video data topic 4: multimedia technology. learning objectives hardware required to capture digital...
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Video Data
Topic 4: Multimedia Technology
Learning Objectives
• Hardware required to capture Digital video
• How video files are stored
• Factors affecting video quality and filesize
• Features of video editing software
• Hardware required to output Digital video
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 lots of images (frames) fast
Input (Capture):Digital Video Camera (Camcorders)
Input (Capture): Webcam
• Designed for the purpose of creating videos to be transmitted over the Internet (eg Skype)
• 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
• Now often built into laptops and smartphones
Video Data:Storage of Video data
Topic 4: Multimedia Technology:
AVI (Audio Video Interleave)
• Type of RIFF file (container file)
• Uncompressed
• The audio is embedded into the video
• Lossy compression cuts out unnecessary parts of a video clip
• Saves each frame of video as a JPEG– These are called ‘i-frames’ or ‘key 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
Video Quality And File Size
• Colour depth: – Increasing colour depth improves quality and
increases file size.
• 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.
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:Output Hardware
Topic 4: Multimedia Technology:
Output hardware• As mentioned in the topic on bitmap graphics,
the graphics card is responsible for the output of image data.
• Graphics cards have become much more powerful (driven mainly by the games market) and any modern graphics card should be able to comfortably decode and display full quality videos on a computer.