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Chapter 7-Video

Chapter 7-Video. Objectives. Consider the implications of using digital video in multimedia. Discuss video recording and how it relates to multimedia production. Prepare digital video and images for conversion to television. Prepare for shooting and editing video for use in multimedia.

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Chapter 7-Video

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  1. Chapter 7-Video

  2. Objectives • Consider the implications of using digital video in multimedia. • Discuss video recording and how it relates to multimedia production. • Prepare digital video and images for conversion to television. • Prepare for shooting and editing video for use in multimedia. • Select the best video recording formats for your multimedia project. • Begin preparing video for the Web and CD-ROM.

  3. Overview • Concept of video • How video works? • Analog video • Digital video • Video digitizing • Shooting and editing video • Optimizing video files for CD-ROM • Broadcast video standards

  4. Concept of Video • Video is an excellent tool for delivering multimedia. • Video places the highest performance demand on computer and its memory and storage. • Digital video has replaced analog as the method of choice for making and delivering video for multimedia.

  5. Concept of Video • Digital video device produces excellent finished products at a fraction of the cost of analog. • Digital video eliminates the image-degrading analog-to-digital conversion. • Many digital video sources exist, but getting the rights can be difficult, time-consuming, and expensive.

  6. How Video Works • Light reflected from an object through the camera’s lens is converted into electronic signal by charge-coupled device (CCD). • This electronic signal contains three channels of color information and synchronization pulses (sync). • Several video standards exist that deal with the amount of separation between the components of the signal.

  7. Analog Video • Video information that is stored using television video signals, film, videotape or other non-computer media • Each frame is represented by a fluctuating voltage signal known as an analogue wave form or composite video.

  8. Analog Video • Composite analogue video has all the video components: • brightness, colour and synchronization • Then combined into one signal for delivery • Example : traditional television • Problems: colour blending, low clarity, high generation lost, difficult to edit. DIGITAL ANALOGUE

  9. Analog Video Video color: • Television sets use composite input. Hence colors are less pure and less accurate than computers using RGB component. • NTSC television uses a limited color palette and restricted luminance (brightness) levels and black levels. • Some colors generated by a computer that display fine on a RGB monitor may be illegal for display on a NTSC TV. • While producing a multimedia project, consider whether it will be played on a RGB monitor or a conventional television set.

  10. Analog Video Interlacing effects: • In television, the electron beam makes two passes on the screen while drawing a single video frame. • It first lays down all the odd-numbered lines, and then all the even-numbered lines, hence they are interlaced. • While capturing images from a video signal, they can be filtered through a de-interlacing filter provided by image-editing applications.

  11. Analog Video Text and titles for television and taking care of analog tapes: • Titles for video productions can be created with an analog character generator. • Computers can create titles digitally using video and image-editing software. • New tapes should always be fast-forwarded to the end and then rewound, to ensure even tape tension.

  12. Digital video is the digitisation of analogue video signals into numerical format It creates the illusion of full motion by displaying a rapid sequence of changing images on a display device. Conversion from analogue to digital format requires the use on an ADC (Analogue to Digital Converter) A Digital to Analogue Converter (DAC) can be used to output digital video on analogue equipment Digital Video

  13. Digital Video • Video clip stored on any mass-storage device can be played back on a computer’s monitor without special hardware. • Setting up a production environment for making digital video, requires some hardware specifications. • Some specifications include computer with FireWire connection and cables, fast processor, plenty of RAM, fast and big hard disk.

  14. VCR Video Digitizing • Digital video is often used to capture content from movies and television to be used in multimedia. • A video source (video camera ,VCR, TV or videodisc) is connected to a video capture card in a computer. • As the video source is played, the analog signal is sent to the video card and converted into a digital file (including sound from the video). Video Overlay Board / Video Capture Card • PC

  15. Video Digitizing Analogue signal from VCR Converted to DIGITAL by VIDEO CAPTURE CARD The converted signal is entered inside a computer Signal is processed Video is edited using video editing software software

  16. Digital Video Architecture • Digital video architecture consists of a format for encoding and playing back video files by a computer. • Architecture includes a player that can recognize and play files created for that format.

  17. FULL VIDEO Taken from the CD into memory buffer DISPLAY ON SCREEN MEMORY BUFFER Digital Video Compression • Digital video compression schemes or codecs is the algorithm used to compress (code) a video for delivery. • The codec then decodes the compressed video in real-time for fast playback. • Streaming audio and video starts playback as soon as enough data has transferred to the user’s computer to sustain this playback.

  18. Compresses when saved CODEC File format used such as: Avi, Mpeg, Mov Decompresses when needed for display Digital Video Compression • The video compression/decompression programs are used so that video can fit on a single CD and the speed of transferring video from a CD to the computer can be increased. • Let us say that a sequence of 25fps video is about 25MB. • CD-ROM transfer rate is calculated as follows: • 1X= 150KB per second • 10X=1.5 MB per second • 100X= 15 MB per second

  19. Digital Video Compression • Two types of COMPRESSION: • Lossless compression • Preserves the exact image throughout the compression and decompression process. E.g: text images is to identify repeating words and assign them a code.

  20. Digital Video Compression • Lossy compression • Eliminates some of the data in the image and therefore provides greater compression ratios than lossless compression. • Applied to video because some drop in the quality is not noticeable in moving images.

