Apple Compressor 3 - Manual (Page 202)

The Quality tab contains the following controls:
Mode pop-up menu
Time estimate for a 4.7
GB disc with a stereo
AIFF audio stream
Motion Estimation
pop-up menu
• Mode pop-up menu: Allows you to choose one of the following MPEG-2 encoding
modes. High Definition (HD) quality modes will be “One pass VBR Best” or “Two pass
VBR Best.”
• One pass CBR: Using this mode, the output MPEG-2 video stream’s bit rate is held
approximately constant from one GOP to the next. This is the fastest Compressor
MPEG-2 encoding mode, and it provides good to very good quality, especially at bit
rates between 5 and 9 Mbps.
• One pass VBR: This VBR (variable bit rate) encoding mode aims to maintain constant
quality (at the expense of constant bit rate) for the transcoded video file. This means
that in scenes with much detail or fast motion, Compressor allows a higher bit rate
than it allows in less detailed or still parts of the stream. In spite of this bit-rate
variability, Compressor ensures your specified average bit rate is achieved accurately
and that the maximum bit rate is not exceeded. Unlike the two-pass modes, one-pass
VBR doesn’t have a “bird’s eye” view of the source media prior to encoding, so its bit
allocation is less optimized than two-pass VBR. Nonetheless, for most standard
definition (SD) media files at bit rates of 3.5 Mbps and above, this mode provides
good to excellent quality and transcodes quickly.
202 Chapter 18 Creating MPEG-2 Output Files