Tips
Digitizing Tips and Techniques
It's easy to create digital video for your website, CD-Rom, or Powerpoint presentation. There are several variables which will affect the quality of digital video delivery which you should be aware of when digitizing. Size, frame rate, bit rate, and codec must be coordinated with your playback medium to ensure quality playback. In the following page, we will illustrate how these variables affect video playback and suggest standards which can be applied to common delivery medium.
Choosing an appropriate frame size for your movie has an important
effect on video quality. All else being equal, the higher the image size
at a given data rate, the lower the resulting image quality will be. The
best size for your video is highly dependent on your data rate, frame
rate, codec, source material, and personal preferences. All of these factors
are deeply interrelated, so experimentation is the best way to find the
optimal setting for your project.
One of the most important decisions you must make when preparing movies
is choosing the data rate. More than any other factor, the data rate affects
the final image and sound quality of your movie. It also affects how the
final file will be, as well as what playback methods will be able to effectively
delivery the movie.
There are two confusingly similar units used for measuring data rates.
Most multimedia developers are familiar with KiloBytes per second (kps,
KBps, or KBytes/sec) whereas many people working in Internet video specify
files in kilobits per second (kps,kbps, or kbits/sec). A byte is eight
times as large as a bit, so it is important to understand in which unit
a data rate is specified.
NOTE: When specifying data rate units (either bits or bytes), a capital
"K" is used to denote 1024, which is normally used for multimedia
applications. A lower case "k" is used to represent exactly
1000, which is often used in the telecommunications industry. A capital
"B" = a "Byte", a lower case "b" stands
for a bit.
It is fairly common for developers new to network video to assume the
rating of a modem is specified in KBytes /sec, which is incorrect. A 28.8
modem transfers 28.8 kilobits/sec, not 28.8 KiloBytes/sec. A data rate
of 28.8 kilobits/sec equates to about 3.5 KiloBytes/sec -a major difference
from the asumed 28.8 KBps.
-- Data Rate Limiting Factors
Usually there are three factors that dictate the data rate you can use
on your movie. The media or connection speed, the amount of video you
need to fit onto your disc, and the speed of the minimum target machine.
-- CD-Roms
Generally for CD-Roms, a total darta rate of 170-200KBps is safe for 2X
speed. Safe 4X CD-Rom data rates are around 250-300KBps.
-- Web/Internet
There are a wide range of connections to the Web, and the
volume of web traffic at any given time substantially affects the possibile
throughput. Because of this, there is no way to guarantee the data rateyour
viewer will be able to see in realtime even if you know what connection
they are using. . However if you want your viewer to be able to watch
your video in realtime, the following numbers are reasonable starting
points:
28.8 Modems-2.5 KBytes/sec (20kbits/sec)
56.6 Modems-4KBytes/sec (32 kbits/sec)
Dual ISDN-12 Kbytes/sec (96 kbits/sec)
T1-20KBytes/sec (160 kbits/sec)
