Telecine, Pull-Down, and Reverse Telecine

The following sections describe methods for embedding and extracting 24p video in different formats. Some of these techniques are based on existing film-to-video methods, and some are newer approaches. The basic technique for transferring film to video, called telecine, uses a process called pull-down to map 23.98 fps film to 29.97 fps interlaced video. Once the video is captured on disk, software can perform reverse telecine, or reverse pull-down, to restore the original 23.98 fps film frame rate.

In progressive digital video systems such as 720p60 DVCPRO HD video, a similar process can be performed in-camera to map 23.98 fps to 59.94 fps, but entire frames are duplicated instead of fields. During or after capture, the duplicate frames are removed. A camcorder or deck that performs duplicate frame insertion can add metadata (known as flags) that inform software when to remove or ignore duplicate frames.

Note: Pull-down refers to the addition or removal of fields, not duplicate frames.

Standard 3:2 Pull-Down

Also known as 2:3:2:3 pull-down, this is the standard telecine method of transferring film to NTSC video. The film is slowed by 0.1 percent (a factor of 1000/1001) from 24 fps to 23.98 fps, and then each film frame is transferred to interlaced video in a repeating 2:3:2:3 field pattern.

In the illustration below, film frames A, B, and D are mapped to video frames 1, 2, and 5. However, because film frame C is split into two fields across video frames 3 and 4, pull-down removal requires deinterlacing, which is more processor-intensive than removal of pull-down patterns such as advanced (2:3:3:2) pull-down.

Pull-down removal typically requires manual identification of the A frame in the pattern, which you can identify visually by moving frame by frame through your footage until you recognize the pull-down pattern.

Figure. Diagram showing how 1 second of 23.98 fps film frames map to the frames in 1 second of 29.97 fps video when 3:2 pull-down is applied or removed.

If you edit 3:2 pull-down footage without removing the pull-down first, you need to be particularly careful to match the five-frame pull-down cadence at every edit. Edits with broken cadence, such as a repeating or out-of-order frame (for example, A, B, A, B, C, D) can confuse reverse telecine operations. In general, you should avoid editing 29.97 fps pull-down footage. Instead, remove the pull-down of your footage first, edit at 23.98 fps, then reinsert pull-down during output.

Several NTSC and 1080i60 HD camcorders can record using standard pull-down, though advanced pull-down is usually recommended when recording 24p video. However, for final playback on television or DVD, 3:2 pull-down is generally considered to have the most acceptable quality of motion.

2:3:3:2 Advanced Pull-Down

Camcorders such as the Panasonic AG-DVX100, the Panasonic AG-HVX200, and the Canon XL2 use this method to store 23.98 fps video within interlaced 29.97 fps footage. Video frames 1, 2, 4, and 5 in the pull-down pattern represent film frames A, B, C, and D. Removing advanced pull-down is more efficient than removing standard 2:3:2:3 pull-down because no deinterlacing is required.

To remove advanced pull-down, video frame 3 in the five-frame pattern is simply discarded during capture or ignored during playback.

Figure. Diagram showing how 1 second of 23.98 fps frames map to the frames in 1 second of 29.97 fps video when 2:3:3:2 pull-down is applied or removed.

Another feature that makes advanced pull-down removal more efficient is the insertion of “flags” in the video signal that can be used by software to automatically detect which frames must be removed. This makes advanced pull-down an automatic process compared to the manual cadence identification usually required to remove 3:2 pull-down.

Despite its efficiencies, the advanced pull-down pattern is not as aesthetically pleasing as 3:2 pull-down. If you plan to finish your project at 23.98 fps, advanced pull-down is usually the best choice. However, if you plan to output your final 24p project to 29.97 fps interlaced video, you may want to add 3:2 pull-down because its pattern is considered to be more visually appealing.

2:2:2:4 Pull-Down

This is an efficient but low-quality playback option used for previewing 23.98 fps footage on an NTSC monitor. Few systems can reverse this kind of pull-down, so you should never record footage with this kind of pull-down. This option is available for situations when processing power is at a premium and your system is unable to generate 2:3:2:3 pull-down or advanced pull-down during playback.

Figure. Diagram showing the 2:2:2:4 pull-down pattern.

720p DVCPRO HD Duplicate Frames

720p DVCPRO HD camcorders can record 24 fps footage within a 60 fps signal by duplicating frames. The duplicate frames are usually flagged within the DVCPRO HD video signal so applications like Final Cut Pro can automatically remove them. You can also remove duplicate frames using a frame rate converter (such as the DVCPRO HD Frame Rate Converter in Final Cut Pro).

The duplicate frame pattern used in 720p24 footage is similar to the standard 3:2 NTSC telecine pull-down pattern, but there is no interlacing because 720p video is progressively scanned.

Note: 720p footage is almost always 23.98 fps, but true 24 fps recording is also possible on particular camcorders.

Figure. Diagram showing how duplicate frames are inserted to record 23.98 fps footage within a 59.94 fps signal and how the duplicate frames are flagged for removal.

Progressive Segmented Frame Recording

Sony CineAlta cameras can record 23.98 or true 24 fps Progressive segmented Frame (PsF) footage on HDCAM or HDCAM SR tape. The camera records at 48 fields per second while each progressive frame is placed on two fields, resulting in 24 fps.

Figure. Diagram showing how the frames in 1 second of 23.98 or 24 fps progressive video map to the fields in 1 second of 23.98 or 24 fps interlaced video.

24 @ 25

True 24 fps film or video can be transferred to PAL (25 fps) by speeding up the frame rate by 4 percent. For film editing purposes on PAL video, applications like Cinema Tools can slow the 25 fps PAL video back to 24 fps (a process called conforming) so that sync is maintained with the original audio.

For showing film-originated movies on PAL video, both film and audio speed are increased by 4 percent. The speed increase is considered acceptable, although the audio must be “pitch shifted” down to match the original. This is the most common method for film-to-PAL transfers.

Figure. Diagram showing how the frames in 1 second of 24 fps film compare to the frames and fields in 1 second of 25 fps PAL video when the original frame rate is sped up by 4 percent.

24 @ 25 Pull-Down

This method does not change the speed of the original film. Instead, film frames 12 and 24 are pulled down for a duration of three fields instead of two, creating a subtle stutter each half second. This pattern is technically described as 2:2:2:2:2:2:2:2:2:2:2:3 pull-down.

Figure. Diagram showing how the frames in 1 second of 24 fps film compare to the frames and fields in 1 second of 25 fps PAL video achieved by 24 @ 25 pull-down.

24 @ 25 Repeat

This method simply repeats every 24th frame once to fit 24 fps footage into 25 fps. This causes a noticeable stutter every second but requires less processing than the 24 @ 25 pull-down pattern because no special interlacing is required. This pull-down pattern is analogous to the NTSC 2:2:2:4 pull-down pattern in the sense that it requires the least amount of processing power but results in the most noticeable stutter. You should use this option for preview purposes only and avoid it for final output.

Figure. Diagram showing how the frames in 1 second of 24 fps film compare to the frames and fields in 1 second of 25 fps PAL video achieved by repeating the final frame of each second.

Native 24p

Some video camcorders that record to file-based media can record at 24 or 23.98 fps. For example, the Panasonic AG-HVX200 can record 23.98 fps footage directly. Digital cinema cameras such as the Panavision Genesis, the Dalsa Origin, and the RED ONE can record natively at 24 fps. Of course, film is also recorded at 24 fps.

Figure. Diagram showing the frames in 1 second of 23.98 or 24 fps footage.