When to encode at a constant bit rate

Encode your content at a constant bit rate when you intend for it to be streamed on demand. The size of the buffer will determine the amount of initial delay when the video is started, but the constant bit rate will ensure that the content can be streamed smoothly, assuming that the bit rate is compatible with the client connection speed.

Windows Media 8 Encoding Utility enables you to choose between two modes when encoding at a constant bit rate. Choosing one-pass, mode 0, means that the content will pass through the encoder once. Compression is applied as the content is encountered, and the process is complete when all content has gone through the encoder.

Choosing two-pass, mode 1, means that the encoder analyzes the content during the first pass and then encodes in the second pass based on the data it gathered the first time. Two-pass encoding can result in better image quality because the encoder takes its time to find the optimal combination of bit rate, frame rate, buffer size, and image quality based on the scene composition. Two-pass encoding also takes longer because the encoder goes through all of the video twice.

Whether you are encoding your constant bit rate content in one or two passes, you must specify the desired bit rate, buffer size, and image quality settings using these parameters: -v_bitrate, -v_buffer, and –v_quality. For each of these parameters, keep these things in mind:

• The higher the bit rate, the better the image quality that you will be able to achieve.
  
  
• A larger buffer enables you to achieve better image quality, but the user will wait longer for the video to start.
  
  
• As the image quality increases, the frame rate decreases so you might have to experiment to achieve a balance between these two settings.

Related topics

• To encode in one pass using a constant bit rate
  
  
• To encode in two passes using a constant bit rate