video data topic 4: multimedia technology. what is video? a video is just a collection of bit-mapped...
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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
• 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
Uncompressed AVI
Frame Rate 24 fps
Frame Size 320 x 240 pixels
Duration 9s
Colour Depth 16 bits per pixel
Duration 9s
File Size =
Video Data:Storage of Video data
Topic 4: Multimedia Technology
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
Timeline
• Simple plan of final product
• Usually freehand and rough
• Important process for all multimedia applications
• Produced at Analysis stage
Storyboards
• Basically, cutting or removing the parts you don’t want.
• You may want to remove a frame or a whole scene.
Crop
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
Video Data:Video Editing
Topic 4: Multimedia Technology: