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)