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.