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

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 DA B C DB D C AB 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.