Making Avid Tapes in NTSC from 24 fps shows for DigiConform

Update!

The information on this page has been updated in this pdf. Please refer to it, rather than to the content of this page.

Long Instructions

Video captures in DigiConform systems omit one out of the two video fields that each video frame consists of. The omitted field can be either the first or the second field of video, and this is not selectable. However, both ways are fine. The result are 30 video frames captured for each 24 film frames, or 5 video frames for 4 film frames. In DigiConform, the user has to identify one redundant video frame out of five to be dropped from display - so that DigiConform can  display 4 video frames for each 4 film frames, using a 1:1 relationship between film and video frames. Every fifth video frame is dropped from display throughout the entire reel.

This works for projects cut in 24 frames per second only. The Avid internally works with 24 frames per second, and upon output it re-inserts the 2:3 pulldown in a rigid pattern throughout the entire tape. Any irregularity in this pattern throws DigiConform off.

Output tapes from the Avid have to be made with at least one audio track set to play during output.

It is not at all necessary to record audio on the video tape, but it is necessary to have the Avid play some audio during output. It may suffice to just turn on an empty audio track in the Digital Cut tool. If audio is not supposed to be recorded on the video tape, the input levels on the video deck could be turned down to zero. Alternatively, a level tone, e.g. 1kHz, could be recorded from a newly created audio track onto the tape.

Due to a little-known flaw in the Avid, the 3:2 pulldown cadence shifts slightly if no audio track is turned on during Digital Cut. This flaw seems to be mentioned in the release notes for Film Composers. The problem is known to be in Avid software versions 7.x, but it is likely to occur in all versions of Film Composer, including ones using the Meridien hardware. Internally, the Avid uses the audio sample clock for timing purposes, such as the 3:2 pulldown.

Make sure that the cut sequence in the Avid starts on a time code ending on 00 or 05.

This ensures the footage window burn to be in sync with the film frames. It is best to make the output tape in one pass, in order to preserve the ABCD pulldown throughout the entire reel.

This is the desired result, each film frame has one footage count associated with it (Note that the B-frame occurs twice, but has the same footage count):

When outputting a video tape form a 24 fps cut, the Avid re-inserts a 2:3 pulldown to make up for the difference between the film’s 24 fps and 30fps on video. By default, the first frame of the cut sequence is made an A-frame. (However, this can be changed in the Pull-In column in the bin the cut sequence lives in.)

The gear used to generate the footage burn at the dubbing facility (for example an Evertz After Burner) usually determines the 2:3 pulldown for the footage window based on the tapes time code, rather than based on the actual film image’s AABBBCCDDD pulldown-sequence. By default, frames with time codes ending on 00 or 05 are treated as A-frames. (However, this can be set differently.)

A tape with the footage-burn’s pulldown sequence out of sync may look like this:

In the Avid, the easiest way to make good tapes for DigiConform is to simply assign a time code ending with 00 or 05 to the first frame of the cut sequence and leave the Pull-In column at the default, which is A.

If given a choice of frame rates in the Digital Cut Tool, select 23.976 fps (not 24 fps).

Whether or not that choice is there depends on the software version of your Avid.

NTSC video decks run at 29.97 frames per second, without exception. This is true in spite of most people talking about 30 fps. The difference between 29.97 fps and 30 fps is not noticeable when playing back a tape.

When you record an output of a 24 fps film project to NTSC video tape, a rigid 2:3 pulldown pattern is applied make up for the difference between 24 fps (film) and 30 fps (video). But since the video deck runs at only 29.97 fps, the Avid has to slow down to 23.976 fps.

This happens automatically on Avids with software versions 7.x and below. Versions 10 and up give you a choice between 24 fps and 23.976 fps. If you run the Avid at 24 fps and the video deck at 29.97 fps, frames will be dropped roughly every 50 feet of film, or about every 33 seconds. Those tapes will not be useable in Digiconform.

Deliver tapes with a burn-in window of the sequence time code.

Though not an absolute necessity, it is strongly recommended to have a burn-in of the running time code on the video tape. Negative cutters using DigiConform are encouraged to insist on that.

Time code windows help verifying that a video tape has been loaded properly into the DigiConform system. Internally, DigiConform works with frame counts only. There is no time code input into the system. However, DigiConform can display the video frame count as time code. Thus, making sure that the time code burn-in on the video tape matches the DigiConform frame count throughout the reel is a quick and reliable way to verify that the videotape has been properly loaded into the system.

A video time code burn-in is an essential tool in trouble shooting any discrepancies between the video tape and the cut list.

One easy way to generate a time code burn-in is to record the 'monitor-out' signal of a beta deck to another tape.

No time code is necessary on a dedicated track. DigiConform does not use time code to load the video.

Footage Burn-In in the Avid

If you have trouble getting a video transfer house to make accurate footage burn-ins, you can add the footage burn in the Avid. (It is a bad idea to do that with the video time code.) Here is a work-around that allows adding the footage burn-in in the Avid:

• Get a video tape from your video transfer house that shows a footage burn on black. This tape should be at least as long as your longest reel in the show.
• Digitize this reel into the Avid. Check that every frame number occurs exactly once (+01, +02, +03, etc). If this is not the case you need to digitize with a different pull-in.
• Render your entire reel.
• Create a new video track on top of everything else, and cut the new video on it. Make sure that footage 0+00 is on the academy leader start.
• Apply a resize, picture-in-picture or 3D effect, and crop the video so that it only shows the footage count. Position and scale to taste. This should be a real-time effect.
• You can still add a title on top of this which is also real-time as long as the downstream keyer (DSK) is used.

Negative cutters are encouraged to reject your tape if the numbers don't line up as shown.

Checking the tape for pulldown issues

Checking the output tape is easy, because in a 24 fps project everything happens in a very rigid cadence of 5 video frames and 4 film frames respectively. You only need to examine a couple of seconds of the tape. This is most easily done by digitizing the head of the tape (the academy leader plus a couple of shots) into a 30 fps, single- field project.

Make sure that

• the start mark is only on one frame, not on two.
• the start mark is on a time code ending with :00, and that
• the start mark is on footage 0+00.
• the film frame right after the start mark is on 2 video frames.
• the keycode is in sync with the footage burn-in. Here is what to look at.
• the time code is in sync with footage burn. Starting at the start mark, look for this pattern:

Negative cutters are encouraged to reject your tape if it any of the things listed above does not check out.

For more information, please email mail@digiconform.com.You can also call Rainer Standke at 323 957 0668.