Video tape editing started with a primitive mechanical cut and join system on 2-inch tape. As tape formats changed more sophisticated electronic methods were devised but the proliferation of recording formats (including the introduction of disc) meant that nearly all formats have their individual designated editing systems or they need to be dubbed to the preferred editing format. In news programmes and in many other types of programming there is also the need to use library material, which may be originated on a superseded and/or obsolete format. The lack of the simple standardization of film (i.e. it is either 35 mm or 16 mm with the complication of changing aspect ratios) has meant that a number of different video editing systems have been devised mostly using the same basic editing methods but taking place in a variety of recording formats. To add to the variety of contemporary formats and the back catalogues of material are the conversion and compression problems posed by the transition from analogue to digital television. An edit suite or field edit system is therefore defined by its analogue or digital format and whether the shot selection is achieved in a linear or non-linear form.
Selective copying
Recorded video material from the camera almost always requires rearrangement and selection before it can be transmitted. Selective copying from this material onto a new recording is the basis of the video editing craft. Selecting the required shots, finding ways to unobtrusively cut them together to make up a coherent, logical, narrative progression takes time. Using a linear editing technique (i.e. tape to tape transfer), and repeatedly re-recording the analogue material exposes the signal to possible distortions and generation losses. Some digital VTR formats very much reduce these distortions. An alternative to this system is to store all the recorded shots on disc or integrated circuits to make up an edit list detailing shot order and source origin (e.g. cassette number, etc.) which can then be used to instruct VTR machines to automatically dub across the required material, or to instruct storage devices to play out shots in the prescribed edit list order.
On tape, an edit is performed by dubbing across the new shot from the originating tape onto the out point of the last shot on the master tape. Simple non-linear disc systems may need to shuffle their recorded data in order to achieve the required frame to frame whereas there is no rerecording required in random access editing, simply an instruction to read frames in a new order from the storage device.
Off-line editing allows editing decisions to be made using low-cost equipment to produce an edit decision list, or a rough cut which can then be conformed or referred to in a high quality on-line suite. A high quality/high cost edit suite is not required for such decision making although, very few off-line edit facilities allow settings for DVEs, colour correctors or keyers. Low cost off-line editing allows a range of story structure and edit alternatives to be tried out before tying up a high-cost on-line edit suite to produce the final master tape.
There are two types of linear editing:
Insert editing records new video and audio over existing recorded material (often black and colour burst) on a ‘striped’ tape. Striped tape is prepared (often referred to as blacking up a tape) before the editing session by recording a continuous control track and time code along its complete length. This is similar to the need to format a disk before its use in a computer. This prerecording also ensures that the tape tension is reasonably stable across the length of the tape. During the editing session, only new video and audio is inserted onto the striped tape leaving the existing control track and time code already recorded on the tape, undisturbed. This minimizes the chance of any discontinuity in the edited result. It ensures that it is possible to come ‘out’ of an edit cleanly, and return to the recorded material without any visual disturbance. This is the most common method of video tape editing and is the preferred alternative to assemble editing.
Assemble editing is a method of editing onto blank (unstriped) tape in a linear fashion. The control track, time code, video and audio are all recorded simultaneously and joined to the end of the previously recorded material. This can lead to discontinuities in the recorded time code and especially with the control track if the master tape is recorded on more than one VTR.
Limitation of analogue signal
The analogue signal can suffer degradation during processing through the signal chain, particularly in multi-generation editing where impairment to the signal is cumulative. This loss of quality over succeeding generations places a limit to the amount of process work that can be achieved in analogue linear editing (e.g. multi-pass build-ups of special effects). This limitation can be reduced by coding the video signal into a 4:2:2 digital form (see page 18).
Compression and editing
As we discussed in Motion compensation (page 16), passing on only the difference between one picture and the next means that at any instant in time, an image can only be reconstructed by reference to a previous ‘complete’ picture. Editing such compressed pictures can only occur on a complete frame.
Provided the digital signal is uncompressed, there is no limit to how many generations of the original are ‘rerecorded’ as each new digital generation of the original material is a clone rather than a copy. Imperfections introduced in the editing chain are not accentuated except where different compression systems are applied to the signal in its journey from acquisition to the viewer. Nearly all digital signals from the point of acquisition are compressed. Care must be taken when editing compressed video to make certain that the edit point of an incoming shot is a complete frame, and does not rely (during compression decoding), on information from a preceding frame.