helix mobile producer on-demand user's guide - RealPlayer

Helix Mobile Producer On-Demand User’s GuideConstant bit rate (CBR)Use this option if your content is going to be streamed over a limited-bit-ratechannel such as a network. If you select this parameter, the output stream isdelivered at the single, constant bit rate that you’ve specified.Note: Selecting this setting might lower the quality of thevideo output. For MPEG-4 encoding, some video frames mightbe omitted to ensure that the output video stream conforms tothe CBR that you selected. Higher bit rate values reduce codingartifacts, but they use more of the available bit rate.When you create a clip, you can choose constant bit rate (CBR) or variable bitrate (VBR) encoding. In Helix Mobile Producer On-Demand, each audiencetemplate is either CBR or VBR. CBR encoding is the more traditional methodof encoding streaming video. It maintains a consistent bit rate for the stream,such as a constant 34 Kbps when streaming to 56 Kbps modems. You shouldgenerally use CBR video when streaming at bandwidths below 350 Kbps, andanytime you want to use a SureStream clip to encode multiple bandwidthsinto the same clip or broadcast. At high bandwidths, however, you can useCBR or VBR video.Variable bit rate (VBR)Use this option to set the variable bit rate, or average bit rate, for encoding thevideo. This bit rate is expressed in kilobits per second (Kbps). By default, themaximum bit rate is twice the average bit rate.Variable bit rate encoding generally provides superior video quality toconstant bit rate encoding. It gives more bandwidth to scenes that are hard tocompress, making the most visible difference in videos that have fast moving,high-action scenes. VBR is not compatible with SureStream technology,however, so you can encode a VBR clip only for a single bandwidth. VBRencoding is suited for bandwidths of 350 Kbps or higher.Unlike a CBR clip, a VBR clip does not maintain a constant streaming rate.Instead, it has a target average bit rate (or quality) and a maximum bit rate.For example, Helix Mobile Producer On-Demand’s 450 Kbps VBR downloadaudience averages 450 Kilobits of data per second. However, the audience has amaximum of 900 Kbps, meaning that the stream can, if necessary, consumeup to 900 Kilobits of data a second. These data spikes typically occur duringhigh-action sequences, resulting in greater video clarity and higher frame ratesthan CBR encoding.30