The Real-Time Encoder encodes live or stored audio and video into an ASF stream, an .asf file, or both. The Real-Time Encoder is an extremely useful NetShow content creation tool for two reasons: it is the only tool that can accept a live source, and it is the only tool that can compress the video source (live or stored) so that the resulting ASF stream or .asf file will fit in a target bandwidth. All other tools require you to edit the video before you convert it to an ASF stream or .asf file. You can even use the Real-Time Encoder to convert .avi or .wav files into .asf files without doing any preproduction work. Because Real-Time Encoder can use video as a source, the encoder lets you set the size of the display window and choose a codec to compress the output ASF. Even if you are using live video and CD-quality audio as input, the ASF Real-Time Encoder can create an ASF stream with a 28.8 kbps bit rate.
The Real-Time Encoder does not deliver Active Streaming format information to clients (except for testing). The Real-Time Encoder converts live media, .avi, or .wav files to an ASF stream or to an .asf file. The Real-Time Encoder delivers the ASF stream that it creates to NetShow Server, which can then multicast or unicast the ASF stream over the network. If the Real-Time Encoder creates an .asf file, that file is saved to the directory that is specified during the configuration process. To play back an .asf file created by the Real-Time Encoder, use NetShow Player to open the .asf file. For more information on delivering the .asf file to NetShow Server, please see the NetShow System Administration Guide.
The computer that houses the ASF Real-Time Encoder must contain a sound card to encode live audio and a video capture card to encode video; you don't need either of these cards to encode an .avi or .wav file to an .asf file. The ASF Real-Time Encoder uses the inputs on the audio and video cards to receive the live source. For example, to multicast a live speech, you would plug the output from a video camera into the video card's input jack and plug the output from the microphone into either the video card's audio input or the input on the sound card (whichever input the encoder is set to use). The encoder acknowledges these input sources, receives the input, and encodes the audio and video into an ASF stream that is then delivered to NetShow Server.
To ready the ASF Real-Time Encoder, you must configure it. To configure the encoder, you can either open an existing configuration (.asd) file or create a new configuration. A configuration file contains the settings that the encoder will use. Some examples of the settings that the .asd file contains are the audio and video card the encoder will use, the audio and video codecs the encoder will use, where the encoder will send the ASF stream, what size the video display window will be, the pixel format that the video display will use, and so on. After opening an exisiting configuration or creating a new configuration, you can start the encoder.
The ASF Real-Time Encoder is not solely responsible for multicasting ASF information. When you configure the encoder for encoding information, you specify an output. The ASF information that the Real-Time Encoder outputs can be delivered to a NetShow server, can be written out as an .asf file, or both.
One other by-product of the ASF Real-Time Encoder is the ASF stream descriptor (.asd) file. You create the .asd file when you save the encoder's configuration. NetShow Server needs to know the information in the .asd file so that it can prepare to stream the ASF information associated with that configuration.
When the system administrator is preparing a channel on NetShow Server, she will get stream format information for the channel from the .asd file. She will then point the streams associated with that channel to the port number or stream alias defined in the ASF Real-Time Encoder configuration. For more information on .asd files and how NetShow Server uses them, please see the ASF Real-Time Encoder Help file and the NetShow System Administration Guide.
As for the ASF Real-Time Encoder, once you open the Real-Time Encoder, you should configure the encoder, save the .asd file (if you haven't already done so), and then start the encoder. There are a couple of ways that you can configure the ASF Real-Time Encoder:
Template .asd files are supplied to help you get started. When using a template .asd file, the network bandwidth, media, and codec properties are set, but you must walk through the configuration process and set the audio and video sources and the IP port of the Channel Manager that will receive the live ASF stream. Template .asd files are there to help you understand the codec combinations that can be used for specific network bandwidths.
When you open a saved configuration (that is, an .asd file that you or someone else has opened or created, and saved as your own), all properties of the encoder and your configuration are saved.
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