Using CBR or VBR encoding

You can encode audio and video content at either a constant bit rate (CBR) or a variable bit rate (VBR). Use CBR encoding when you plan to stream the content. Use VBR encoding when you plan to distribute the content for downloading and playing either locally or on a device that has a constrained reading speed, such as a CD or DVD player.

• CBR encoding. With this option, bit rate fluctuations during encoding are constrained by the buffer size, and the image quality fluctuates to ensure that the buffer does not overflow or underflow. You can use either one- or two-pass encoding for CBR encoding.
• Quality-based VBR encoding. With this option, the content is encoded at a specified quality (from 0 to 100). During encoding, the bit rate varies to ensure the specified quality is met. Use this option when you do not care about the bit rate but want to ensure the quality of the output. This option uses one-pass encoding.
• Bit rate-based VBR encoding. With this option, the content is encoded at an average bit rate. At any point, the bit rate may exceed the specified average bit rate but the overall bit rate will match the average bit rate. No frames are dropped in this mode. This option uses two-pass encoding.
• Peak bit rate-based VBR encoding. This option is similar to the bit rate-based VBR option, except that the bit rate fluctuations do not exceed the peak bit rate. Use this option when the content will be played back by a device that has a constrained reading speed, such as a CD or DVD player. This option uses two-pass encoding.

Note

• If you encode content by using a profile that does not specify either CBR or VBR encoding, or if you set up a custom encoding session and do not specify CBR or VBR encoding, one-pass CBR encoding is used by default.

Related topics

• Advanced encoding techniques
• Implementing a CBR or VBR encoding mode