Mm Unit 4

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Mm Unit 4

  1. 1. Video Data Topic 4: Multimedia Technology
  2. 2. What is Video? <ul><li>A video is just a collection of bit-mapped images that when played quickly one after another give the illusion of a moving image </li></ul><ul><li>It is a sequence of individual pictures or frames </li></ul><ul><li>The standard rate at which these frames are taken is 25 frames per second (this gives realistic movement) </li></ul>
  3. 3. <ul><li>Work in the same way as digital cameras </li></ul><ul><li>They use the same light sensors, called CCDs </li></ul><ul><li>They have a lower resolution than cameras </li></ul><ul><li>They are designed to capture lost of images (frames) fast </li></ul>Input (Capture): Digital Video Camera (Camcorders)
  4. 4. Input (Capture): Digital Video Camera (Camcorders) <ul><li>Consumer cameras use a RGB filter which is of poorer quality than professional ones. </li></ul><ul><li>Professional cameras use 3 CCDs each one with a different colour filter: </li></ul><ul><ul><li>Red, Green & Blue </li></ul></ul>
  5. 5. Input (Capture): Digital Video Camera (Camcorders)
  6. 6. Input (Capture): Webcam <ul><li>Designed for the purpose of creating videos to be transmitted over the Internet </li></ul><ul><li>They do not need to be high resolution, keeping down the bit rates and price. </li></ul><ul><li>They use low resolution array CCDs and low quality lenses, keeping costs down </li></ul>
  7. 7. Input (Capture): Video Capture Card <ul><li>A video capture card is needed to capture videos from analogue sources </li></ul><ul><ul><li>video tape players, television broadcasts and analogue video recorders </li></ul></ul><ul><li>Some modern graphics cards include the ability to capture video </li></ul>
  8. 8. Input (Capture): Specialist Video Capture Card <ul><li>They often have faster ADCs and can capture videos at higher bit rates </li></ul><ul><li>They usually capture sound as well. </li></ul><ul><ul><li>Allows synchronisation </li></ul></ul><ul><li>Have a hardware codec </li></ul><ul><ul><li>Allowing it to be processed and stored in a compressed format as it is being captured. </li></ul></ul>
  9. 9. Video Data: Storage of Video data Topic 4: Multimedia Technology:
  10. 10. AVI (Audio Video Interleave) <ul><li>Type of RIFF file (container file) </li></ul><ul><li>Uncompressed </li></ul><ul><li>AVI ratio set during saving </li></ul><ul><ul><li>The audio is embedded into the video at different intervals. </li></ul></ul>
  11. 11. <ul><li>Lossy compression cuts out unnecessary parts of a video clip </li></ul><ul><li>Saves each frame of video as a JPEG </li></ul><ul><ul><li>These are called ‘i-frames’ </li></ul></ul><ul><li>Data that stays the same in following frames is removed </li></ul><ul><li>The next frames only store data on what has changed since last i-frame </li></ul>MPEG
  12. 12. MPEG
  13. 13. <ul><li>MPEG-1 </li></ul><ul><ul><li>VHS video quality with 353 x 240 pixels and 30 fps frame rate support </li></ul></ul><ul><li>MPEG-2 </li></ul><ul><ul><li>The standard for DVD-Video and Digital Television </li></ul></ul><ul><li>MPEG-3 </li></ul><ul><ul><li>Intended for HDTV but these revisions were incorporated into MPEG-2) </li></ul></ul><ul><li>MPEG-4 </li></ul><ul><ul><li>Designed for low-bandwidth networks - e.g. video phones) (Part used by DivX </li></ul></ul><ul><li>MPEG-7 </li></ul><ul><ul><li>Builds on the interactive and extra data capabilities of MPEG-4 and is a full multimedia description format </li></ul></ul>MPEG Standards
  14. 14. Video Quality And File Size <ul><li>Colour depth: </li></ul><ul><ul><li>Increasing colour depth improves quality and file sizes. </li></ul></ul><ul><li>Resolution: </li></ul><ul><ul><li>Increasing resolution improves quality and increases file sizes. </li></ul></ul><ul><li>Frame rate: </li></ul><ul><ul><li>Measured in frames per second (FPS). </li></ul></ul><ul><ul><li>Increasing frame rate increases file size. Lower frame rates reduce file size but make video clip ‘jerky’. </li></ul></ul>
  15. 15. Video Quality And File Size <ul><li>Video time: </li></ul><ul><ul><li>increasing or reducing the time of a video is the obvious way to affect the file size. </li></ul></ul><ul><ul><li>Quality of the display of the clip is not affected. </li></ul></ul><ul><li>Lossy compression: </li></ul><ul><ul><li>Using MP3 compression reduces file sizes without affecting quality. </li></ul></ul>
  16. 16. Calculations <ul><li>File Size (Bytes) = Frame Size (Bytes) x Frame Rate (fps) x </li></ul><ul><li>Video Time (s) </li></ul>
  17. 17. Calculations 9s Duration 16 bits per pixel Colour Depth File Size = 320 x 240 pixels Frame Size 24 fps Frame Rate Uncompressed AVI
  18. 18. Video Data: Video Editing Topic 4: Multimedia Technology:
  19. 19. <ul><li>Each frame is displayed as a thumbnail image. </li></ul><ul><li>Each frame can be individually edited </li></ul><ul><li>The audio would also be on an timeline </li></ul><ul><li>Some packages provide multiple timelines </li></ul>Timeline
  20. 20. <ul><li>Simple plan of final product </li></ul><ul><li>Usually freehand and rough </li></ul><ul><li>Important process for all multimedia applications </li></ul><ul><li>Produced at Analysis stage </li></ul>Storyboards
  21. 21. <ul><li>Basically, cutting or removing the parts you don’t want. </li></ul><ul><li>You may want to remove a frame or a whole scene. </li></ul>Crop
  22. 22. Sequencing <ul><li>Once you’ve got your video cropped, edited you have to put it in sequence. </li></ul><ul><li>In other words, put it in the correct order </li></ul>A B C D B D C A
  23. 23. Transitions <ul><li>Used to ‘join up’ different scenes/frames </li></ul><ul><li>Different types are available, for example: </li></ul><ul><ul><li>Wipe </li></ul></ul>
  24. 24. Transitions <ul><li>Used to ‘join up’ different scenes/frames </li></ul><ul><li>Different types are available, for example: </li></ul><ul><ul><li>Dissolve </li></ul></ul>
  25. 25. Transitions <ul><li>Used to ‘join up’ different scenes/frames </li></ul><ul><li>Different types are available, for example: </li></ul><ul><ul><li>Box Out </li></ul></ul>
  26. 26. Transitions <ul><li>Used to ‘join up’ different scenes/frames </li></ul><ul><li>Different types are available, for example: </li></ul><ul><ul><li>Fade </li></ul></ul>

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