Render Errors

Symptom #1: Red Render Lines in 24P Sequences

"I keep getting red render lines in my 24P sequences. Which frame rate is correct?"

Background

The generic term 24P, when used with DV, DVCPRO, and certain HD formats, is actually something of a misnomer. 24P footage recorded on DV-NTSC is always 23.98 fps recorded with a pulldown at 29.97 fps. Even 23.98 fps is something of a misnomer, because it is a contraction of 23.976 fps. Because 23.976 is a mouthful, editors commonly refer to it as "twenty-three nine eight." This should not confuse you too much, but it is rather important to understand. Some formats, such as Panasonic's DVCPRO HD, can use variable frame rates from 23.98, 24, 30, and 60.

Because DV NTSC runs at 29.97 fps rather than an even 30 fps, it is known as a noninteger frame rate. It is difficult to perform a pulldown of the solid integer film rate of 24 fps into 29.97 evenly. The standard cadence of 2:3:2:3 doesn't quite fit. Because we are working with digital video frames, it's relatively easy for the technology to slow the frame rate of the recorded video slightly to make an even ratio similar to the ratio between 24 and 30. Thus, to match NTSC's true rate of 29.97, a rate of 23.976 is used.

Capture settings must match the footage on the tape; then the sequence settings must match the captured clips' settings. 24P footage from DV cameras always uses a 23.98 fps frame rate pulled down into 29.97 (rather than 24 fps pulled down into any variation of NTSC). Because it is pulled down into NTSC 29.97 fps, you can either capture it normally and remove the pulldown manually or have FCP or a third-party capture device remove the pulldown automatically.

Solution

After capture and removal of the pulldown, you can edit the clips only in a 23.98 sequence. If you attempt to edit the media in sequences with other editing timebases, you will see a red render line. Likewise, if you do not remove the pulldown, either manually or automatically, you will get a red render line unless you insert the clip in a 29.97 sequence.