Drop Frame vs. Non-Drop Frame, Explained

As media editors, it’s important that we understand the difference between drop frame and non-drop frame timecodes, their respective benefits, how each method works, and when they should be utilized. To help keep your workflow running smoothly and maximize the benefit of adding Sonix subtitles or captions, it’s essential to have a solid working knowledge of both. 

Drop frame vs. non-drop frame timecode considerations are often cited as one of the most confusing topics in video production. But they don’t have to be. In this article, we’ll provide clear definitions of drop frame and non-drop frame timecodes, how they work, and how timecodes affect captioning and subtitles. 

What is Timecode?

Timecode is a precise way of counting and labeling the frames in a recording so you know their exact location. Think of video timecodes like URLs on the web. When you browse the internet, you don’t pay attention to the address of the page you are on. However, if you want to communicate anything about that page, you need the URL to share the exact location. Timecode does exactly this but for video frames, and is used to reference and synchronize all types of audio-video files. 

SMPTE timecode is the standard for labeling video and film. It was developed in the 1960s by the Society of Motion Picture and Television Engineers (SMPTE) to allow accurate editing, identification, and synchronization of media. SMPTE timecode is typically expressed in HH:MM:SS:FF format (hours, minutes, seconds, frames). Hours, minutes and seconds are numbered like a regular clock. Seconds are divided up into frames, which are single images. 

The two main things you need to know about timecode before we progress further are that:

1. Only whole, not fractional, frames are counted.
2. Numbering is zero-based, meaning the first frame is counted as 00, not 01.

The Evolution of Timecode

While most web video content is referenced in real-time code, the situation is more complex in broadcast video. When television was invented, fps (frames per second) were based on the electrical system of the time. Since all broadcasts were live and not recorded, the only way to synchronize the studio film cameras with viewers’ television sets at home was to use the electrical mains. The United States – and subsequently all National Television Standards Committee (NTSC) locations – use 60Hz as a base, whereas Europe – and therefore all Phase Alternate Line (PAL) locations – use 50Hz as a base. 

Originally, all video was black-and-white at 30fps, with no option for color broadcast. When color television was introduced in 1953, the NTSC standard was modified to accommodate color in the existing black-and-white receivers, creating a subcarrier that minimized interference. The frame rate was reduced from 30fps to 29.97fps, resulting in a disparity between real-time and video time. 

Today, timecode formats are still numbered as if they were 30 frames per second. In other words, ff is a number from 00 to 29. As we know, timecode only accounts for full frames. So, if your frame rate is 29.97fps, the next timecode after HH:MM:01:29 would be HH:MM:02:00. That means that in 100 seconds, there will only be 2997 frames rather than 3000. This creates a lag, because after 60 real-time minutes, a video playing at 29.97fps will read only 00:59:56:12. So adjustments are necessary to accurately map to real time. 

That’s where drop frame comes in. 

Drop Frame vs. Non-Drop Frame: What’s the Difference? 

Both are methods for measuring video frames against time. The difference is that drop frame matches real-time, whereas non-drop frame does not. The fact that non-drop frame timecode is not accurate with respect to real-time is the very reason why drop frame timecode was created. After all, a broadcaster must know the exact length of their program so they can schedule their broadcast with commercials to match real-time throughout the day. If audiovisual media was produced in non-drop frame timecode, they would quickly find themselves in trouble. 

To put it more simply, it helps define each method by primary function:

• What is drop frame used for? Telling time. Reading a drop frame timecode tells you exactly where you are in terms of a chronological clock (think of drop-frame timecode as “time elapsed” on your video), but not how many frames have gone by. 
• What is non-drop frame used for? Counting frames. It is “frame-accurate”, meaning it correctly counts the number of frames in one second. However, in NTSC video, 30 non-drop frames do not equal one second of time. 

What is Drop Frame Timecode? 

Drop frame timecode, often abbreviated to DF, was introduced as an attempt to fix the disparity with 29.97fps video and make it match real time. Since timecode can only count whole frames, there should be 108,000 frames per hour (30fps x 60 seconds x 60 minutes). However, since NTSC runs at 29.97fps, 0.03 frames are unaccounted for every second, meaning a total of just 107,892 frames per hour (29.97fps x 60 seconds x 60 minutes). The total discrepancy is 108 frames, or 3.6 seconds (108 frames/30fps), meaning a real-time hour of video at 29.97fps would show on the timecode as 01:00:03;18.

