The Internet is swiftly becoming the next great broadcast medium. RealSystem G2 lets you broadcast live or prerecorded presentations over the Internet or your intranet. This chapter explains how you use encoding tools and RealServer to set up broadcasts.
When a streaming presentation is delivered on demand, its starts from its beginning when the viewer clicks the presentation link in a Web page. Each viewer can receive the presentation at any time and use RealPlayer's controls to fast-forward or rewind through the presentation.
In a streaming broadcast, however, the user hosting the broadcast starts the presentation at a certain time. Viewers who click the presentation link join the broadcast in progress. Before the broadcast begins and after it completes, the presentation URL is not valid. During the broadcast the RealPlayer fast-forward and rewind controls do not function.
To make an analogy, on-demand content is like a movie on videotape. The viewer can see it at any time, skip forward, rewind, and pause. A streaming broadcast, though, is like a movie broadcast on a television channel. As with a TV broadcast, there are two types of streaming media broadcasts:
Live content is broadcast as it occurs. For example, you can broadcast the output of a video camera across the Internet or an intranet. RealSystem encodes the content as RealVideo in real-time without writing the content to a RealVideo clip first.
Prerecorded content consists of video or audio you record and write to a digitized clip. You can then edit the clip before converting it to a streaming format and broadcasting it across a network. To the viewer, the presentation looks just like a live broadcast.
To broadcast a presentation, you need the following tools:
This equipment captures the broadcast content. It is typically a microphone or video camera connected to a audio or video capture card. For text it could be a live text feed coming in over a network.
When you broadcast prerecorded content, you first write the source to a digitized file. You can then use editing software to optimize the file for broadcast. When broadcasting live content, though, content goes directly from the capture equipment to the encoder.
The encoding tool takes the broadcast source and encodes it in the appropriate streaming format. When the broadcast is live, the tool sends the encoded output directly to RealServer. A RealVideo encoder, for example, encodes a camera's video output as RealVideo in real-time. A live encoder typically runs on a separate machine that has a network connection to the RealServer machine.
RealNetworks encoding tools have live encoding capability for audio and RGB or YUV video. Their broadcast wizards guide you through the encoding process and let you connect to RealServer easily. RealSystem's open architecture also lets you build an encoding tool to send RealServer any type of data for broadcast. For example, you could build an application that adds RealText mark-up to a stock ticker feed and broadcasts the output in real-time.
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Additional Information |
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| Visit http://www.real.com to download RealNetworks tools or the RealSystem G2 Software Development Kit (SDK), which you use to build a broadcast application. You can also get RealText Authoring Guide, which explains RealText mark-up. |
RealServer streams the broadcast to your audience. You will need to work with the RealServer administrator to get the broadcast URL and the parameters for connecting an encoding tool to RealServer. Because each RealServer has a limit on the number of streams it can produce, verify that the RealServer you intend to use has broadcast capabilities appropriate for your anticipated audience size.
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Tip |
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| Real Broadcast Network (RBN) provides full services for encoding and broadcasting events to a few or a few thousand viewers. See http://www.real.com/rbn for details. |
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Additional Information |
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| RealServer Administration Guide, available at http:// www.real.com, explains how to configure RealServer for a broadcast. |
The following are tips for preparing a live or prerecorded broadcast. See the manual or online help for your encoding tool for instructions on how to encode and broadcast content.
SureStream codecs introduced in RealSystem G2 let you broadcast RealAudio or RealVideo at multiple bandwidths. Each viewer's RealPlayer G2 then selects an encoding appropriate for its connection. Older versions of RealPlayer cannot receive a SureStream broadcast, however. RealNetworks encoding tools let you specify SureStream when you begin the broadcast.
To broadcast with non-SureStream codecs, you need a separate encoder application running on a separate computer for each bandwidth connection you intend to support. This is required because non-SureStream codecs require more CPU for each encoding than do SureStream codecs. You then connect each encoder computer to RealServer and broadcast the different encodings under different URLs. Each viewer decides which URL to choose based on their network connection speed.
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Additional Information |
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| For more on codecs, see "Choosing RealAudio Codecs". |
Refer to your encoding tool's manual or online help for guidelines on machine requirements for broadcasting. The efficient SureStream technology can broadcast multiply encoded bandwidth streams in real-time using just a moderately powerful PC. In general, encoding a 176x128 pixel RealVideo window using a frame rate of 4 to 15 frames per second requires a machine with the power of a 200 MHz Pentium computer. For higher frame rates and larger screen sizes, use a machine approximating a Dual Pentium 2.
RealNetworks encoding tools let you write a live broadcast to a file. RealServer can also archive the broadcast to a file. The latter optional may be the better solution if your broadcast is long and your encoding machine has limited disk space. The RealServer administrator can set up RealServer to archive the live broadcast.
The RealServer administrator can give you the parameters you need to connect an encoding tool to RealServer. The administrator will also provide the broadcast URL or URLs.
When you broadcast live content, you don't get a second chance. So it's good practice to perform a trial run to ensure that the equipment works properly and the broadcast results are what you expect. Because you can't edit a live broadcast the way you can edit a prerecorded file, it's important to set your audio levels and plan your video shots carefully in advance.
During both the trial run and the live broadcast, view the broadcast ourput with RealPlayer. When RealPlayer connects, check that the buffering time for receiving a live RealVideo stream does not exceed 5-10 seconds. Throughout the presentation, keep an eye on the broadcast quality.
If you experience problems with the encoded output, use the encoding tool to lower the video frame size and frame rate (fps), or select lower-bandwidth codecs. If these adjustments do not help, you may need to run your encoder on a more powerful machine.
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Additional Information |
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| For pointers on producing audio, see "Recording Audio". For video, see "Recording Video". |
Using SMIL, you can easily embed your broadcast in a multiclip presentation. You might use a SMIL file, for example, to create a video region for your live broadcast and a RealPix region that features rotating ads. The SMIL file then uses the broadcast URL for the video region and a standard URL to the RealPix clip.
Keep in mind, however, that SMIL does not synchronize on-demand clips with the broadcast. When the SMIL presentation starts, the viewer begins to receive the on-demand clips in the order they are defined by the SMIL grouping and timing tags. The viewer joins into the broadcast in progress, however. So if you set up ad rotation through SMIL, viewers receive ads relative to the time they click the presentation link. Thus all viewers will not see the same ads at the same points during the broadcast.
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Additional Information |
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| See Chapter 7 for information on SMIL. Visit http:// www.real.com to get RealPix Authoring Guide, which explains RealPix presentations. |
If you are broadcasting content that has wide public appeal, advertise your event on Timecast (http://www.timecast.com), the online guide to RealAudio and RealVideo.
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Additional Information |
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| "Advertising on Timecast". |