An increasingly frustrating problem for online editors is a fairly recent tedancy for Avid to experience a type of sync drift while digitising whole tapes at an offline stage.
This is not apparent at the offline stage, as the captured footage appears to have continuoius timecode, and in sync audio, however at online stage many clips can drift out of sync with the provided audio by as much as 18 frames (or potentially even more).
The problem is two-fold…
Firstly, it is a camera problem. A number of cameras (only Sony models it seems) appear to skip a frame or two when continuing timecode after powering off or entering standby mode. They do not miss any actual frames but the timecode of the first frame after this power cycle does not immedidately follow the timecode of the last frame recorded, instead it is one or two frames further on.
The second part of the problem is to do with the way Avid records timecode while capturing footage. Rather than recording exact timecode from the deck, it gets in sync with the deck when the capture starts and from then on simply counts frames. This isn’t normally an issue, as any discontinuities in timecode will be detected as a timecode break, and Avid will halt the capture. However, and this is a big however, Avid does not detect timecode breaks of less than six frames, so in when digitising tapes with the above problem, the timecode Avid records will get more out of sync every time it passes one of these break points.
While the audio and pictures are tied together as one stream in the offline, this is not a problem, however when it comes time to reconform the edit on another suite, problems arise. Because the batch capture process generally cues to within a few second of the required material, it syncs with the tape timecode at that point, and is again correctly in sync with the actual recorded timecode. However, this is not the timecode that has been recorded as part of the edited sequence, nor is it the timecode that the original audio was captured with.
To correct this problem, it is necessary to resync each shot in the new online sequence to the recorded sound, to counter the original inaccurate timecode recorded at offline time. There are a number of ways to achieve this in a non-linear environment, some are not even that difficult. However if the show is to be onlined on a linear suite, there is no way to correct the problem. It will introduce problems with audio sync, and often created flash-frames where shots have slipped enough to pass the end of a take.
There are a number of options available at the time of the offline, or even during the shoot, to help reduce this problem.
- Digitise tapes in smaller chunks
If offline tapes are digitised in segments of five or ten minutes, these small breaks to not continue to accumulate to create large sync discrepencies toward the end of tape, as they will if a tape is digitised as one single clip. - Shoot ‘Time of Day’
If shooting ‘Time of Day’ timecode it is impossible to create breaks of less than six frames between takes. However this can introduce other problems if tapes are used over multiple days or past midnight (00 comes before 23, decks have trouble figuring out how to cue). Another option might be ‘Free Run’ – However, in this case timecode breaks WILL be created, and care must be taken to allow for pre-roll at the beginning of all takes.