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Mastering
and archiving
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In an
analogue videotape editing process each video or audio clip is selected
and copied from a player VTR to a recorder VTR.
The tape in the recorder becomes the master tape for the production, from
which broadcast release masters and VHS copies may later be taken.
The master tape is an important archival resource - we produced at least
one master tape of each production - even those edited and archived
digitally. |
Mastering on Betacam SP
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In
the non-linear digital editing process, the raw material is copied
(digitised) to the hard drive storage medium, and the editing process is
simply a task of building a timeline script to get the editing computer to
play the required parts of the required clips in the required order -
without apparent interruption or delay. Such playback does not require a
master tape with its own edited copy of the original clips. The digital
master is simply a virtual playback script.
The digital and analogue output from a non-linear editing computer is
usually of a much higher resolution, or a different data format, than that
required for broadcast or distribution. When the editing process is
completed, the production must be digitally encoded into the necessary
formats for distribution on tape, network, CD, DVD or internet. |
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This
work - first undertaken when the production has been approved - comprises
the following tasks -
- A 33 megabit or 50 megabit "fused
sequence" digital master file is created
(this file can only be played back on the editing computer)
- The digital master file is copied to the
required professional analogue or digital videotape formats which will
be used for broadcast release, videotape duplication and archiving.
- VHS copies are pulled from either the
digital master file or videotape
- The necessary files for DVD authoring
are encoded from the digital master file
- Files required for CD or web release are
encoded from the digital master file
- Where relevant, web-compatible low
bandwidth files are encoded for client screening via the Channel 6
Television web server.
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Both
the digital master file and subsequent encoded files and videotape copies
are subjected to a critical quality control to ensure that release copies
derived from these are of the highest possible quality.
These files are also backed up and archived for future applications such
as duplication, production updates and language versioning; all of which
could be required many months or years after the original production is
completed.
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Mastering to DVD
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Similarly,
all production data - digital graphics, music, narration, audio
recordings, the project edit lists and all relevant administrative data
relating to the production is copied from the company's active servers to
both back-up servers and retrievable media.
Safety copies of Video CD or DVD releases are also made and archived. |
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| Archive
considerations |
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The
original raw video, audio or film recordings are held as a physical
archive. Although archiving on hard drive may be economically viable for
all production footage in the future, current storage technology remains
too expensive and requires video compression that may - in the light of
future digital technology - prove inferior when compared to re-digitising
from the original recording. Therefore any subsequent use of the footage
will require re-digitisation.
The development of digital video has progressed rapidly in the last decade
- giving rise to a multitude of videotape and drive based recording
formats, each with its own compression technology. Most of this technology
was developed first for standard definition television.
Now, with the
advent of wide screen and HDTV, industry professionals are continually
faced with the task of reformatting standard definition material, the use
of which will be common for many decades to come.
The major issue with digital video recording is one of compression – for
the digital cameras, video recorders and processing systems to be able to
handle, store and subsequently retrieve and deliver – large amounts of
data in real time, most digital video systems involve some for of
compression by which part of the original image data is “thrown away”
– to reduce the amount of data remaining.
Digital
video technology is certainly improving, but the fact remains that the
image from any compressed digital image is constructed from only a part of
the image information that originally was available to the camera lens –
somewhere along the way, this data has been disposed of to save space and
bandwidth.
This is rarely an issue when evaluating the image subjectively at the
first generation, because the compression algorithm used to compress the
data will usually reproduce the image without subjective loss or
artefacts.
When editing such material, the result will usually be of equal quality to
the original compressed” image – because it is an exact digital copy
– providing of course that the editing and copying is undertaking using
the same digital format and compression standards as the original. If this
is the case, the end result will only have seen one process, in which data
has been discarded to achieve compression.
But with today’s plethora of differing acquisition, editing, storage,
mastering and distribution standards and formats, this is rarely the case.
The same is true of most
transitions, effects and rendering in the digital editing process. When
two images are combined in a dissolve or transition effect, some data must
be discarded. Simply mixing for example – two 24 but data streams first
results in a 48 bit combination, which must be reduced to 24 bits by
“dithering” the least significant bits of data – the precise
algorithm for how such dithering is accomplished is different in every
proprietary digital processing system.
Many broadcasters have encountered regrettable degradation of the digital
image as it passes through many generations of digital compression and
videotape recording –
each using different digital standards and compression algorithms.
Whilst broadcasters are under considerable economic
and technological pressure to embrace each standard as it becomes
available, an independent production company such as Channel 6 Television
is able to take a longer view, as our only consideration is which formats
to use for acquisition and release.
For this reason Channel 6 Television has chosen to retain Betacam SP or
equivalent uncompressed digital acquisition technology until the company
makes the transition to a high definition widescreen format - to ensure
that all media recorded in standard definition remains uncompressed in
archive until the needs of the future are determined.
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channel 6 television denmark
Foerlevvej 6, Mesing,
8660 Skanderborg
Telephone 86 57 22 66
Telefax 86 57 22 16 |
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