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Lecture 3: Video

LECTURE 8 THE USES OF DIGITAL VIDEO IN MULTIMEDIA. Lecture 3: Video. Objective. Analogue video What is digital video? Calculating the size of digital video Compression techniques Digital video formats Video capture hardware Digital video editing Consumer desktop video. Analogue video.

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Lecture 3: Video

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  1. LECTURE 8THE USES OF DIGITAL VIDEO IN MULTIMEDIA Lecture 3: Video

  2. Objective • Analogue video • What is digital video? • Calculating the size of digital video • Compression techniques • Digital video formats • Video capture hardware • Digital video editing • Consumer desktop video

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

  4. Analog video • Usage : television • Problems: colour blending, low clarity, high generation lost, difficult to edit

  5. Type of Analogue Video Signal • There are two main analogue video formats • PAL and NTSC • PAL (Phase Alternate Line) • standard television format used in the European, UK, Australia and South Africa • Consist 625 scan lines drawn every 1/25 second

  6. Type of Analogue Video Signal • NTSC is the American and Japanese standard • Consist of 525 scan lines drawn every 1/30 second • Television usually has a 4:3 aspect ratio • For every 1 pixel down there are 1.333 pixels across • Aspect ration is the comparison of width to height for a viewing area • Digital TV has an aspect ratio of 16:9 (wide screen)

  7. What is digital video? • Digital video is the digitisation of analogue video signals into numerical format • It creates the illusion of full motion by displaying a rapid sequence of changing images on a display device. • Conversion from analogue to digital format requires the use on an ADC (Analogue to Digital Converter) • A Digital to Analogue Converter (DAC) can be used to output digital video on analogue equipment

  8. Video capture Technology and Playback Systems The lecture for this part please refer note that will be given later…..

  9. Digital Video Software The lecture for this part please refer note that will be given later…..

  10. File Size Considerations • Several elements determine the file size, in additional to the length of the video. These including: • Frame rate • Number of images displayed within a specified amount of time to convey a sense of motion • Usually measured in frames per second • Standard video movie  30 fps, movie film  24 fps • Video digital  at least 15 fps

  11. File Size Considerations • Frame or Image size • the width and height of each individual frae or image • Determines the quality of the image displayed and the processing involved to display that image • Standard full screen resolution is 640x480 pixels • Video screen display is one fourth the size of the full window screen (320x240)

  12. File Size Considerations • Color depth/Resolution • Number of colors displayed on the screen at one time • Ranging from 1 bit to 8 bit, 16 or 24 bit per pixel • Quality directly related to frame size, image size and color depth. • Qualitiy also depends on content. Motion picture needs higher frame rate

  13. Calculating the sizeof digital video Where: • Frame size = image size ( width * height in pixels) • Frame rate = frames per second • Color depth = measured in bytes • time = time in seconds This does not include any sound data ! File size = frame size * frame rate * Color Depth * time

  14. Compression techniques • Since the size of raw digital video is so prohibitively large we need some means to compress the information • Video compression and decompression program, known as Codecs • Lossy compression techniques cause some information to be lost from the original image • Redundant information • Example: Image and video • JPEG and MPEG • Intraframe and Interframe

  15. Compression techniques • Lossless compression techniques do not lose information throughout the compression and decompression process • Example use in text images • Exactly same before and after compression • Technique is identify repeating words and assign them a code. • Decompression, the code would be changed back to the actual word.

  16. Digital video formats MPEG / MJPEG Files with a .mpg extension Apple QuickTime Files with a .mov or .qt extension Microsoft AVI Files with a .avi extension

  17. MPEG video • Named after the Moving Picture Experts Group who devised the compression and file formats • There are a number of MPEG formats: • MPEG-2 is used for digital TV broadcasts and DVDs • MPEG-1 is a format used for low quality video (generally displayed on computers) • MPEG-1 Layer 3 is the popular encoding mechanism for MP3 audio files (more on this later in this course) • MPEG-4 is a new format for multimedia presentations • Can require separate hardware to decode higher quality MPEG video data

  18. MPEG compression example A simple scene showing a car moving across a desert landscape Only the difference between the current and next frame needs to be stored This is called intraframe coding

  19. QuickTime • Developed by Apple, Inc. • Primarily for playback without any hardware assistance • Can achieve compression ratios of 25 to 200:1 • The QuickTime format can also store audio, graphics, 3D and text making it more much versatile for multimedia applications

  20. Microsoft AVI • Audio Video Interleave format • Interleaving is a technique used to embed two or more things into the same stream of information • In every chunk of information you will find some video data and some audio data 001001010010010101010011110101... 001001010010010101010011110101... ... 001001010010010101010011110101... 8, 16 or 24 bits Video information Audio information 001001010010010101010011110101...

  21. Digital video editing • Analogue tape editing is a linear process • To find the section you want, you may have to forward or rewind the video tape • To move a section to another place in the sequence you have to either re-record the section onto another tape or physically cut and splice the video tape

  22. Digital video editing • Digital video editing can be non-linear process • You can move sections around inside the computer and play those sections back in any order

  23. Consumer desktop video • Typified by the Apple iMac DV computer • IEEE 1394 or FireWire interface • Digital camcorders

  24. How audio can be used effectively Example of uses for video • Showing physical procedures. Some uses are: • Installing a board in a PC • Adjusting engine timing • Attracting and holding attention. Some uses are: • Advertising products and services • Teaching new skills to busy employees

  25. How audio can be used effectively • Presenting scenarios. Some uses are: • Training technicians to respond to equipment malfunctions • Demonstrating possible uses for a product • Analyzing motion . Some uses are: • Body motion to improve athletic performance • Traffic patterns for transportation planning

  26. Advantages and Disadvantages of using video Video adds visual impact to multimedia applications: • Advantages • Captures interest • Increase retention • Clarifies complex physical actions and relationships • Can incorporate other media

  27. Advantages and Disadvantages of using video • Disadvantages • Is expensive to produce • Requires extensive memory and storage • Requires special equipment • Does not effectively illustrate abstract concepts and static situations

  28. Summary • Today we have seen how analogue video formats are composed and how digital video can be used to store these electronically • Digital video demands huge file sizes • even before sound is added on! • Compression techniques help to reduce the file sizes to more manageable levels

  29. Next lecture... • We will look at how Animation can be used in multimedia applications

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