IS502:M ULTIMEDIA D ESIGN FOR I NFORMATION S YSTEM F UNDAMENTAL CONCEPTS IN VIDEO Presenter Name: Mahmood A.Moneim Supervised By: Prof. Hesham A.Hefny Winter 2012

Video Video has become an important feature of the Internet after the development of digital video (DV) technology and higher network speeds A digital camcorder records video on a tape using one of the following formats: mini-DV, DVCAM or DVCPRO, and connect to the computer by a FireWire Interface Some camcorders have an internal hard disk, while others write directly to DVDs By Mahmood A.Moneim2

Video Standard DV camcorders or VTRs connected to computers over FireWire are used for reasonable quality digital video capture Cheap video cameras are often built into mobile phones and laptop computers or used as Webcams. They usually use MPEG-4 and USB 2.0 Digital video standards inherit features from analogue broadcast TV: 1.National Television Systems Committee (NTSC) standard Used in the US, Japan, South America 2.Phase Alternating Line (PAL) standard Used in Western Europe, Middle East, China 3.Sequential Couleur avec Memoire (SECAM) standard Used in France, Eastern Europe and Russia By Mahmood A.Moneim3

Video Standard By Mahmood A.Moneim4

Video Standards Television sets were traditionally based on Cathode Ray Tubes (CRTs) Raster scanning principle: The screen is divided into horizontal lines. Electron beams sweep across the screen tracing each line and moving down to trace the next The picture we see is built up from top to bottom as a sequence of horizontal lines The screen has to be refreshed 40 times/sec to avoid flickering By Mahmood A.Moneim5

Video Standards By Mahmood A.Moneim6

Video Standards Transmitting an entire picture that many times a second requires large bandwidth Therefore, each frame is divided into two fields (odd and even lines), transmitted one after the other and interlaced for display Persistence of vision will help not noticing that at any moment, only half the image is displayed By Mahmood A.Moneim7

Video Standards Interlaced frames may display combing when displayed progressively or exported as still images By Mahmood A.Moneim8

Video Standards Originally, the rate at which frames were transmitted was chosen to match the local AC line frequency: a field rate of 50 per second in Western Europe and 60 per second in North America A field rate of 50 per second corresponds to 25 frames/sec (because of interlacing) PAL: a frame has 625 lines, of which 576 are picture, displayed at 50 fields (25 frames) per second (625/50) NTSC: a frame has 525 lines, of which 480 are picture, displayed at fields (29.97 frames) per second (525/59.94, often treated as 525/60) By Mahmood A.Moneim9

Digital video Standards Since digital video will be displayed on the same screens used for traditional video, back compatibility is required The standard often used to sample video to convert it to digital form is the CCIR 601 standard A video frame has to be sampled in both directions: - In vertical direction, 576 lines for PAL and 480 lines for NTSC - CCIR 601 uses 720 lines for horizontal sampling regardless of the scanning standard Therefore, PAL frames are 720 × 576 and NTSC are 720 × 480 By Mahmood A.Moneim10

Digital Video Standard CCIR 601 uses the YCBCR color space where Y corresponds to luminance, CB is Y – Blue and CR is Y – Red It is used with 4:2:2 chrominance sub-sampling Since the human eye is less sensitive to variations in color than to variations in brightness, fewer color samples are needed compared to luminance samples By Mahmood A.Moneim11

Digital Video Standards DV applies 4:1:1 chrominance sub-sampling and compresses to a constant data rate of 25 Mbits per second, a compression ratio of 5:1 High quality DVPRO and Digital-S formats use the 4:2:2 sampling MPEG defines a series of standards. MPEG-2 is used on DVDs; MPEG-4 supports a range of multimedia data at bit rates from 10 kbps to 300 Mbps or greater MPEG-4 defines a file format. 3GP is a simpler version, used in mobile phones By Mahmood A.Moneim12

Digital Video Standards High Definition (HD) represents any format that has larger frames than the standard formats HD video uses higher resolutions and may be progressively scanned. Frames with widths of 720 and 1080 pixels and an aspect ratio of 16:9 are used HD frames are either progressively scanned or interlaced. If progressive scanning is used, the letter “p” is written after the frame rate. If interlacing is used, the letter “i“ is written By Mahmood A.Moneim13

Digital Video Standards Example: HD of i indicates a frame of size 1920 x 1080 interlaced at 60 fields per second Comparison of different formats By Mahmood A.Moneim14

Editing and post production Video editing is the process of constructing a complete movie from a set of video clips or scenes, combining them with sound where required By Mahmood A.Moneim15

Editing and Post-Production Post-production is concerned with making changes or compositing the material, using operations that are similar to bitmapped image manipulations Traditional films used to be edited by physically cutting frames from the film and splice them together to compose a scene By Mahmood A.Moneim16

Editing and Post-Production Effects such as dissolves and wipes are more complicated to do in traditional films. They required the use of a device called an optical printer Such device uses two projectors, each projecting the films that are to be dissolved onto a camera. Filters are used for each projector to control the dissolve effect By Mahmood A.Moneim17

Editing and Post-Production Digital video editing made editing much easier similar to how typing in a word processor on a computer is compared to using a typewriter During editing, clips are imported, trimmed and assembled on a timeline. Transitions, such as dissolves, may be added between overlapping clips By Mahmood A.Moneim18

Editing and Post--Production Edited digital video can be played back as soon as it’s edited not like how it used to be with traditional films In post-production, the values of effects’ parameters may vary over time By Mahmood A.Moneim19

Video Delivery Video may be delivered over a network as a downloaded file, it may be streamed or it may be delivered by progressive download Embedded video: The video is transferred from a server to the user’s machine and not played back until the entire file has arrived Progressive download (HTTP streaming): The file starts playing as soon as enough of it has arrived In true streaming, the video is never stored on the user’s disk, but it does require sufficient bandwidth to deliver frames fast enough to be played By Mahmood A.Moneim20

Video Delivery Example (Progressive Download): Consider a 30-second movie that has been compressed to a data rate of 2Mbps (Every second of the movie is saved in 2Mb) If the movie to be sent over a connection operating at 512 kbps, the movie will take 30 sec x 2Mbps/512kbps = 120 seconds to download After 90 seconds, three-quarters of the frames will have been received. So, if the movie starts playing at that point, by the time the 90 seconds are done, the rest of the movie would arrive By Mahmood A.Moneim21

Multimedia Architecture A multimedia architecture provides: - An API (Application programming interface) for capture, playback and compression; - A container format for storing media data - A streaming server - Software tools, such as a player QuickTime and DirectShow are the multimedia architectures included with Mac OS X and Windows, respectively. Their file formats are MOV and WMV Flash Video is widely used for Web video. FLV files must be played in the Flash Player with a SWF that controls the video playback (or in a third-party player) By Mahmood A.Moneim22

Q UESTIONS ? By Mahmood A.Moneim23