The concept of using an external device to record video is virtually as old as the concept of video itself. In their earliest form, portable video recorders took the form of large, heavy backpacks powered by a lead-acid battery belt, both worn by the camera operator. Even at this size portable recorders only offered what today would barely be considered standard definition resolution.
Fortunately for camera operators the current crop of 4K video recorders are a mere fraction of the weight and far more power efficient than external video recorders of the past. Even with this dramatic weight loss it may seem curious that at a time when onboard recording is an almost universal feature of camcorders, external recorders are still being used in video production. To satisfy this curiosity one must look at the current state of 4K technology and 4K camcorders.
It is a contradiction in terms that several professional 4K camcorders, like the Canon C500 and Sony FS700, cannot record 4K video using their built-in recorders. Camcorders in this category include sensors offering 4K resolution, 4K image processing capability, and 4K outputs. However, onboard recording for these camcorders is actually limited to only HD or 2K resolutions.
Still, other professional 4K camcorders, like the FDR-AX1, can actually record 4K video onboard, but do so onto consumer grade media using high compression rates. These techniques to reduce bandwidth introduce visual artifacts, while inexpensive media increases the chances of corrupted or lost files. To overcome these limitations many users find themselves turning to external 4K video recorders to get the most out of their 4K camcorders.
The defining aspect of a 4K recorder can be stated simply as the capability of recording a horizontal resolution of approximately 4000 pixels. This is more than four times the resolution of high definition and over 16 times that of standard definition. As impressive as this may seem, there is more to these recorders than just greater resolution capability; 4K recorders often offer the advantages of RAW recording, higher bit-depth color, and less compression over the onboard recording systems of many 4K camcorders.
In addition to improving recording quality many current recorders also offer monitoring and feedback capabilities such as waveform monitors, LUTs (Look Up Tables), and vectorscopes—features not found within many camcorders. A recorder may also be used as a backup to the in-camera recording, offering a greater degree of reliability or the flexibility to hand off an immediate copy to the post production team so they can begin working with the footage. Whatever the purpose or appeal, external 4K recorders have found their place in all levels of 4K video production today.
Anatomy of a 4K Recorder
All current 4K recorders rely on removable media. This media usually comes in the form of proprietary SSDs or proprietary memory cards. By using proprietary media, manufacturers can control the quality and reliability of the flash memory being used, thus ensuring a sufficient level of performance when recording high-bandwidth 4K data streams. With the sheer volume of bandwidth needed to record 4K at higher frame rates, some recorders can record to two SSDs simultaneously.
The primary value of an LCD or OLED screen on a 4K recorder is to monitor the video image being recorded. Many of these screens are touch sensitive, allowing users to access the recorder’s menu system and controls. Screens on some 4K recorders offer the added benefit of video analysis tools like waveform monitors, vectorscopes, focus assist tools, audio monitoring, etc.
Formats and Codecs:
While neither formats nor codecs are a physical component of 4K recorders, they are perhaps the most important decision one should consider when choosing a 4K recorder. The formats supported by a recorder define which cameras are compatible with that particular recorder. The recorded codec or format chosen will also define much of the post-production workflow. Some recorders offer codec or format licenses that can be purchased permanently or rented for short periods of time as needed.
Video inputs define the connectivity and, in many ways, the compatibility of a 4K recorder. Most cameras that can output 4K do so over BNC cables as a proprietary data stream. This means there is no single standard for 4K video signals. 4K signals used in recorders fall into one of the following categories:
- 2 x BNC - Uncompressed RAW
- 1 x BNC - Compressed RAW
- 1 x BNC 6G SDI
- 2 x 3G HD-SDI
- 4x 1.5G HD-SDI
4K video outputs serve the purpose of allowing the director, cinematographer, or other interested parties to run video out to a larger monitor or display live or after the shot is complete using a playback function. 4K video output signals are offered in the form of SDI (1 x 6G, 2 x 3G, 4 x 1.5G), or 4K HDMI.