Lecture 7: Video PDF

Lecture 7: Video © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Overview – Learning outcomes: At the end of this lecture, you should be able to: Know how to use digital video Know how video works Understand digital video containers Familiar with obt...

Lecture 7: Video © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Overview – Learning outcomes: At the end of this lecture, you should be able to: Know how to use digital video Know how video works Understand digital video containers Familiar with obtaining video clips Know the concept of shooting and editing video © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Revision….Audio (sound) Q1: Sound pressure level / volume / loudness is measure in what?. Decibels (Db) Frequency of sound  Hz or KHz ultrasound Q2: Sound above audible range of hearing _____________ infrasound and sound below audible range of hearing _____________ © 2011 The McGraw-Hill Companies, Inc. All rights reserved © 2011 The McGraw-Hill Companies, Inc. All rights reserved © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Revision….Audio (sound) Q3: Process cutting the top and bottom of the wave if it clipping above and below interval level _________ Q4: Process of converting the sample amplitude to bits of quantization data ____________ Clipping may distort the sound and quantization may produce unwanted sound (hissing sound) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Video Video is an excellent tool for delivering multimedia. Video places the highest performance demands on a computer and its memory and storage. Digital video has replaced analog as the method of choice for making and delivering video for multimedia. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Understand how Video Works… Light reflected from an object through the camera’s lens is converted into an electronic signal by a 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. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Analog video transfer methods – Component video separates color and brightness over three cables. – S-video separates color and brightness over two wires. – Composite video transmits the whole video signal in a single cable. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Analog video – Video is recorded onto magnetic tapes. – Video frames are interlaced. – Interlaced video is a technique of doubling the perceived frame rate introduced with the signal used with analog television without consuming extra bandwidth. Since the interlaced signal contains the two fields of a video frame captured at two different times, it enhances motion perception to the viewer and reduces flicker by taking advantage of the persistence of vision effect. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) File size = frame size x frame rate x color depth x time Where:  frame size = image size (width x height in pixels)  frame rate = frames per second  color depth = measured in bytes  time = time in seconds Quality directly related to frame size, image size and colour depth. Quality also depends on content. Motion picture needs higher frame rate Please estimate a file size of 30 seconds commercial video (1280x720 11 pixel, 30fps, 16 bits of color) in megabytes. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Analog display standards – National Television Standards Committee (NTSC). These standards define a method for encoding information into an electronic signal that creates a television picture. It has a screen resolution of 525 horizontal scan lines and a scan rate of 30 frames per second. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  NTSC - NTSC is based on a 525-line, 60 fields/30 frames-per-second, at 60Hz system for transmission and display of video images. - This is an interlaced system in which each frame is scanned in two fields of 262 lines, which is then combined to display a frame of video with 525 scan lines. - NTSC is the official analog video standard in the U.S., Canada, Mexico, some parts of Central and South America, Japan, Taiwan, and Korea. 13 © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Analog display standards (continued) – Phase Alternate Line (PAL) PAL has a screen resolution of 625 horizontal lines and a scan rate of 25 frames per second. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  PAL - PAL is the dominant format in the World for analog television broadcasting and video display and is based on a 625 line, 50 field/25 frames a second, 50HZ system. - The signal is interlaced, like NTSC into two fields, composed of 312 lines each. - Several distinguishing features are:  better overall picture than NTSC because of the increased amount of scan lines  since color was part of the standard from the beginning, color consistency between stations and TVs are much better - There is a down side to PAL however, since there are fewer frames (25) displayed per second, sometimes we can notice a slight flicker in the image 15 © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Analog display standards (continued) – Sequential Color and Memory (SECAM). 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. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  SECAM - The SECAM (Sequential Couleur Avec Memoire or Sequential Colour with Memory) standard was introduced in the early 1960's and implemented in France. - SECAM is the "outlaw" of analog video standards. Like PAL, it is a 625 line, 50 field/25 frame per second interlaced system, but the color component is implemented differently than in either PAL or NTSC. - Countries on the SECAM system include France, Russia, Eastern Europe, and some parts of the Middle East 17 © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Digital video – The output is digitized by the camera into a sequence of single frames. – The video and audio data are compressed before being written to a tape or digitally stored. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) Digital video (continued) – Multiple HDTV formats exist. Resolutions and frame rates vary. – The aspect ratio of HDTV is 16:9. