Capturing and Encoding Content

The two main programs Contoso Movies Online will use to create content are a simple AVI capture utility (such as Windows Media 9 Capture or Amcap) and Windows Media Encoder. First, they will capture the content from a videotape and save it as an AVI file on a workstation. Then they will encode the final Windows Media file from the AVI file. After they have successfully encoded the final file, they can delete the AVI file and capture another tape.

Configuring Encoder Options

The alternative to the two-step method is to capture and encode directly in one step with Windows Media Encoder. This method is certainly acceptable in many scenarios. It does not make sense to double the time it takes to capture and encode a movie for no good reason.

However, Contoso Movies Online wants to encode with the best possible quality, and that means offering content encoded for broadband connections. To do that they need to capture at full frame size (640 x 480) and full frame rate (29.97 fps). They also need to encode at a bit rate that gives acceptable image and sound quality. Contoso will target 700 Kbps. They also want to encode with multiple bit rates, so end users can view movies over slower broadband connections.

To capture and encode files the way Contoso wants them in one step would require a very fast computer system. Capturing and encoding in one step requires a fast CPU because of the high volume of data that must be compressed in real time. At the time of this writing, a computer with dual 2.5 GHz processors can capture and encode acceptable 700 Kbps files. However, if you want higher-bit-rate content or to encode files with MBR streams, you need a much faster computer.

Contoso will use the two-step method. However, when you decide what methods you are going to use, you should take a look at the features provided by the encoder and the utilities for optimizing quality, which include two-pass encoding, VBR, device control, and Windows Media Stream Editor.

Two-pass Encoding

The methods most often used to encode content employ one-pass encoding, in which compression is applied, the data is encoded, and a file or live stream is created in one step. As soon as you finish capturing a video, for example, you can view the finished file. With two-pass encoding, the content is analyzed during the first pass, and then encoded in the second pass based on the data gathered in the first pass.

Two-pass encoding can result in higher-quality content because more information about scene composition is available for optimizing bit rate, frame rate, buffer size, and image quality. The main drawback is that two-pass encoding can take twice as long. Also, you can only use the two-pass method for file-to-file encoding. It does not work for encoding a live stream, for example. You can, however, use two-pass encoding with device control to capture videotape to a file.

Variable Bit Rate Encoding

In most cases, you configure the encoder to create content that streams at a constant bit rate. For example, when you encode a file for 100 Kbps, no more than 100 Kbps of bandwidth is used when the file is streamed over a network. To achieve a constant bit rate, the encoder varies the quality of the content.

However, there may be situations where you want the quality to remain constant and the bit rate to vary. For example, if you plan to distribute a movie on a CD or offer it as a download only, you do not have to be as concerned with how much bandwidth is required to play back the content. In those cases, you can use VBR encoding. You can also combine VBR with two-pass encoding and get peak bit rate-based VBR, in which the bit rate varies, but does not rise above a bit rate limit that you specify.

Device Control

You can configure the encoder to automatically control playback of a device, such as a camcorder or VTR. For example, you can create an edit decision list of selected shots from a tape, and the encoder will automatically control the camcorder and encode the video. You can also use device control with two-pass encoding. For example, you can select a video segment from a tape, and the encoder will automatically capture the video and encode it using two-pass encoding. Device control only works with devices that connect through an IEEE 1394 port or that employ the Sony RS422 protocol, such as a Digital Betacam.

Windows Media Stream Editor

Rather than encode an MBR file directly, you can encode multiple single-bit-rate files and then combine them into one MBR file with Windows Media Stream Editor. This can be useful if you must capture and encode in one step on a computer that does not have a CPU that is fast enough to encode MBR at the same time. Windows Media Stream Editor, a utility that is installed with Windows Media Encoder 9 Series, also enables you to split one file into multiple files, and to support multiple languages by combining audio files.