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What Bandwidth Does DVD & HDTV Quality Video Need?

Many claim to be able to deliver on-demand video,  but IT's the quality and speed that counts.

At InfoTelesys, we believe consumers are not prepared to accept quality that is lower than that which they are already accustomed to.

TV has set the standard.  Postage stamp, jerky video is the best you can achieve on 56kbps modems or DSL.  What you can deliver over the old Internet simply won't meet consumer expectations.  You need full screen DVD quality and HDTV media, you need IT-I2™.

Don't be fooled, its all in the Pixels.

Digital video is made up of pixels, the little dots on your screen.  Each pixel on a color monitor has a Red, a Green and a Blue element.  To show true color, that is the number of colors the eye is capable of seeing, you need 8 bits for each color, or 24 bits per pixel.  If you are doing any fancy graphics such as those used in computer games, you may use 32 bits per pixel for special effects.

How Many Pixels In That Window?  
How many bites does it take
to make a pretty picture?

The quick bandwidth calculation you can do at home if you own a computer with a DVD drive.

  1. Take a DVD movie, place it in your DVD drive on your computer.
  2. Open the file manager (Explorer) and right click on the DVD drive to report how much disk space is being used.
  3. Divide the amount of disk space used (usually 4,000 Megabytes - 4GB) by the length of the movie in hours. (Typical feature length movies are two hours)
4,000 / 2 = 2 Gigabytes per Hour
4,000 / 120 = 33.33 MB per min.
Divide by 60 for MB per sec.
33.33 / 6 = 0.555 Mbytes/sec
Multiply by 8 to convert from Bytes to Bits
0.555 * 8 = 4.44 Mbps (Mbits / sec)
Add approx. 40% for protocol overhead
4.44 * 1.4 = 6 Mbps

i.e. You will need a network connection of 6 Mbps to play the movie you have on your computer. HDTV quality video needs 24 Mbps!

Typical monitor resolutions have 28 pixels per centimeter (72 pixels "dots" per inch).  In other words, there are approximately 28 x 28 pixels, or 784 pixels for each square centimeter of your screen.  Simple math tells us 784 x 24 bits = 18,816 bits.  18.8Kbits, or 2.3Kbytes, is what one square centimeter of your screen takes to show a true color picture.  To get an idea of how much bandwidth would be required at true color without any compression,  the following chart does the math for us:
Screen Resolution: VGA SVGA XVGA SXVGA
Horizontal Pixels 640 800 1024 1280
Vertical Pixels 480 600 768 1024
Total # Pixels 307,200 480,000 786,432 1,310,720
Total # Bits at 24 Bit Color 7,372,800 11,520,000 18,874,368 31,457,280
Megabytes at 24 Bit color 0.9 1.4 2.4 3.9
Mega bits per second at 30 frames per second 221.18 345.60 566.23 943.72

When you realize the enormous volume necessary to deliver smooth video, you understand the need for compression:


Compression Throws Away Pixels

The simple fact is that for any photograph, compression throws away pixels, and consequently picture quality and resolution.  There are many different compression techniques available for still pictures.  However, there are basically only two compression techniques that are broadly supported, gif and jpeg.  It is not much use having a proprietary compression technique, when nobody can view the picture - a bit like saying that the English language is not that efficient, so from today we will use the Funny galore language.

Still, frame compression uses different techniques to compress the picture.  The basic approach is to split the picture into regions, then find out if the same color is represented in a particular region and share the pixels for that region.  Different compression techniques yield different results:

Bitmap Image
1,087.9 KB
Jpeg - Higher Quality Image
17.9 KB
Gif Image
11.1 KB
Jpeg - Lower Quality Image
1.14 KB
We'll spare you the download and send just a small section of the picture:

Clearly in the Jpeg - Lower Quality Image example, we have gone too far with the compression and far too much quality is lost.  Picture size is not the only issue. 

Quality DVD

DVD video uses highly advanced compression to cut the volume of data not only the still frames, but from frame to frame.  DVD uses MPEG 2 (Moving Picture Exchange Group 2) compression.  MPEG first of all compresses the individual picture frames, then transmits only the changes in the picture from frame to frame with an index frame transmitting the whole picture every now and then.  For example, if the camera was fixed on the tiger example above, the background and much of the tiger would remain the same, only the mouth of the tiger changes as it yawns.  Only the pixels that change around the mouth region are transmitted in the next frame.  Remember to achieve smooth motion you need to send around 30 frames (pictures) for every second of video.

MPEG 2,  the mainstay of video compression, does a great job compressing video.  MPEG 4 is essentially the same, with some interactive features.  Considering that the uncompressed VGA stream at 221 Mbs is compressed down to 6 Mbps to only 3% of it's original size, MPEG 2 does a great job.  However, the ability to compress a video is largely dependant on the type of video.   If we are shooting steady shots without much movement from a fixed camera, we can achieve large compression rates while maintaining reasonable quality.  However, if we are shooting fast moving action from a hand held camera, such as the generation-X type movies, then the ability to compress the video stream and maintain quality is eliminated.

6 Mbps Now, What About The Future?

Video and movies today are tending towards faster action and shorter frames, eliminating our ability to maintain quality and high compression.  Ten years ago, the typical movie shot lasted three seconds, today most generation-X shots are one second.

IT's quite simple, consider if a pixel region on the video changes from one frame to the next - if the video moves fast and it does change, then you need to transmit a new pixel color to replace the old one.

Bandwidth requirements for DVD quality video and up, start at 6 Megabits per second and go higher. Soon we will probably well exceed the 24 Megabit bandwidth requirement of HDTV, particularly as we move into the virtual reality world where we use 32 bit or even 64 bit planes.

The Bottom Line

"The bottom line is that those who claim to deliver quality on-demand video over regular Internet, need their pixels read." CLive.  IT's simple math, you need a 6 Mbps pipe just to get into the quality game, and that's ignoring the enormous I/O (input and output) requirements and multimedia standards support.

Consider 50 million homes watching DVD quality video on-demand in the U.S. alone.  That's 300,000,000 Megabits per second bandwidth, or three hundred thousand fiber optic cables all equipped with the latest technology out of the labs, supporting a Terabit per second per fiber.  And that's not even considering if Dad wants to watch a different movie to Son or Daughter, let alone Mum's choice.  What about the rest of the world, let's not forget China and India, why should they too not receive the same quality service.

InfoTelesys' way is the only way to deliver on-demand, high quality video, we are building the bandwidth to handle the enormous I/O.  We support the multimedia standards.  InfoTelesys' IT-IT™ can deliver well into the Petabite bandwidth range, even well into and beyond the Exabit bandwidth range.

This is IT™, InfoTelesys, The Next Internet™.


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