Mpeg-2 bit rates and formats – Apple Compressor (4.0) User Manual
Page 97
Chapter 5
Custom settings and output formats
97
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YUV 4:2:2 Color encoding (Not for DVD use): Select this checkbox to enable 4:2:2 color encoding.
This option is supported in the creation of MPEG-2 elementary, program, and transport
streams, but it’s available only when the Stream Usage pop-up menu is set to Generic.
•
Multiplexed MPEG-1/Layer 2 Audio: Select this checkbox to create a multiplexed stream (rather
than an elementary stream). You can make the output file either a transport stream or a program
stream. For information about the different stream types, see
on page 84.
The audio in this stream is MPEG-1 Layer 2, with a sample rate of 44.1 kHz or 48 kHz
(depending on the source) and a bit rate of 384 kbps. To create an audio-only (MPEG-1/Layer 2
Audio) elementary stream, see
on page 110.
Important:
Generic is the only Stream Usage setting that supports transport and program
streams. Selecting the Multiplexed MPEG-1/Layer 2 Audio checkbox changes your Stream
Usage setting to Generic if it’s currently anything else.
MPEG-2 bit rates and formats
The following sections contain useful information for creating MPEG-2 output media files.
Bit rates
When determining average and maximum bit rates for standard DVD playback, remember to
consider the bit rate of your audio track as well as the MPEG-2 bit rate.
You must keep the total of both average and maximum audio and video bit rates under 10.08
Mbps, the maximum guaranteed transfer rate from standard DVD players. Because DVD-
compatible audio formats are constant bit rate (CBR), there is no maximum audio bit rate to
worry about.
For example, if you’re using AIFF audio at 1.5 Mbps, you should keep both the average and
maximum video bit rates under 8.5 Mbps. Typically, your average bit rate is lower than this (for
example, 3.5 Mbps for 2 hours of footage on your DVD). However, your maximum bit rate must
also stay below this number. A maximum bit rate of 8.0 Mbps is recommended to provide an
extra margin for error (for example, to accommodate subtitle streams). If you’re using one of
the DVD-compatible compressed audio formats such as Dolby Digital or MPEG-1/Layer-2, your
audio bit rate may be as low as 0.2 to 0.4 Mbps, in which case you can set your maximum bit rate
about 1 Mbps higher.
Also, as a general rule, set your maximum bit rate at least 1 Mbps higher than your average bit
rate, to allow for bit rate variability in achieving the goal of constant quality.
The following table shows some average bit rates and corresponding footage times for a 4.7 GB DVD:
Average bit rate
Approximate duration for 4.7 GB DVD
3.5 Mbps
121 minutes
5.0 Mbps
94 minutes
6.0 Mbps
82 minutes
7.5 Mbps
68 minutes
8.0 Mbps
65 minutes
Note: When “One pass VBR” or “One Pass VBR Best” is chosen for very short clips (less than a
minute or two in length), the resulting MPEG-2 output file size may not accurately reflect the
average bit rate you specified. If the MPEG-2 output media file is larger than you want, you can
try transcoding it again at a lower average bit rate.