Using the DVCPRO HD Frame Rate Converter

Some 720p DVCPRO HD camcorders can record at variable frame rates, a feature once exclusive to film cameras.

In film, the traditional frame rate is 24 fps, but many cameras can be “overcranked” or “undercranked” to achieve slow- and fast-motion effects. The technique is straightforward: the more frames you record per second, the longer it takes to play them back at 24 fps, and therefore the slower the motion onscreen. The reverse is also true: the fewer frames you record per second, the faster the motion when played back at 24 fps.

Shooting for Slow-Motion and Fast-Motion Effects

Variable frame rate recording with DVCPRO HD works the same way it does with film, except that the final playback rate varies (24, 25, 30, 50, or 60 fps) depending on your final output format. During shooting, you need to have an intended playback rate in mind to know what frame rate to record your footage at. For slow-motion effects, you need to record at a frame rate higher than your intended playback rate. For fast motion, shoot at a frame rate lower than your intended playback rate.

For example, if you shoot at 60 fps and play back your footage at 24 fps, the result will be slow motion because the rate at which you recorded was higher than the final playback rate. However, if you record at 24 fps and play back your footage at 24 fps, your footage will play at normal speed.

How DVCPRO HD Variable Frame Rate Recording Works

In 720p DVCPRO HD variable frame rate recording, the camera CCD outputs a frame rate while the recording rate is fixed at either 59.94 fps or 50 fps (depending on the camcorder model).

A 720p60 camera CCD can generate between 4 and 60 images per second, while the recording unit records at a constant rate of 60 fps (technically, 59.94 fps). When you select any frame rate lower than 60 fps, some images from the CCD are recorded more than once. These redundant frames are tagged for later removal using a special device called a frame rate converter.

What Is a Frame Rate Converter?

A frame rate converter, or FRC, is hardware or software that converts the frame rate of your footage by:

  • Setting the rate of playback higher or lower, so that each frame lasts a longer or shorter amount of time on the screen. By changing the duration that each frame is shown onscreen compared to its recorded duration, you can speed up or slow down the action in your media.

  • Intelligently skipping redundant frames containing variable frame rate flags

Some frame rate converters can also do upconverting and downconverting, allowing you to use 720p for variable speed cinematography and then transfer to 1080i or 480i (standard definition).

How a Frame Rate Converter Works

On tape, variable frame rate video footage may look a bit strange—almost stroboscopic—because many frames are repeated with the intention that they will be removed. Once the frame rate converter removes the duplicate frames and only unique frames remain, your footage plays back at the intended rate.

For example, if the camera is set to record 15 fps, three out of every four frames are tagged as duplicates, and the frame rate converter ignores or discards them. The frame rate converter then converts the 15 fps footage to a new media file at a standard frame rate such as 23.98, 29.97, or 59.94 fps.

Several examples of 720p60 DVCPRO HD variable frame rate footage are shown below.

Figure. Diagram showing how the frames in 1 second of 60 fps 720p DVCPRO HD video are tagged for duplicate frame removal when you record variable frame rate video.

You can record variable frame rates with a 720p50 camcorder just as you would with a 720p60 camcorder, although the range of variable frame rates is between 4 and 50 fps.

About Native Variable Frame Rate Recording

Camcorders such as the Panasonic AG-HVX200 and AG-HVX200E aren’t limited by the constraints of tape-based recording, so they can record native frame rates without duplication of frames. For more information, see 720pN DVCPRO HD Native Frame Rate Recording.

If you record variable frame rates in these native frame rate modes, the camera can display the results immediately without the use of a frame rate converter. For more information, see the documentation included with the Panasonic AG-HVX200 camcorder.

About the DVCPRO HD Frame Rate Converter

The DVCPRO HD Frame Rate Converter in Final Cut Pro provides conversion options formerly available only with expensive hardware. You can use the Frame Rate Converter to create an output movie with a frame rate different from the original frame rate (for example, convert 59.94 fps footage to 23.98 fps).