  21. Digital Video Compression • Two types of CODEC (lossy): • Spatial compression • a digital compression of video data that compresses the size of the video file by compressing the image data of each frame • Compression is done by removing redundancy from data in the same frame.

  22. Digital Video Compression • Temporal compression • a digital compression of video data that uses similarities of sequential frames over time to determine and store only the image data that differs from frame to frame. • Compression is done by removing similarity between successive video frames

  23. Digital Video Compression • Flavors of file formats brand to choose: • Microsoft’s AVI format • QuickTime • MPEG • Div-X • Wmv (Windows Media Video)

  24. Digital Video Compression • Standards have been established for compression programs, including JPEG (Joint Photographic Experts Group) and MPEG (Motion Picture Experts Group).

  25. JPEG (Spatial) • Often areas of an image (especially backgrounds) contain similar information. • JPEG compression identifies these area and stores them as blocks of pixels instead of pixel by pixel reducing the amount of information needed to store the image. • These program reduce the file size of graphic images by eliminating redundant information.

  26. MPEG (Temporal) • The changes in the image from frame to frame. • Key frames are identified every few frames the changes that occur from key frame. • Provide greater compression ratios than JPEG. • Initially, it requires extra hardware for multimedia.

  27. MPEG (Temporal) MPEG is a real-time video compression algorithm. MPEG-4 includes numerous multimedia capabilities and is a preferred standard. MPEG-7 (or Multimedia Content Description Interface) integrates information about motion video elements with their use.

  28. File Size and Formats • There is an important consideration: • file size in digitized video which included • frame rate • image size • color depth.

  29. File Size and Formats • Frame Rate • animation is an illusion caused by the rapid display of still images. • television and movies play at 30 fps but acceptable playback can be achieved with 15 fps.

  30. File Size and Formats • Image Size • A standard full screen resolution is 640x480 pixels but to safe storing space a video with 320x240 for a computer display is still acceptable. • New high-definition televisions (HDTV) are capable of resolutions up to 1920×1080p60, • 1920 pixels per scan line by 1080 scan lines, progressive, at 60 frames per second.

  31. File Size and Formats • Color Depth • The quality of video is dependent on the color quality (related to the number of colors) for each bitmap in the frame sequence.

  32. File Size and Formats • The color depth below 256 colors is poorer-quality image. • The frame rate to below 15 fps causes a noticeable and distracting jerkiness that unacceptable. • Changing the image size and compressing the file therefore become primary ways of reducing file size. 24 bit 16 bit 8 bit (256 colors)

  33. Optimizing Video Files for CD-ROM • CD-ROMs provide an excellent distribution medium for computer-based video. • When preparing video for CD-ROM distribution, interleave the audio track(s) with the video track. • Key frames should be used every 10 to 15 frames and the size of the video window must be kept small. • The Sorenson codec is optimized for CD-ROM playback.

  34. Broadcast Video Standards National Television Standards Committee (NTSC): These standards define a method for encoding information into electronic signal that creates a television picture. It has screen resolution of 525 horizontal scan lines and a scan rate of 30 frames per second.

  35. Broadcast Video Standards Phase Alternate Line (PAL) and Sequential Color and Memory (SECAM): PAL has a screen resolution of 625 horizontal lines and a scan rate of 25 frames per second. SECAM has a screen resolution of 625 horizontal lines and is a 50 Hz system. SECAM differs from NTSC and PAL color systems in its basic technology and broadcast method.

  36. Broadcast Video Standards Advanced Television Systems Committee (ATSC) Digital Television (DTV): This digital standard provides TV stations with sufficient bandwidth to present four or five Standard Television (STV) signals or one High Definition TV (HDTV) signal. This standard allows for transmission of data to computers and for new Advanced TV (ATV) interactive services.

  37. Shooting and Editing Video • Import video and sound at the highest resolution and with the least amount of compression possible. • Resolution should be reduced and footage must be compressed later according to the requirements. • A steady shooting platform should always be used.

  38. Shooting and Editing Video • Good and even lighting is extremely important. • Blue screen in digital video editing applications is a popular technique for making multimedia. • Wide panoramic shots and camera motion should be avoided when shooting for a small computer window on CD-ROM or the Web.

  39. Video Editing Terminology • Linear • It plays end to end in one direction, usually pertains to videotape editing specifically the editing of linear tape segments into one final master tape.

  40. Video Editing Terminology • Non-linear • Refers to the editing of disk-based digital video. • The software provides an on screen map of what the final video sequences should look like incorporating the edits, splices, special effects, transitions and sound tracks.

  41. Special Effects • Transitions • Such as fading, wiping, splatters, scrolling, stipple and many more are available by simply dragging and dropping that transition between the two video clips.

  42. Special Effects • Superimposing • The ability to superimpose one clip over another is a valuable technique. • The technique of green screening is identical except that the color green is used for the screen and later digitally removed. • The blue screen and green screen superimposing are just two of the superimposing technique available.

  43. Special Effects • Digital video editing applications provide special effect filters to create lens flares and emboss, tint, pan, twist and zoom the video image. • These special effects can often be set up to change over the duration of the video clip.

  44. Summary • Digital video method is used for making and delivering video for multimedia. • Compression techniques help to reduce the file sizes to more manageable levels • Two types of compression lossless and lossy. • Standards for compression program are JPEG and MPEG.

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