Occasionally compression requirements dictate that you use a Constant Bit Rate (CBR) instead of a Variable Bit Rate (VBR). This is especially helpful for video streaming. In our encoding platform, VBR is the default setting for Encoding.com since it generally provides much higher quality. For scenes where there is a high amount of action or detail, VBR will often spike up to 300% of the target bitrate. The reverse is also true, VBR will dramatically pull back on scenes with low detail.
Why would you use CBR?
CBR is far more constrained, with the actual bitrate only floating about 20% above and below the target. Some video playback devices have cheaper “chips”, hardware decoders with limited buffer that are unable to handle VBR. With MPEG-4 being built into most modern chipsets, this issue is largely going away. CBR is also often used in satellite television broadcasts, where many channels will be multiplexed into one transport stream with limited bandwidth.
Sample API tags for CBR:
If you wish to check your encodes, Winhoros Bitrate Viewer is a great way to scan your files and quickly get detailed bitrate information.
If you are having problems getting the bitrate you need, try using a lower value in the bitrate tag. If that doesn't work, please submit a support ticket with the Media ID # of the job.