Apple Compressor 2 - Manual (Page 134)

134 Chapter 10 Creating MPEG-2 Output Files
Quality Tab
The Quality tab allows you to set the bit rate for your video so that it can be transcoded
to a suitable data size and quality.
In addition to the controls, the lower-right corner shows an estimate of how many
minutes of video would fit on a 4.7 GB DVD using the current settings. This time
assumes a single AIFF audio stream to be used with the MPEG-2 stream.
The Quality tab contains the following controls:
 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”: 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.
Mode pop-up menu
Time estimate for a 4.7 GB disc
with a stereo AIFF audio stream
Motion Estimation
pop-up menu