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Set Video options

The Video settings in the Encode panel of Microsoft Expression Encoder specify overall video quality and playback parameters. The choices that you make here determine the complexity of the encoding process, and also how smooth the playback will be. Some of the settings described in the following sections may be available only for certain output formats.

For more information about output formats, see Set Output formats.

To set video options

  1. Click the Encode tab.

  2. Set the Video options according to the following guidelines:

    • Set Mode to specify whether Expression Encoder uses Constant Bit Rate (CBR) or Variable Bit Rate (VBR) encoding. For CBR encoding, you can choose CBR 1-pass or CBR 2-pass encoding. This specifies that the codec will make either one or two passes through the data when encoding it. In one-pass encoding, Expression Encoder uses only one pass through the content to analyze and compress it. In two-pass encoding, the codec first analyzes the content, and then, in the second pass, encodes it. This can create a higher-quality file.

      NoteNote

      2-pass encoding is not available in a Live Broadcasting Project.

      For more information about CBR and VBR encoding, see Understanding different types of bit-rate encoding.

      For VBR encoding, you can choose between 1- or 2-pass encoding only if you choose MP4 as your output format.

      • Choose VBR peak constrained to obtain a generally higher peak bit rate than the average bit rate, but to limit the variation. This is an ideal codec to use for most progressive download and local playback scenarios.

      • Choose VBR peak unconstrained to specify that there be no limit on bit-rate variance during the encoding process. This means that there can be great variations in the bit rate on playback. You should use this mode only if you are certain that the playback medium will be able to handle possible sudden increases in the bit rate.

      • Choose VBR Quality to achieve the highest bandwidth based on the Quality value that you choose. Note that the VBR Quality setting may cause sudden increases in bit rates in the encoding if the scene being encoded is a complex one.

      NoteNote

      Two-pass encoding does not take twice as long to encode as one-pass encoding. The first pass is faster than the second, so total encoding time increases only by roughly 20 percent.

    • Set Buffer Window to specify, in seconds, the amount of content that you want to preload before playing back. The 5-second default is, generally, an ideal setting. Larger buffers can increase the startup or seek time of your video.

    • Set Frame Rate to specify the number of frames per second (fps) in the encoded file.

    • Set Key Frame Interval to specify the number of seconds, or frames, between key frames.

    • Use the Stream tabs to add multiple streams to your content. You can use multiple streams to encode content of varying bandwidths to compensate for the different playback scenarios of your audience. If you choose MP4 or Windows Media as an output format, by default, all the streams that you create are combined and encoded in a single file. However, you can choose to encode each stream as a separate file. To display the settings for a particular stream, click a tab. If you choose IIS Smooth Streaming as an output format, by default, each stream is created as a separate file. If you choose MP4 as an output format, you must create a separate file for each stream. Also, by default, the IIS Smooth Streaming file format adds several streams to your job. For the other output formats, you will need to manually add any additional streams. To add a new stream, click a blank stream tab.

      NoteNote

      MP4 is not available as an output format in a Live Broadcasting Project Therefore, H.264 options are also unavailable.

      Depending on the Output Format that you choose, you will be able to control overall encoding quality by adjusting the Bitrate, Average Bitrate, Peak Bitrate, or Quality values. Drag the value to change it. The bitrate values are expressed in kilobits per second (Kbps). Higher Bitrate values create larger files and higher quality, but they also require more bandwidth for streaming. Set the bitrate options according to the following descriptions:

      NoteNote

      Some of the below options are not available in a Live Broadcasting Project.

      • Set the Average Bitrate value to the bit rate that you want to make sure that the entire file averages. You generally set this to help control file size.

      • Set the Peak Bitrate value to the maximum bit rate that you want for your bit stream.

      • Set the Quality value to adjust how much detail the final video will retain. The higher you set the value, the more detail is retained, and, therefore, the higher the quality (and the larger the file size) will be.

    • Drag the Width and Height values to change them. Increasing these values may cause distortion. To avoid distortion, either decrease the image size or keep the image at its original size.

    • Select Allow automatic resizing to instruct the decoder to allow a group of pictures (GOP) to be resized during playback. One way that smooth streaming playback optimizes available network bandwidth is by resizing frames during playback. This resizing enables the video to continue to play back at a high bit rate, despite the reduction in bandwidth. Note that the visible size of the frame does not appear to change, so that the resizing is not noticeable. However, the affected GOP may display a reduction in quality. This option is active only if you have selected IIS Smooth Streaming as the output format and VBR Constrained as the video mode.

    • Select Create separate file per stream to save an individual file for each bit rate that you specify. If you do not select this option, Expression Encoder combines all the streams into the final encoded file. This item is selected by default if you choose IIS Smooth Streaming as an output format. If you choose MP4 as an output format, this value is selected and cannot be changed.

    • Select a Video Aspect Ratio from the menu either to match your source or to match one of the listed aspect ratios. If you want to create a custom aspect ratio, click the lock icon and drag either Display value.

    • Select Force Square Pixels to make sure that your output contains square pixels.

    • Choose a Resize Mode to specify how you would like to display your video when the source video size does not match the output video size. You have the choice of instructing the encoder either to use Letterbox or to Stretch your video to match the output size.

See also

Send feedback about this topic to Microsoft. © 2011 Microsoft Corporation. All rights reserved.

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