Using the HDMI Output from Nikon DSLR Cameras
One of the most obvious advantages of using an HD-SLR camera system for movie making is the camera’s small and compact size. Add to this the huge number of lenses and accessories available for HD-SLR cameras, and it’s no wonder this camera body has become so popular with filmmakers in such a short amount of time. But did you know some DSLRs also have a feature called HDMI output that lets you get stunning uncompressed video out of your DSLR camera? In this article we explore how to get the best output from your DSLR camera.
The HD-SLR format boasts a large image sensor, capture that yields shallow depth of field, adaptability, small size and relatively low cost—all of which are important requests from today’s filmmakers. These are great production pluses, but the HD-SLR format does have some limitations that require workaround solutions if a filmmaker truly wishes to make the most of production time.
A Difference of File
The most notable difference between HD-SLR cameras and traditional Hollywood cams is the file type footage for each. Hollywood cameras can produce raw video files, a type that allows for the maximum post-production flexibility. Comparatively, footage acquired directly by an HD-SLR (written to an in-camera memory card) is smaller and less data-rich. As technology advances this file type difference may change, but for the time being a filmmaker has options for workaround solutions.
Nikon Senior Technical Manager Steve Heiner addresses this challenge head on. Below, he defines what to expect, offers suggestions for workaround, plus highlights how The Warner Sound was able to send nine videographers into the audience, backstage and on-stage to capture and broadcast live sights and sounds of the annual SXSW Music and Film Festival.
True Raw File Format: Still vs. Motion
One limitation found with any HD-SLR is the camera’s lack of a truly “raw” file format for video capture; raw as compared to what a still photographer may use to acquire maximum file information. For Nikon camera users who shoot stills, the camera raw designation is NEF (Nikon Electronic Format).
High resolution file types created by Nikon HD-SLR cameras include:
NEF: This 12 or 14-bit file size captures maximum information in-camera with no processing of white balance, hue, tone or sharpening done. Other metadata includes extensive image editing capability not available with other file formats. This type of file is converted to a full 16-bit depth when processed into a TIFF file in software such as Nikon’s Capture NX2.
TIFF in-camera: An uncompressed file with full details, no quality loss and 16-bit size. File type can be created in-camera and during post-processing.
JPEG: A file format that offers various levels of compression (Fine, Normal, Basic) to reduce file size. A compressed image is not a total match with the original; minor image detail quality is lost when saved as a JPEG. It is a “lossy” file type.
A raw or NEF image file is either a 12-bit or 14-bit file (depends on the camera). It contains all the raw unprocessed image data collected from the sensor, several small jpeg thumbnails of the image for easy preview, plus an instruction set that tells the computer software how to process the raw images based on the camera’s settings when the photograph was taken. This data is used during retouching and editing to create a finished image with the highest possible quality and the most versatility for image enhancement options.
Unfortunately there is presently no similar raw type movie file for HD-SLR cameras.
To obtain a high bit-depth raw file for motion capture, a cinematographer would need to use a more robust traditional motion capture camera such as an ARRI Alexa or a RED. The trade-off though is that traditional Hollywood cameras are much larger and bulkier. They require very powerful processors that are able to efficiently dissipate the excessive amount of heat generated during filming. As the camera captures, it processes thousands upon thousands of uncompressed frames at high bit levels. And as you probably know, movie industry cameras are also far more costly than an HD-SLR camera.
To Compress or to Not Compress
In the absence of a true raw video file, much can still be done using the HD-SLR native AVC H.264 CODEC files produced by all Nikon HD-SLR cameras. The AVC H.264 CODEC file type is popular on many HD-SLR cameras, as well as some conventional video camcorders. These files typically have a “.mov” file extension.
Understand that the .mov part of the file type is really only the container that houses the movie data. The actual movie data itself may be created using a number of different recording CODECs. A CODEC is the method of encoding (the capture process) and decoding (for playback or edit) of the movie file. Nikon cameras use the AVC H.264 CODEC with additional “B” frame compression for improved image quality without sacrificing the convenience of a modest file size.
The AVC H.264 CODEC provides a clean picture with a relatively modest file size, making it perfect for small-scale video production—as is often the reason for using an HD-SLR. However, the AVC H.264 CODEC uses a high compression ratio so quality can sometimes suffer, as compared to more robust and/or less compressed file types such as ProRes422 (native to Apple’s Final Cut Pro X editing software) or Avid Editing System’s DNXHD files. As a matter of course, AVC H.264 files are automatically transcoded to ProRes files when imported to Final Cut Pro X.