So how does one fix the discrepancy? Rather than trying to match timecode to frames, utilizing DF effectively leads to a drop in frame numbers. It doesn’t actually drop any frames, of course. It simply stops counting the frame labels. More specifically, it drops a frame number every time the remaining 0.03 of a frame adds up to a full frame, which is once every 33.33 seconds. So in one hour, drop frame video removes 108 frame numbers from the total count so that the 29.97 fps video will finish in real-time at 01:00:00;00.

However, rather than dropping all 108 frame numbers once an hour, or even 18 frame numbers once every 10 minutes, there is a specific pattern that drop frame timecode follows. The first two frame numbers are dropped from every minute, with the exclusion of every tenth minute. In other words, frame numbers are dropped from minutes 01-09, 11-19, 21-29, 31-39, 41-49, and 51-59. However, frame numbers are not dropped in minutes 00, 10, 20, 30, 40, or 50. By the time one hour of footage has elapsed, 108 frame numbers have been removed from the count, so the counter is adjusted to compensate for video playing back at a rate of 29.97fps rather than 30fps.

It is important to remember that drop frame timecode simply removes numbers from the count, and does not remove any actual frames so your recording itself is unaffected, regardless of whether you use drop frame vs. non-drop frame. 

What is Non-Drop Frame Timecode?

Thankfully, non-drop frame timecode, often abbreviated to NDF, is significantly more straightforward. It counts every single video frame without any relabeling, so the ratio of timecode recording to frame count is 1:1. However, a problem arises with NSTC’s standard playback rate of 29.97fps because it means an hour-long recording in non-drop frame is not an hour in real time. It is, in fact, 3.6 seconds shorter. That’s because it’s counting 3000 frames per 100 seconds when the play rate is really only 2997 frames per 100 seconds. The result is that a 1 hour program using a non-drop timecode will end at 00:59:56:12, rather than 01:00:00:00.

Choosing Between Drop Frame and Non-Drop Frame

Since neither drop frame nor non-drop frame timecodes alter the visual image in any way, you may be wondering why your choice of drop frame vs. non-drop frame even matters. Neither format is better than the other when it comes to editing, and most systems can now deal with multiple formats and frame rates. The truth is you can shoot and edit in either, and even switch between them – although it’s a lot easier to be consistent. Most of the time, the choice will be dictated by your editing system, distribution media, or simply the video editor’s preference. However, as a general rule, if the production is intended for broadcast, it’s standard practice to use a drop frame timecode.

Not sure which format you’re looking at? It’s easy to determine which timecode is being used. Non-drop frame files use all colons (HH:MM:SS:FF) whereas drop frame files use a semicolon or a period between the seconds and the frames (HH:MM:SS;FF or HH:MM:SS.FF).

How Drop and Non-Drop Frames Affect Transcription & Captioning 

If you’re not already closed captioning your video content, it’s time to start. Firstly, it’s a recommended best practice for digital accessibility as recommended in the Web Content Accessibility Guidelines (WCAG). Also, subtitled videos consistently rank higher than those without subtitles because they get more engagement in terms of comments, likes and shares.

When captioning your video, it’s important to know whether your file is drop frame or non-drop frame so that your captions are synched accurately with the timing of the media. If you caption a drop frame video with non-drop frame captions, nothing will be synched and the lag will get worse as time goes on. This problem is easily avoided with Sonix advanced, cloud-based software. Sonix can automatically sync your subtitles to your video’s timecode, allowing you to manually adjust your subtitles to perfection.

Hassle-Free Transcription with Sonix

Sonix is the world’s best multi-language, automated transcription and subtitling platform. Featuring more than 35 languages, it offers fast and highly accurate transcripts at an affordable price. 

Already a top choice among industry professionals, the intuitive and easy-to-use dashboard can deal with multiple types of file input. And, of course, Sonix can handle timecodes in both drop frame and non-drop frame. Premiere and Audition from Adobe and Final Cut Pro are all possible destinations for your completed transcript export. 
Sonix makes it easy to add subtitles to videos. Contact us today to begin your free trial, and never have to worry about drop frame vs. non-drop frame in your transcriptions again.