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

CHAPTER 6: Setting Encoding ParametersThe Leaky Bucket AlgorithmThe video buffer is the normative MPEG-4 video buffering verifier (VBV). TheVBV is the instantaneous bit-rate smoother, or transmission buffer, thatensures that the instantaneous bit rate never exceeds the target bit rate behindthe video buffer. You can also use it as a reception buffer.Single-pass/double-pass encodingAlthough it is specified at the Job level of the encoder, 2-pass encoding isspecific to the video codecs.For offline encoding only, you can select either the single-pass or double-passencoding, by selecting the Enable double-pass radio button. Double-passencoding is for offline encoding with Helix Mobile Producer On-Demand. Ituses information from the first pass to reallocate the bits during the secondpass. This enables you to encode video input at a very high level of quality.Keep in mind though, that double-pass encoding takes twice as long as singlepassencoding.Two-Pass EncodingWith two-pass encoding, which is used only when encoding from a digitizedsource file, Helix Mobile Producer On-Demand runs through the entiresource video once to gather information about how best to encode thestreaming clip. It then makes a second pass to encode the streams. Two-passencoding can substantially increase clip quality, but it requires more encoding33