DIGITAL VIDEO By: Jose Martinez

WHAT IS DIGITAL VIDEO? Refers to the capturing, manipulation and storage of video in digital formats. A digital video camcorder, for example, is a video camera that captures and stores images on a digital medium such as a SD card. Digital A/V information consists of discrete units of data that are placed so close together that the human senses perceive them as a continuous flow. Before digital video everything was done with analog video.

HISTORY -Video production equipment that were digital in their internal workings started to show up around the late 1970s to early 1980s, such as TBC and DVE. The way these work is by taking in analog video and digitizing it so it could be enhanced and then later converted back to analog. -DVE - Digital video effects are visual effects that provide comprehensive video image manipulation. They deal primarily with resizing, distortion or movement of the image.

HISTORY TBC - Time base correctors were used to eliminate errors caused by mechanical instability present in analog recordings. - Time base correction counteracts errors by buffering the video signal and releasing it at a steady rate.

THOMSON-CSF 9100 DIGITAL VIDEO PROCESSOR(TBC) AND AMPEX ADO(DVE)

HISTORY Not long after well known companies began to develop prototypes of digital videotape recorders, but none were marketed commercially. Digital video was not introduced commercially until 1986 when Sony released the Sony D-1 and later introduced the Sony D-2. Both were expensive, but D-2 was more successful, because D-1 had a connection with three cables and the D-2 had one cable to and from the VCR. Both recorded uncompressed digital form.

D-2 VCRD-1 VCR

HISTORY Eventually they were replaced by cheaper systems that used video compression such as, Sony Betacam, Sony Betacam SX, Ampex’s DCT and Panasonic’s DVCPRO. In 1990 one of the first digital video products to run on personal computers was PACo which could stream unlimited-length video with synchronized sound from a single file on a CD- Rom.

HISTORY In 1991 Quicktime, Apple Computers architecture for time- based and streaming data formats appeared. It was low quality and required an analog video source to be digitized to a computer-readable format using external equipment. In 1992 Bernard Luskin and Eric Doctorow successfully put the first fifty videos in digital MPEG 1format on CD, and were able to launch the movies on CD. Standard playback was introduced such as MPEG-1 and MPEG-2, which were used for DVD media.

HISTORY Digital video tape format was also introduced making it possible for recordings to be transferred directly to digital data, simplifying the editing process, and allowed non-linear editing systems to be deployed cheaply and widely on desktop computers, without the requirement of external equipment. These advancements lead to where we are today. Digital video is used by millions of individuals daily through a variety of devices.

FRAME RATE/BIT RATE -Digital video has a series of orthogonal bitmap digital images displayed in rapid succession at a constant rate. -These are called frames and are measured by frames per second. -Pixels are small areas of light on the screen and they have only one property, their color. The color of a pixel is represented by a fixed number of bits. The more bits the more subtle variations of colors can be reproduced. This is called the color depth of the video.

FRAME RATE/BIT RATE In interlaced video the frame is in two halves(fields). 10framesps = 20fieldsps One half contains the even numbered lines and the second half contains the odd numbered lines that are captured at different times. This enhances the motion perception to the viewer and reduces flicker.

FRAME RATE/BIT RATE Bit rate happens to be very important. It measures the information of the digital video stream. In order for a video transmission to work the transmission link must be capable of supporting that bit rate. Storage space for the video is also determined by the bit rate along with the duration of the video. Uncompressed videos bit rate is too high for most applications and video compression is needed.

FRAME RATE/BIT RATE Pixels per frame = W(pixels) * L(pixels) Bits per frame = pixels per frame * Color depth Bit rate = bits per second * frames per second Video size = bit rate * length of video in seconds When dealing with uncompressed video the video size will be a large amount of space.

COMPRESSION Digital video files can be very large. For example a video with a frame size of 640x480 at a color depth of 24 bits and frame rate of 25fps running for ten minutes would take almost 14 GB to store if uncompressed. Using compression would reduce the file size by eliminating unnecessary data for reconstruction purposes. There are two types of compression, lossless and lossy.

COMPRESSION In lossy compression, image and sound information that won’t be noticed by the viewers will be removed. Information is lost during this process, but human perception wont tell the difference and the quality perceived is still the same. Another method used is Chroma subsampling. This takes advantage of the fact that the human eye perceives spatial changes of brightness more sharply than those of color, by averaging or dropping some of the chrominance(color information of picture) information in the image. The luma signal is responsible for the information about the brightness of the picture.

COMPRESSION Lossless compression keeps the original data so that the individual image sequences remain the same. It decreases space by removing image areas that use the same color. Less desirable, because of the low compression rate compared to the high compression rate of the lossy method.

Lossless compression allows original data to be perfectly reconstructed(low compression rate). Lossy compression removes data(high compression rate).

COMPRESSION A well known compression format is MPEG(Moving Picture Experts Group). MPEG uses lossy compression to achieve a high compression rate by only storing the changes from one frame to another. There are three types of MPEG. MPEG-1 provided a 352x240 resolution at 30 fps, which was no better than VCR video.

COMPRESSION MPEG-2 provides 720x480 and 1280x720 resolutions at 60 fps. This is commonly used for DVDs. MPEG-4 is very useful for video recorded to flash memory and online distribution of large videos. There is no MPEG-3, but there are other compression methods, such as AVI and MOV.

ADVANTAGES -Being able to manipulate the video is a huge advantage. Many effects are now easily achieved by bringing in files from Photoshop, Flash, and Sound Edit as components in a video mix. -Another Advantage is the preservation of data. It is much easier to maintain the quality of a digital video. Traditional tapes are subject to wear and tear more than DVD or hard drive.

ADVANTAGES Digital video can be copied over and over without any information being lost. When dealing with analog signals it can easily be distorted and will lose much of its data after a few transfers. A digital video is easy to store and send via the internet to multiple users without having to make a copy for every viewer.(Ex: streaming) Digital video costs significantly less than the former methods.

POPULARITY Digital video is now used in mobile phones, tablets, personal computers, etc.(Youtube, Skype, Netflix) and because, of that reason it is becoming more popular than ever before. Users are streaming, downloading and uploading video on a daily basis. Even with all the digital video usage of today, TV is still the more popular of the two mediums. Each passing year TV usage is decreasing and the digital video usage has been increasing. This is because, TV viewers are starting to rely on other means to keep up with the shows they watch.

POPULARITY

REFERENCES online-video-in-5-charts/ online-video-in-5-charts/ Ang, Tom Digital Video Handbook. London: Dorling Kindersley. Digital Video: An Introduction to MPEG-2 By Barry G. Haskell, Atul Puri, Arun N. Netravali Also used google to obtain various photos. DTV: The Revolution in Digital Video 3rd Edition by Jerry Whitaker

THE END