2009

Another possible approach is to upconvert previously recorded compressed media by
connecting the SDI or HD-SDI output from a video deck or camcorder to the input of a
video capture card, thus using the deck’s circuitry to upconvert the compressed signal
to an uncompressed media file during capture. However, this doesn’t actually provide
access to any additional pixels or samples of information. Depending on the hardware
you’re using, there will be some filtering and interpolation of the video signal’s
components, but this process simply alters the data that was originally recorded. It’s
debatable how much of a visible increase in apparent image quality is provided, and
whether it’s worth the additional hassle.
The bottom line is that simply transcoding media from one codec to another in software
does nothing to improve image quality. Doing a hardware upconversion might or might
not have a noticeable effect on certain kinds of compression artifacts, but in most instances
it’s probably easiest to keep your media in the format in which it was originally shot
during the offline edit, preserving the data exactly as it was captured.
Keep in mind that once data has been discarded by compression in the camera at the
moment it’s shot, it is not retrievable, no matter what format you upconvert it to.
Note: Upconversion is not the same as format conversion, in which you change a clip’s
frame size, frame rate, and field handling in addition to the codec it uses. When doing
format conversion, using specialized software (such as Compressor), third-party plug-ins,
or dedicated hardware can result in a dramatic improvement in the final result. For more
information about format conversion, see “Format Conversion When Finishing
Mixed-Format Sequences.”
Are there other advantages to upconverting compressed media?
There are other legitimate reasons to transcode media from one codec to another. For
example, you may find that working with some highly compressed formats natively is
more processor-intensive than working with versions of the same media transcoded to
one of the Apple ProRes codecs.
Another good reason to transcode is if the native resolution of the media is slightly
different from the frame size at which you want to finish the program, and you don’t
want to deal with resizing issues. For example, many compressed high definition
acquisition formats are anamorphic; DVCPRO HD may be recorded at 960 x 720, and HDV
may be recorded at 1440 x 1080. If you prefer working at the nearest full-raster frame size
in preparation for finishing, you may choose to upconvert your media to 1280 x 720 or
1920 x 1080.
Of course, that’s not the whole story.
68 Chapter 5 Finishing