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Mm Unit 4

Mm Unit 4






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    Mm Unit 4 Mm Unit 4 Presentation Transcript

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