The answer is technology. It's a bit of a miracle that video can be delivered at all over the web, considering the data rates. A full-quality television channel delivers 1800 pictures ("frames") per minute and each one contains perhaps a million bytes of information -- many, many times the maximum delivery rate of the highest speed modems. So delivering video via the web requires some compromises and some clever engineering.
Here is a chart comparing video media advantages and disadvantages.
| Video media | Advantages | Disadvantages |
| Broadcast television | Inexpensive, high quality | You watch whatever's on, whenever it's on |
| VHS (PAL) Tape | Inexpensive, high quality | Tape or disk needs to get to you |
| Downloaded video (internet) | On-demand: You get the video you want, when you want it | Quality is limited by compression and you have to wait for it to download |
A television picture includes a lot of redundant information -- neighbouring areas tend to be close to the same color and lightness, neighbouring frames often change little. Compression uses fancy math to avoid sending the same information again and again, compressing the data with varying amounts of image degradation and the introduction of artefacts.
Even with compression, we're still looking at a hefty load of data, so file size are still huge. No matter what, video clips eat up megabytes per minute and take a long time -- sometimes hours -- to download via modem. This is still better than shipping videotapes (especially for short clips and commercials), but still lacks the immediacy that is the calling card of the World Wide Web.
When we first decided to offer video on this website, we chose to offer two (2) file sizes, one for both bandwidths, modem and broadband links to the internet. For the standard phone 56 K modem, we recommend the 56K Dial-up Phone Modem link. For the high speed modem or video link, we recommend the High Speed LAN Multiple Bit Rate link. Each of these links are associated with a file size optimized for the speed of the link.
56K Dial-up Phone Modem link = average 500 Kilobytes video file size
High Speed LAN Multiple Bit Rate link = average 3 Megabytes video file size
|
Internet communication speed |
Time to download |
|
| Average file size | ||
|
bits per second |
500 kilobytes |
3 Megabytes |
| 9600 bits/sec | 7.11 min | 42.67 min |
| 14.4 Kilobits/sec | 4.74 min | 28.44 min |
| 28.8 Kilobits/sec | 2.37 min | 14.22 min |
| 56 Kilobits/sec | 1.22 min | 7.31 min |
| 1 Megabits/sec | 4.00 sec | 24.00 sec |
| 1.5 Megabits/sec | 2.60 sec | 15.63 sec |
The distinction between bits and bytes is important when measuring bandwidth. There are eight bits in a byte. So a 28.8 kilobit per second modem passes 28,800 bits of data per second, but only 3,600 bytes (or 3.6 kilobytes) per second.
Bandwidth is a measure of how much data can be transmitted using a given high-speed Internet technology. This amount is usually measured in kilobits per second (Kbps) or megabits per second (Mbps). The bandwidth dimension is directly proportional to the quality of the video.
A few other parameters are sacrificed to the bandwidth limitations, such as screen size, video noise, frame rate and color fidelity. The result is a good news-bad news scenario: The bad news is that the picture quality is much, much, much less than what a $4 videotape delivers. The good news is that it can happen at all! While a tape requires at least a day to deliver, an electronic clip can be delivered right away.
A normal television picture delivers 30 full pictures per second (25 for PAL systems). Most computer video cuts this down to 15 or 10 or even fewer pictures per second. Typical web-based videos also use a quarter or a sixteenth of a screen to decrease file size when downloading.
Downloading and viewing a video is pretty easy. When you click on an appropriate link, the video downloads as a file. This may take a long time, depending on the video. You then launch the file using an appropriate viewing application. If your browser is correctly configured, the viewing application launches automatically and opens the newly downloaded video.
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