1. Video Data Topic 4: Multimedia Technology

2. 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)

3. 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)

5. 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

6. 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

7. Video Data: Storage of Video data Topic 4: Multimedia Technology:

8. 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.

9. 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

11. 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

12. Video Quality And File Size Colour depth: –Increasing colour depth improves quality and increases 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’.

13. 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.

14. Calculations File Size (Bytes) = Frame Size ( resolution * colour depth) x Frame Rate (fps) x Video Time (s)

15. Calculations Uncompressed AVI Frame Rate 24 fps Frame Size 320 x 240 pixels Duration 9s Colour Depth 16 bits per pixel (R*CD) * (fps*L) File Size = 1.8mb (320 * 240 * 16) * (24*9)

16. Video Data: Video Editing Topic 4: Multimedia Technology:

17. 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

18. Simple plan of final product Usually freehand and rough Important process for all multimedia applications Produced at Analysis stage Storyboards

19. Basically, cutting or removing the parts you don’t want. You may want to remove a frame or a whole scene. Crop

20. 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

21. Transitions Used to ‘join up’ different scenes/frames Different types are available, for example: Wipe

22. Transitions Used to ‘join up’ different scenes/frames Different types are available, for example: Dissolve

23. Transitions Used to ‘join up’ different scenes/frames Different types are available, for example: Box Out

24. Transitions Used to ‘join up’ different scenes/frames Different types are available, for example: Fade