30 Chapter 2: TARGA Specific Control Panels Within Adobe Premiere
format selected in the MPEG Output Type area. You can alter the bit rate per second here by
moving the slider via the mouse or typing a new value (up to 25) in the data field.
Note: For MPEG, the data rate is always referred to in MBit/sec, not MBytes/sec as used by older
compression formats. One MByte/sec is equal to 8 MBits/sec.
When exporting to the MPEG-2 format, the quality is not only set by the data rate, but also by
the GOP structure. In general the more “P” (picture or reference picture) and “B” (bi-
directional) frames selected for the GOP, the lower the required data rate will be for a given
quality.
The DVD standard permits a maximum data rate for video and audio of 9.8 MBits/sec. Note
that the data rate selected in this dialog refers to the video portion only. For one stereo track
of 48 kHz 16-bit PCM-codec audio, an additional rate of 1.536 MBits/sec is required and the
video may not be above 8 MBits/sec if your production target is DVD.
For MPEG-2 CD production, you can go to higher data rates if the CD-ROM drive you will
later use to play back your production will support this. However, high data rates will reduce
the length of the video that will fit on a CD. Fir example, at 8 MBits/sec the maximum length
is in the range of 10 minutes per CD.
GOP (Group Of Pictures) -- GOP within TARGA 3000 allows for two choices:
• DVD Standard -- Use if DVD is going to be the format used. A GOP size (length) of 15 and
an “M” (reference picture period) of 3 will be set. This will correspond exactly to the DVD
standard with the data rate set at 8 Mbits/sec.
• Custom -- Allows you to set your own GOP size. Note that some of the possible settings are
not legal.
—GOP M -- Represents the number of frames between “P” (reference picture) frames. You
can select 1, 2, or 3.
—GOP Size -- Represents the number of frames in a group of pictures, or the number of frames
between reference “I” frames. If you selected 1 for the number of frames in the GOP “M,”
your choices here are 1-15. If you selected 2 for the number of frames in the GOP M, your
choices here are 2, 4, 6, 8, 10, 12, or 14. If you selected 3 for the number of frames in the
GOP M, your choices here are 3, 6, 9, 12, or 15.
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