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How to Use Drop Frame or Non-Drop Frame

By Shawn Amaro

Understanding the basics of drop frame (DF) and non-drop frame (NDF) can help keep your work flow running smoothly. B&H Photo Video understands the multitude of video formats that can be used in a single project; this article will hopefully clear up some of the confusion caused by the concepts of frame rate, broadcast standards, and accuracy involving timecodes. Drop frame and non-drop frame were created before High Definition (HD), but the same rules still apply.

Timecode is used to provide search ability on your tapes, disks, and other media. It measures time in Hours:Minutes:Seconds:Frames and creates a distinct identifier for each frame, based on the HH:MM:SS:FF format. Every frame is given a unique timecode number, making it easily found by a non-linear or linear device that utilizes and reads timecode. You can find out more about timecode in a previous article on the B&H web site, Understanding TIME CODE- part I By Robert Morton & Jack Fettman.

Drop frame and non-drop frame timecode do not alter the visual image in any way. No frames or images are lost in drop frame; it is simply a way of labeling every frame. They are methods of counting. If two projects were created with identical cuts, both timelines in the software would be identical. Since this does not affect the picture, choosing between drop or non-drop frame can be determined by the specifications of the editing system, distribution media, or video editor’s preference. Understanding frame rate helps us understand why these two methods exist.

Frame rate is the measurement of individual images, known as frames created by an imaging device. Originally, black and white video ran at a true 30 fps (Frames per Second). Color video required that the frame rate be slowed to 29.97 fps, due to the physical limitations of the black and white circuits in older television sets, and issues involving sound waves. It's this slowdown of frames that causes the disparity between real time and the measurement of video time.

The 29.97-second frame rate does not divide into one second as easily as 30 fps does. Since creating a fraction of a frame is impractical, a method of counting and adjusting full frames is necessary. Drop frame timecode counts each video frame. When the remaining .03 second of 29.97 finally adds up to a video frame, it drops a frame number. It does not remove a frame.

Moving the decimal place over from 1.8 frames per minute produces 18 full frames for every 10 minutes. These frame numbers are dropped over time instead of all at once. The distribution of those 18 frames equals about 2 frames (:00 and: 01) a minute, but no frame numbers are dropped in the 10th minute because the process has started over. There are never any frame numbers dropped when the minute is divisible by 10.

This means ten minutes in drop frame 00:10:00:00 is the same as 00:10 minutes in real time. Remember, you are not losing frames. The way they are being counted has been changed. 2,997 full frames are presented every 100 seconds. If you are cutting a scene using drop frame time code, the duration of 60 minutes is exactly 60 minutes and 0 frames. Drop frame is a standard for broadcast networks using NTSC due to this correlation with real time.

Non-drop timecode counts every single video frame and doesn't re-label any frame to account for the 29.97 fps. This means that if you have a 60-minute film and 0 frames in non-drop frame timeline, it is not the actual running time of the film. This makes non-drop lengths shorter than the real time. It is counting 3000 frames per 100 seconds when it's really 2997 frames per 100 seconds. A program using non-drop timecode is approximately four seconds shorter per every hour. 60 minutes of non-drop frame format will be 108 frames lower, making it 00:59:56:12 at the end of a real time hour 01:00.

One format is not better than the other when it comes to your editing system. Editing systems can now accept a myriad of formats and frame rates. Your camera person can shoot in 24 fps and you can capture in 30 fps drop frame or non drop frame. You can even toggle between drop frame and non-drop frame in most non-linear timelines. Check your manual for the correct way to switch between both.

An Adobe Premiere Pro CS3 user can switch between drop frame and non-drop frame. You can select the timeline window to make it active. While in the title bar, choose Window > Window Options > Timeline Window Options. Within the Timeline Window Options dialog box, select 30 fps Non-Drop Frame Timecode or Drop Frame and click OK. This process is similar in other editing systems.

Though most non-linear systems can handle drop frame and non-drop frame, capturing from tapes recorded with both drop frame and non-drop frame timecode may produce unexpected results. You will be unable to export a correct EDL or XML file, re-capture footage or use media management software when inaccurate timecode occurs. While working with tape containing both non-drop and drop frame timecode, stay away from any forms of batch capture. Capture each section individually to prevent timecode problems. You may want to label each section as a different tape and mark your original master with the changes.

You could also use a frame synchronizer to adjust the rates for different mediums even without a non-linear system. The AJA FS1 Frame Synchronizer and Bi-directional Converter is a universal SD/HD audio/video frame synchronizer and converter. This converter offers “everything in, everything out” architecture. The FS1 can work simultaneously with both HD and SD video for broadcast-quality video and 24-bit audio. The FS-1 can up- or down-convert between SD and HD, and provide simultaneous HD and SD outputs. Cross-conversions between HD formats are also supported, with simultaneous output of both formats.

The Aja FS1 Frame Synchronizer
The Aja FS1 Frame Synchronizer

Sometimes people will refer to 29.97 fps as “30 fps,” which can cause confusion. Problems may occur any time source footage is captured at the wrong frame rate. It is better to be accurate and write NTSC (ND or NDF) than to refer to “30 fps.” Most professionals will know all NTSC is 29.97, but accuracy can prevent mistakes. PAL countries do not experience this issue since the video frame rate is always 25 fps. The high-definition (HD) formats follow the same rules as standard definition and are listed below.

Format specifications

SMPTE (Society of Motion Picture and Television Engineers)

29.97 fps

NDF

Color

60Hz

Non-Real Time

29.97 fps

DF

Color

60Hz

Real Time

30 fps

NDF

Black & White

60Hz

Real Time

59.94 fps

NDF

Color HD

60Hz

Non-Real Time

59.94 fps

DF

Color HD

60Hz

Real Time

60 fps

NDF

Color HD

60Hz

Real Time

EBU (European Broadcasting Union)

25 fps

NDF

Color

50Hz

Real Time

50 fps

NDF

Color HD

50Hz

Real Time

Film

24 fps

NDF

Color

N/A

Real Time

23.98

NDF

Color HD

60Hz

Non-Real time

Hopefully, this article has cleared up some of the confusion caused by frame rate, broadcast standards, and accuracy involving both drop frame and non-drop frame timecode. Just remember that NTSC video always runs at 29.97 fps and can be notated in drop frame or non-drop frame. Drop frame timecode only drops numbers referring to frames, and not the frames themselves. Knowing which format to use to capture and export your footage will make for a smooth work flow, allowing you more time for creativity.

 

Please email feedback on this article, or suggestions for future topics, to videofeedback@bhphotovideo.com