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Encoding content for Advanced Fast Start

Windows Media Encoder organizes audio and video data into data packets that can be easily and efficiently transported over a network. When the packets arrive at the client, Windows Media Player 10 re-assembles the data in the correct order and plays the audio and video with the correct synchronization. Because the video buffer is typically larger than the audio buffer, it is common for the encoder to place the audio data in a packet that arrives after the corresponding video. When this occurs, the Player must wait for the audio to arrive before it begins rendering a stream because video cannot play without the accompanying audio stream.

Audio that arrives late is typically not a problem if startup latency is not an issue in the streaming scenario. However, when Advanced Fast Start is used to minimize latency, it is important that the audio arrive slightly before the video so the content can begin playing as soon as possible. To make sure the audio arrives before the video, you can create an encoder profile in which the audio and video buffers are the same size. The fixed audio buffer size is 1450 milliseconds (ms). Therefore, if the profile sets audio and video buffers to 3000 ms, the audio buffer is 3000 ms plus the fixed buffer size, or 4450 ms, which effectively places the audio data before the video data.

To create a profile that includes an audio buffer setting, first create a custom profile with Windows Media Profile Editor, and then add the setting by opening and editing the custom profile file with a text editor, such as Notepad.

To add an audio buffer setting to an encoding profile

  1. On the Start menu, point to All Programs, point to Windows Media, point to Utilities, and then click Windows Media Profile Editor.
  2. On the General tab, enter the following information:
  3. On the Bit Rate tab, enter the following information:
  4. Click Save and Close.
  5. In the Save Profile As dialog box, locate the Profiles folder (by default, %systemdrive%\Program Files\Windows Media components\Encoder\Profiles), and enter a file name for the profile.
  6. Close Windows Media Profile Editor, open a text editor such as Notepad, and then open the custom profile file.
  7. In the profile text, specify the bufferwindow value as 4450:
  8. Save the file.

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