Using VBR encoding

Windows Media Encoder supports three VBR encoding modes:

• Quality-based VBR. With quality-based VBR encoding, you specify a desired quality level (from 0 to 100). Then, during encoding, the bit rate fluctuates according to the complexity of the stream—a higher bit rate is used for intense detail or high motion, and a lower bit rate is used for simpler content. The advantage of quality-based VBR encoding is that quality remains consistent across all streams for which you specify the same quality setting. The disadvantage is that you cannot predict the file size or bandwidth requirements of the encoded content before encoding. Quality-based VBR encoding uses one-pass encoding. This mode is good for archiving content.

  If you are encoding audio content with this encoding mode, you have the option of using the Windows Media Audio 9 Lossless codec. Lossless encoding produces superior quality results, while also providing some compression of the data.

• Bit rate-based VBR. With bit rate-based VBR encoding, you specify the desired average bit rate. At any point, the bit rate may exceed the average bit rate but the overall bit rate does not exceed the average bit rate. Bit rate-based VBR encoding uses two-pass encoding. In the first pass, the data complexities are analyzed. Then, in the second pass, the quality level is set to achieve the average bit rate. The advantage of bit rate-based VBR encoding is that the compressed stream will achieve the highest possible quality level while staying within a predictable average bandwidth.
• Peak bit rate-based VBR. Peak bit rate-based VBR encoding is similar to the bit rate-based mode, except that you also specify the peak bit rate. The encoder determines the image quality that can be achieved without exceeding the peak bit rate. The bit rate does fluctuate during encoding, but does not exceed the specified peak bit rate. Use this option when you plan to distribute the content for playback on a device that has a constrained reading speed, such as a CD or DVD player. Peak bit rate-based VBR encoding uses two-pass encoding.

Notes

• Only certain codecs support VBR encoding.
• The quality-based and bit rate-based VBR encoding modes are not recommended for use in a streaming scenario as a result of the high bit rate peaks in the content. In a streaming scenario, when all players reach the point in the stream with a high bit rate at approximately the same time, there is a large peak in demand. This peak may exceed the network capacity, resulting in a negative playback experience.

Related topics

• Customizing a session
• About CBR or VBR encoding
• Using CBR encoding
• Feature requirements
• About one- or two-pass encoding
• To set up a quality-based VBR encoding session
• To encode lossless audio
• To set up a bit rate-based VBR encoding session
• To set up a peak bit rate-based VBR encoding session