For Nikon HD-SLR cinematographers, there are ways to get the most out of this “baked-in” AVC H.264 compressed file type by utilizing Nikon’s customizable in-camera Picture Control feature. Among the settings Nikon Picture Control governs are adjustments to contrast, saturation, hue and sharpness. One pre-filming consideration is to flatten the contrast curve of the in-camera Neutral Picture Control. Doing this helps maximize the available dynamic range of the file, thereby optimizing it for the post-production process.
Be sure to refer to your camera’s user manual for more information on Nikon’s Picture Control settings. Information shared is essential for getting the most out of your video files.
The Creative Relief Valve: Uncompressed HDMI Output
To help get around the inherent in-camera AVC H.264 compression that’s automatically applied during any movie recording done straight to the memory card, Nikon has developed a high-quality “relief valve” of sorts when using HDMI output.
By connecting many of Nikon’s HD-SLR cameras directly to what is commonly called a “digital video field recorder,” a filmmaker can actually record movie files outside of the camera and direct to an external digital video field recorder. In doing so, the filmmaker bypasses the AVC H.264 data compression required for in-camera capture to memory card.
Working with the AVC H.264 file type for motion capture is analogous to a photographer using the JPEG file type to capture photos. And in parallel comparison, as with a JPEG file type selection, the AVC H.264 dictates that the setting be “baked into the file,” so post-process editing flexibility is more limited.
The decision to bypass in-camera record (go direct to memory card) can therefore actually benefit the overall post-production process. The addition of an external field recorder gives the filmmaker latitude to produce in exactly the file type required for a specific edit program—for instance ProRes files for Final Cut Pro X or DNXHD files for the Avid. To further illustrate, if a filmmaker is using Apple’s Final Cut Pro X, most field recorders can write a ProRes file (native to Final Cut Pro X). Some recorders can also write a DNXHD file (native to the Avid system).
Quality Trade Off: Recording In-Camera vs. Using External Device
Obtaining superior quality footage may seem the obvious choice when producing, but this might not always be a director’s top objective. Precisely how much trade-off ensues as a result of the file recording method was tested by Nikon and several prominent filmmakers.
A comparison was made between the two methods: direct-record to an in-camera memory card with AVC H.264 compression applied vs. Live View direct to a field recorder (testing both ProRes and DNXHD file types).
When viewing files, the pros noted quality differences but the differences were not always enough to warrant the added hassle of attaching a field recorder—especially in situations where it would present more of a burden than a benefit. Opting for slightly lower quality is sometimes outweighed by a need to keep the camera package light and mobile. Some pros also prefer to work without additional plug-in devices, especially anything that requires its own power source, memory cards or hard drives.
Another less obvious advantage to using a field recorder-plus-HDMI-port is that you are no longer limited to short filming sequences. With present technology, a 20-minute limit exists when recording to a memory card at the highest quality level in a Nikon HD-SLR.
For shooting interviews, performances or any other activity that spans a long period of time, the advantage of a separate field recorder is that your clip length is only limited by the capacity of the hard drive(s) paired to the recorder. You also have the option to use either spinning media or the newer solid state media drives. Solid state media offers the advantage of no moving parts and is often a better choice for cameras that are in motion during recording.
Another rather innovative and unusual use for the HDMI port on our HD-SLR cameras came to fruition when Nikon teamed with The Warner Sound.
During the 2012 and 2013 SXSW Music and Film Festival in Austin Texas, a total of nine D4 HD-SLR bodies, plus various lenses, were used to record dozens of live music performances over a three day period. This recording activity included live broadcasting to The Warner Sound YouTube channel. What was unprecedented was that HD-SLR cameras were pivotal in streaming live broadcast of music performances directly to end users via YouTube. This would not have been possible without the HDMI output capability of Nikon HD-SLR cameras.
All HDMI signals from the nine on-site cameras were fed into a live switching console. A director and operator would call-out which camera feed was desired at each moment throughout the entire three nights of performances—providing an instantaneous broadcast that offered tremendous footage with look and feel that’s unique to a large sensor HD-SLR camera.
Signals from all nine cameras were also concurrently recorded to external field recorders so that the content could be used again and again for rebroadcast and future editing.