Optimizing the System

As mentioned previously, Contoso Movies Online will encode in two steps. In the first step, audio and video are captured to an uncompressed AVI file. When capturing content, data must flow from the capture card, through the computer, and to the hard disk unimpeded in real time. If something slows or stops the constant flow, the whole process can fall apart. Without a system for controlling the flow on a slow computer, data would continue to pile up until memory ran out. To prevent a computer from crashing if it gets behind, a capture program deletes data and drops frames that the computer does not have time to process. You may not see an occasional dropped frame, but you would notice hundreds or thousands of them.

With a high-quality capture card, a fast computer, lots of memory, a fast bus speed, and a hard disk or disk array with a fast read/write speed, Contoso’s workstations are capable of capturing high-quality video. However, they can take additional steps to help ensure the best capture quality.

You can minimize the amount of processing a computer is required to do by turning off any program or process that is not essential for the capture, such as anti-virus programs, screen savers, e-mail programs, and Web servers. Then create as little work as possible for the processor by capturing audio and video without compression. Not only does compression lower the quality of the content, it requires a great deal of processing speed and memory. A high-quality capture card can also help conserve CPU resources by performing pre-processing tasks such as deinterlacing and cropping. Also, formatting video data as an AVI file requires less processing than other formats, such as Windows Media Format.

As you capture, keep an eye on the capture program. A counter on the program interface shows the number of frames dropped. If a frame is dropped occasionally, you may be able to live with the results. However, if frames are dropped regularly, you should stop the capture and check CPU and memory usage. Many capture programs are designed to stop or slow the preview function if the processor cannot keep up with a capture, so do not be concerned if preview does not appear when you start capturing, or if the preview image is jerky. Use the number of dropped frames to determine the success of a capture.

When the capture is finished, you can start the second step of the process: using Windows Media Encoder to create a new Windows Media file from the AVI file. During this step, the encoder performs a number of processes that compress the original data to a smaller size and lower bit rate, and encodes the data to a Windows Media file. During this step, you should again turn off any unnecessary programs and services. However, because the process is not occurring in real time, the quality of the resulting file will not be affected and frames will not be dropped if the computer is not optimized for encoding. The processor works at its own speed when encoding from a file. Rather than dropping frames, the process simply takes longer.

As mentioned previously, digital videotapes are captured directly through the SDI port. However, when capturing an analog tape with the Digital Betacam, the waveform monitor/vectorscope will be used to properly adjust the video and color parameters. The videotape to be captured is inserted in the machine, and adjustments are made on the Digital Betacam while test signals recorded at the beginning of the tape are played back. After adjusting the machine with the test signals, the movie will play back with the proper video intensity and color. For more information about setting up the Digital Betacam for playing back analog tapes, see chapter 15.