Encoding to a Windows Media File


The uncompressed movie takes up 80 to 120 GB of storage space and streams at nearly 150 Mbps. However, after the movie has been compressed and encoded to a Windows Media file, size and bit rate will be substantially lower. The final Windows Media file will be several hundred megabytes and the bit rate that produces acceptable-quality broadband video can be as low as 300 Kbps.

To achieve this high level of compression, Windows Media 9 Series codecs and the encoder use a number of algorithms. A simple compression algorithm can achieve a 1:2 or 1:3 compression ratio. However, for streaming digital media over a network like the Internet, you need compression ratios in the neighborhood of 1:24.

In order for codecs to compress data that much and still produce acceptable audio and video, streaming media codecs must use more advanced compression techniques, such as psycho-acoustic and psycho-visual modeling. The codecs selectively eliminate and modify data so that the result appears and sounds acceptable, even though it is different from the original. For example, subtle variations in color can be reduced because that type of visual information is not that important to our perception. On the other hand, the codec must attempt to maintain the appearance of smooth motion because subtle details of motion are important to our perception.

Codec usage is somewhat subjective. One setting will not work for every type of audio and video. This is why Windows Media Encoder provides many different settings and predefined configuration profiles. You can use the pre-configured settings by selecting the destination for your digital media, the type of audio and video content, and the bit rate. Settings can be individually configured to optimize encoding to meet your particular needs.

The Contoso staff will use a pre-configured template and modify it to achieve the desired result. To encode the uncompressed AVI file, the operator opens Windows Media Encoder, and then follows these steps:

  1. On the Wizards tab of the New Session dialog, select Custom session. The Session Properties dialog box of the new session opens.

  2. On the Sources tab, specify to source from a file. Then enter the path and name of the uncompressed AVI file.

  3. On the Output tab, select the Archive to file check box, and clear the Push to server and Pull from encoder check boxes. Then specify the file to encode.

  4. On the Compression tab, specify the following settings:

    • For Destination, select Windows Media server.

    • For Video, select Multiple bit rates (CBR).

    • For Audio, select Multiple bit rates (CBR).

    • For Bit rates, select the 282 Kbps and 764 Kbps check boxes.

      For better quality, you can also select Two-pass encoding on this tab.

You could continue to the next tab from here and the Windows Media 9 Series audio and video codecs would be automatically configured with optimum settings. However, the Contoso staff will modify the following settings to achieve encoding results that are better optimized for their intended use:

  1. Click Edit, and the Custom Encoding Settings dialog box appears. With the tabs in this dialog box, you can make fine adjustments to codec settings. The Contoso operator will modify several settings to enable nonsquare pixels so the output frame sizes are proportional to the dimensions of the source.

  2. On the General tab, select the Allow nonsquare pixel output check box. On this tab, you can modify properties that affect the overall encoding process, such as selecting different audio and video codecs, and specifying the video format.

  3. On the 764 Kbps tab, enter a video size of 720 x 480. End users connecting to the Contoso Windows Media server with a bandwidth supporting 764 Kbps will receive full-frame video. On the target bandwidth tabs, you can modify settings for each stream in an MBR stream, such as the frame size, frame rate, and video smoothness.

  4. On the 282 Kbps tab, enter a video size of 360 x 240. End users connecting with a bandwidth supporting 282 Kbps will receive video at half the width and height.

  5. Close the Custom Encoding Settings dialog box.

  6. On the Video Size tab of Session Properties, select Same as input for Pixel aspect ratio.

  7. On the Processing tab, select Inverse telecine. This process removes the redundant video fields that were added when the movie was transferred to videotape. For more information about inverse telecine, see chapter 1.

  8. Click Apply, and then click Start Encoding.

The Contoso encoding operator will be able to view the encoding process in the Video and Monitor panels. The video display shows either the input video, output video, both, or a split screen.

When encoding is finished, the operator opens the file in Windows Media Player and checks the playback quality of the high-bit-rate stream. If you want to check the other MBR stream or streams, copy the file to a Windows Media server. Then play the file over a lower bandwidth connection or limit the bandwidth manually in the Player.

To limit Player bandwidth:

  1. Start Windows Media Player.

  2. On the Tools menu, click Options.

  3. On the Performance tab, select Choose connection speed, and then choose a speed that is between the stream you want to check and the stream above it. The server sends a stream that is no faster than the bandwidth selected.

The production workstation is now up and running, and the operator has created a high-bandwidth MBR file. After she is sure the Windows Media file plays as expected, she can delete the large AVI file and capture the next movie or trailer. She can also try other features of the encoder that enable her to improve quality and the end user experience, such as two-pass encoding, VBR encoding, and deinterlacing.

In the last part of this chapter, Contoso will create a border that adds functionality and branding to content in Windows Media Player.




Microsoft Windows Media Resource Kit
Microsoft Windows Media Resource Kit (Pro-Resource Kit)
ISBN: 0735618070
EAN: 2147483647
Year: 2005
Pages: 258

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