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (continued) CRT and LCD displays – Interlacing and progressive scan technologies Most computer video output is greater than 1024 x 768. – Overscan and safe title area Every analog TV displays differently. Editing systems use action safe and title safe overlays. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (interlacing) When lines 1, 3, 5, 7 ,9, etc. off your video image (from top to bottom) are draw first, its are in top field (or odd) dominance. (see basic figures below) When 2,4,6,8,etc. are drawn first, they are in bottom (or even) field dominance. 'Dominance' meaning that this 'field' is drawn first. 21 © 2011 The McGraw-Hill Companies, Inc. All rights reserved  How Video Works (progressive) - Non-interlaced video (also called progressive scan) displays video by drawing it on the screen in a single pass from top to bottom. - If working with digital video (for computer displays), then we won’t have to worry about field settings. - Computers display video on a monitor as a sequence of complete frames (non-interlaced). So, video formats designed for computers 22 don’t use fields. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Digital Video Containers Digital video architecture – Consists of a format for encoding and playing back video files by a computer. – Includes a player that can recognize and play files created for that format. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Digital Video Containers (continued) Codecs – The algorithm used to compress (code) a video for delivery. – 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. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Digital Video Containers (continued) Codecs (continued) – example of codec – MPEG is a real-time video compression algorithm. – MPEG-4 includes numerous multimedia capabilities and is a preferred standard. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Digital Video Containers (continued) Video format converters – Produce more than one version of your video to ensure that video will play on all the devices and in all the browsers necessary for your project’s distribution. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Digital Video Containers (continued) Video format converters © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Obtaining Video Clips New footage or stock footage? Training projects © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video Shooting platform – A steady shooting platform should always be used. – Use an external microphone. – Know the features of your camera and software. – Decide on the aspect ratio up front. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Storyboarding – Successful video production requires planning. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Lighting – Always strive for adequate lighting. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Chroma keys – Blue screen or chroma key editing is used to superimpose subjects over different backgrounds. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Composition – Consider the delivery medium when composing shots. – Use close-up and medium shots when possible. – Move the subject, not the lens. – Beware of backlighting. – Adjust the white balance. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Titles and text (continued) – Use plain, sans serif fonts that are easy to read. – Choose colors wisely. – Provide ample space. – Leave titles on screen long enough so that they can be read. – Keep it simple. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Titles and text (continued) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Titles and text (continued) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) 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. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Linear editing Linear video editing  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. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Nonlinear editing Non-linear video editing  uses software that allows you to arrange shots and audio on a timeline in which editing does not have to be done in the same sequence as the final video. – High-end software has a steep learning curve. Adobe’s Premiere, Apple’s Final Cut, Avid’s Media Composer – Simple editing software is free with the operating system. Microsoft’s Windows Live Movie Maker, Apple’s iMovie. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Nonlinear editing (continued) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Shooting and Editing Video (continued) Nonlinear editing (continued) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Video Compression Lossless Compression: o Preserves the exact image throughout the compression and decompression process. E.g: text images is to identify repeating words and assign them a code. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Video Compression (continued) Lossy Compression: o Eliminates some of the data in the image and therefore provides greater compression ratios than lossless compression. o Applied to video because some drop in the quality is not noticeable in moving images. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Video Compression (continued) Flavors of file formats brand to choose: o Microsoft’s AVI format o QuickTime o MPEG o Div-X o Wmv (Windows Media Video) © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Summary A digital video method is used for making and delivering video for multimedia. A charge-coupled device (CCD) converts the light that has been reflected from an object through the camera’s lens. © 2011 The McGraw-Hill Companies, Inc. All rights reserved  Summary (continued) Codecs are used to compress (code) a video for delivery and decompress a video for playback. There are many sources for digital video, but getting the rights can be difficult, time- consuming, and expensive Most video editing is now being done on computers using nonlinear editing (NLE) software such as Avid, Premiere, and Final Cut. © 2011 The McGraw-Hill Companies, Inc. All rights reserved