Image Processing Reference
In-Depth Information
Note also that some codecs may be faster or slower than others. During tests, the
H.264 codecs I checked out were all prototypes, and they took a significantly longer time
to compress the test video than the MPEG-2 encoders did. The Windows Media encoder
took even longer. However, the longer processing times yielded smaller files, lower bit
rates, and better-quality output.
Processing Without Compromising Speed
The speed at which you are encoding your video depends on how you are delivering the
content. Mainly this will determine whether you buy expensive hardware solutions or
much cheaper software solutions that run on commodity hardware. For example, you
might be
Streaming or broadcasting a service and playing out the original content live.
Preparing a file to be downloaded completely before playback.
Making material for playback from some local storage such as a DVD.
Recording a live broadcast in a home recording machine.
At the broadcast end, the content is stored at a very high bit rate and this normally
has only the slightest compression applied. That compression is visually undetectable any-
way. Commonly the DV50 and DV25 formats are used. These store the video at bit rates of
50 and 25 Mbps respectively. DV25 is becoming popular as a consumer format as well.
The content is played out through a series of processing systems to compress and
multiplex together a variety of different programs that are being broadcast simultaneously.
This kind of system cannot drop frames. It must deliver the streams continuously, 24 hours
a day, 7 days a week, and it must not exceed the budgeted bit rates or the transmission
chain will break down. Chapter 14 examines statistical multiplexing, an important tech-
nique that drastically affects the coding quality. Simultaneously encoding several streams
of video is a very hardware-intensive process and software is not often applied to that
task. Faster computer architectures may change that assumption over the next few years.
Preparing content to be downloaded and played back locally is far less time-inten-
sive. The processing is not constrained to operate at the same speed at which the video is
watched. The process can go faster or slower. Here you have an opportunity to run the
software on faster and more expensive commodity hardware and get more work done. Or
you could save money and deploy just a single, slower machine and wait while it encodes.
Examples of this kind of processing are the movie trailers that are posted on the Internet.
Compression Master is a tool that has a lot more settings available for you to parameter-
ize the compression process. Some tools simplify this to the point of giving you almost no
control at all. Compression Master lets you fine-tune the coding and requires some expert-
ise when operated at this level. It presents the settings in the foreground of the user inter-
face in what I think is a more accessible way than having to bring up another window to
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