The Frame Rate Converter can create a new self-contained QuickTime movie or create a QuickTime movie that actually refers to the frames of the original media file while playing them back at a different rate.

The Frame Rate Converter only works with certain 720p DVCPRO HD formats and does not process timecode or audio.

Original Media File Requirements

The Frame Rate Converter only processes media files that meet the following requirements:

  • The media file must use the DVCPRO HD 720p60 or DVCPRO HD 720p50 codec.

  • The media file must be captured or ingested at a frame rate of 59.94 or 50 fps.

To ensure that your media file contains the variable frame rate footage from the camera, make sure that you are using a capture preset with the Remove Advanced Pulldown and/or Duplicate Frames During Capture From FireWire Sources checkbox unselected. For 720p60 footage, the easiest way to ensure you retain proper flags is to capture footage using the DVCPRO HD - 720p60 capture preset.

Timecode and Audio Restrictions

The Frame Rate Converter does not include timecode or audio in the processed media file. Although this may seem like a limitation, it is important to remember that the primary purpose of timecode is to link your clip back to particular timecode addresses on a videotape for recapturing. Because the frames of the processed media file do not exactly correspond to the frames on the original tape, including the original timecode would only lead to confusion. It’s best to consider your processed variable frame rate media file as a completely new piece of media.

Audio is not affected or considered when shooting variable frame rate footage. Just as with variable frame rate film cinematography, these shots are usually recorded MOS (without sound), and sound is added later during post-production.

About the Frame Rate Converter Options

The options for the Frame Rate Converter are described below.

Figure. DVCPRO HD Frame Rate Converter.
  • Remove Duplicate Frames: If the Remove Duplicate Frames checkbox is selected, the Frame Rate Converter removes any flagged duplicate frames when creating the new file or processing the existing media file (depending on whether the Make Self Contained File checkbox is selected).
  • Make Self Contained File: If this checkbox is selected, a new self-contained QuickTime media file is written to disk. Select this option if you want the new media file to be completely independent of the original file. You may want to do this if you plan to get rid of the original file, or if you want to copy the new, processed file to another editing system.

    Note: If you create a self-contained file, you need to have enough disk space for another copy of the media file.

    If this checkbox is unselected, a QuickTime reference movie is created. A QuickTime reference movie refers to frames in the original media file. Reference movies are very small relative to the original media file because they don’t actually contain any media (in the same way that a Final Cut Pro project file is small because it doesn’t contain any of the media that it refers to). The disadvantage of this option is that reference movies still require the original media file.

    For more information, see “Exporting QuickTime Movies” in the the Final Cut Pro 7 User Manual.

  • Import Result Into Final Cut Pro: If the Import Result Into Final Cut Pro checkbox is selected, the resulting media file is imported into the current project. The imported clip uses the name you enter in the Save Converted Media dialog.

Using the Frame Rate Converter

The Frame Rate Coverter processes the source media file and creates either a new, independent file or a reference file for the movie.

To convert a DVCPRO HD media file using the Frame Rate Converter
  1. Select a clip in the Browser that meets the Frame Rate Converter requirements (see Original Media File Requirements).

  2. In Final Cut Pro, choose Tools > DVCPRO HD Frame Rate Converter.

  3. Select options for processing the media file.

    For more information about the options, see About the Frame Rate Converter Options.

  4. Click OK.

  5. In the Save Converted Media dialog, enter a filename, navigate to a location, then click OK.

The Frame Rate Converter first processes the source media file, removing tagged duplicate frames (if the Remove Duplicate Frames option is selected). The Processing Source Media progress dialog appears to show the status of processing.

Once processing is complete, the final converted movie file is written to disk as a new, independent file (if the Make Self Contained File checkbox is selected) or as a reference movie file pointing to the relevant frames of the original media file.

If the Import Result Into Final Cut Pro option is selected, the converted media file is imported into Final Cut Pro. The clip name is the same as the name you entered in the Save Converted Media dialog. Note that the converted media filename and the resulting clip name are typically not the same, so you need to be especially organized when managing media files created by the Frame Rate Converter.