Video Data

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. Input (Capture):Digital Video Camera (Camcorders) • 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

4. 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

5. 25 - 30 years ago

6. 20 - 25 years ago

7. 10 – 20 years ago

8. More recently

9. Input (Capture):Digital Video Camera (Camcorders)

10. 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

11. 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

12. 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.

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

14. 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.

15. MPEG • 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

16. MPEG

17. MPEG Standards • 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

18. 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’.

19. 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 MPEG4 compression reduces file sizes without unduly affecting quality.

20. Calculations File Size (Bytes) = Frame Size (Bytes) x Frame Rate (fps) x Video Time (s)

21. Calculations

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

23. Timeline • 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

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

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

26. BDCA ABCD 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

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

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

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

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

31. Video Data:Output Hardware Topic 4: Multimedia Technology:

32. Output hardware • As mentioned in the topic on bitmap graphics, the graphics card is responsible for the output of image data. • Due to the complex codecs and high bit-rates needed to output video data, • video output cards used to be needed in order for a computer to be able to display videos at full quality. • 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.

33. Digital to Analogue Converter (DAC) • As most people have analogue displays (LCD displays with digital (DVI) inputs are available) graphics cards must be able to generate the analogue signals needed for the monitors. • The DAC changes the digital video signal in the computer into an analogue video signal that the monitor can use to display the image.

34. Digital Signal Processor • The Digital Signal Processor (or GPU) plays a key role in allowing computer to display full-quality videos. • The GPU on the graphics card is responsible for decoding the video signal • Takes the pressure off the CPU