Rendering
The rendering process is a long one, during which all the instructions are carried out on a frame-by-frame basis, pulling sound and vision data off the hard disc, processing it as required, and then progressively reassem- bling it back onto the HDD, which ideally is a separate one from that fit- ted as a part of the computer’s basic system. The programme-time capacity of a disk depends on the capture resolution and data-compres- sion rate chosen by the user in software. During replay the edited material comes off the hard disk as an .avi or .wmv files for de-interleaving, reverse DCT processing and data expansion: these take place on the capture card (codec) where the data is finally D-A converted and produced as composite video or S-video and baseband audio, a process called printing to video.
DV Editing
The A-D and data-processing involved in off-line computer editing of ana- logue video necessarily introduces degradation of picture and sound. Where the footage is captured in a camcorder to DV tape the data- compression ratio is fixed by the system at 5:1, with an excellent, tailor- made data-reduction algorithm. So long as this data is fully preserved during the editing and storage phases, it becomes possible to carry out ‘transparent’ editing, entirely in the digital realm, and with no degrada- tion at all of picture and sound quality, no matter how many generations of dubbing takes place. This is achieved with a DV capture card having a Firewire/i-link/IEE 1394 input/output port. It contains no A-D/D-A con- verters or data-compression systems, acting merely as a buffer/interface between the serial input line and the computer’s data buses. Of course it carries out many other functions in the realm of software/instruction implementation. Once editing is complete, it is exported back to the DV tape in a digital format using a Firewire facility.