Where did all those wires go?
From the dark days of analog, we are used to many
wires and cables coming out of the back of the capture card. With DV, there
is only one thin cable. This cable, the
Firewire, carries both video and audio, it carries device control
signals, and it does it in both directions. There's
no video in and video out, no audio in and out, no left or right, only
one wire between your camcorder and your capture card.
This is a Firewire cable,
using "Gameboy" style connectors
made by Molex. This picture shows
the standard 6-pin plug (front) and the 4-pin plug (rear) used by Sony
on their DV camcorders. Two of
the six pins on a Firewire plug carry power. The Sony camcorders don't
need this wire pair because
the camcorders run under
their own power.
DV & Firewire Editing Workflow
Step 1: Compression in camera.
As video is being shot, it is compressed and converted to digital
form in the camcorder. What used to be "video" now sits on a digital tape.
This digital tape can be played in a digital tape drive, such as the one
in your camcorder, in a DVCR, or in a standalone unit such as the DVDrive
sold by FAST.
Step 2: A transfer, please! DV
data, not video, is transferred electronically via the firewire to
the computer's hard disk. This not a capture process. it's a file copy
process. The copy process can be handled by a driver
camouflaged as a regular capture driver, or by a standalone utility. This
is specific to the individual implementation of the driver for the various
DV/Firewire boards, and it can also change as matter progress. The
hard drive has to be fast enough to cope with the 3.7 MByte/sec data rate
(plus some overhead). Theoretically, it is possible to stop the tape and
restart if and when the hard drives can't cope with the data rate, but
this is an involved process and may not be implemented in early versions
of DV drivers.
Step 3: You want it wrapped?
During the copy process, the DV data is "wrapped" into a file format commonly
understood by computers, in this case either AVI for Video for Windows
or Quicktime for the Mac. Both file formats allow for "installable
compressors," also known as codecs. AVI for instance can work with a multitude
of installable compressors, such as Indeo, Cinepack, VDO, etc. to name
just a few. The compressed DV data is treated like data produced by just
another installable compressor. As a matter of fact, there is a DV compressor/decompressor
(codec) installed on your system. But during the file copy process,
this codec is not needed. We'll cover that later in more detail.
Step 4: Look, Ma, no codec!
After the copy process has been finished, the DV data is sitting
on your hard drive, wrapped into a file format any standard editing application
can process. Note: The actual DV data has not changed. It hasn't been touched
by a codec, it hasn't been recompressed, changed or altered.
Step 5: DV Premieres. To edit
your clips, you use any standard editing application that can work with
industry standard file formats, such as the ubiquitous Adobe
Step 6: Ain't misbehavin'
During editing with a program like Premiere, your DV AVI or Quicktime movie
will behave just like any other video clips you used before.
Step 7: So where does
that codec come in? When, and only where Premiere adds filters
or transitions, Premiere needs the DV data in uncompressed form. For this,
Premiere will call the installed DV codec. Premiere will hand it
compressed frames retrieved from the AVI or QT file. Premiere receives
uncompressed RGB bitmaps back from the codec. Premiere then blends, filters,
combines, warps or alters these frames according to the specified transition.
When done, Premiere hands the finished RGB bitmap to the installed DV codec.
The codec compresses the bitmap to DV AVI or QT and hands it back to Premiere.
Premiere then stores it in the target file. The installed DV codec
can be implemented in hardware or in software. Read more about this interesting
Step 8: Don't touch that.
Clips without filters or transitions are not being touched by the codec
and simply copied to the target file. If you would have a project
which consists only of hard cuts, the codec wouldn't be called for editing
Step 9: Here we go again.
After all edits have been finished, the resulting file must be copied from
the computer to the DV device via Firewire. During this copying process,
the AVI or QT wrapper is removed, data specific to the receiving device
is adjusted or restored. This is usually done "on the fly" as data is sent
to the DV device. Some boards may need additional post processing.
The copy process usually is handled by a standalone utility, or by a Premiere
"Print to DV" plugin.
Step 10: (This is a
10-step program!) You are done! On your hard drive sits DV video,
most of it as pristine as you've shot it. No generation loss. You've
reached the holy grail of video editing. Right on your computer.