Convergent Gemini 4:4:4 HD & RAW Recorder

Gemini 4:4:4 Recorder with ARRIRAW support

  • Description
  • Rates & Packages
  • Case Studies
  • Other Information

Gemini 4:4:4 Uncompressed HD Recorder

Uncompressed 4:4:4  HD Recorder designed for cameras with dual HD-SDI output capability, 3D record, S-Log support and  support for ARRIRAW capability too.

Gemini 4:4:4 is a revolutionary full uncompressed HD recorder which stores video/audio data onto two removable 1.8" SSDs (Solid State Drive) for playback/transfer to a PC/MAC. Gemini supports most HD/2K formats in 4:2:2/4:4:4, 8/10-bit formats with single-link HD-SDI/3G or dual-link. A built-in 5.0" sunlight viewable (800 cd/m²), 24-bit, 800x480 color LCD touch-screen serves as a high-quality monitor and playback screen. Gemini also features an industry first: the unique ability to record to both drives simultaneously, creating identical masters.

The 680g Gemini with milled aluminum case measures 5.4 x 4.5 x 1.1" or about the same size as the popular SmallHD DP6 monitor. But, of course, Gemini also includes recording, playback, image processing, etc, etc.

This unit is idea for useres wanting to go for a higher bit rate than is currently capable with the 8 bit MPEG NanoFlash or Ki Pro mini and you can now record in 10 bit uncompressed 4:2:2 or even record with greater color sampling (4:4:4) as well as 2K/1080p50/60 support. You can also record S-log output in 4:2:2 or 4:4:4 from Sony PMW-F3 or increase the bit rate from Alexa/RED etc. 

ARRIRAW and high speed now as standard

VMI Geminis now include the 2880 x 1620 (16x9 Mode) ARRIRAW record codec now as standard. 

This shoots the full raster of the 35mm sensor on the alexa hence the frame size of 2880 x 1620 in RAW format for optimal quality and the safety area is greatly increased.  Here the image is framed with original ARRIRAW on the left and cineon quick grade for raw and log to rec 709 look into a 1920 x1080 timeline on the right.

4x3 support for Gemini 4:4:4 is now supported in both the 2880 x 1620 (16x9 Mode)and the 2880 x 2160 (4x3 Mode).

The Gemini RAW system is able to shoot at all the pre- select Alexa speeds in ARRI RAW.

  • 24fps
  • 23.97fps
  • 25fps
  • 29.97fps
  • 30fps
  • 48fps

How much Data is uncompressed?

Uncompressed is a lot of data, typically in the range of 125 to 150 MBytes/sec (1000 to 1200 Mbits/sec). But, technology advancements now make full-uncompressed workflow quite manageable and affordable. For example, using the new 10Gbps Thunderbolt technology from Apple/Intel, it is now very reasonable to edit uncompressed using a laptop. New $180, 3-TByte (TeraByte) HDDs enable portable RAID arrays with 9-12 TBytes of storage (sufficient for 18-24 hours of uncompressed 1080p24 4:2:2 10-bit).

Full uncompressed capture/editing enables the ultimate in quality with no compression artifacts, added noise, or multigenerational losses. But, you still have the option to work in CineForm/DNxHD/ProRes, etc. via a simple encode process (using programs such as Compressor or Media Encoder).

So Gemini lets you choose any CODEC you want?

Precisely! The uncompressed HD-SDI output from your camera is exactly the same data that is fed to the internal in-camera hardware CODEC. While your camera (and most recorders) only supports one CODEC, Gemini frees you to use any CODEC/format see other information tab for full details.

Dual Recording Feature for maximum security

Gemini offers two recording modes: span data across both drives, for longer record times or simultaneously record the same video to both SSDs, creating two masters (auto backup).  Two masters bring the added insurance against lost footage, while enabling some innovative work flows. For example, one SSD can go directly to the online edit station, while the second SSD can be used to generate offline proxies or H.264 footage for mobile devices / internet upload.

SSD Drive Storage

Compact Flash is a great choice for most compressed recorders, but it simply lacks the required performance for uncompressed video. Compact Flash tops out at about 90 Mbytes/sec, while uncompressed video ranges from 100 to over 300 Mbytes/sec; so clearly, it’s impossible to record uncompressed video onto a single CF card. Additionally, CF card capacity maxes out at 128GB, while SSDs are now available up to 512GB.  Note that you require 512 SSDs for high speed.

Built on cutting-edge 25nm technology, Gemini SSDs provide read/write speeds of 415/260 (Mbytes/sec) respectively. For most video formats, a single SSD has a sufficient bandwidth; however, 1080p50/60 formats generate over 300 Mbytes/sec, requiring us to strip the data across both drives. We do, however, combine the data into a single file during the offload of the SSDs to your MAC/PC.

VMI have decided that 256GB is about the maximum that anyone will want to have as a maximum storage capacity, so VMI Gemini kits are supplied with 3 x 256 SSD and 2 x 512GB SSD.

256GB SSD storage → 32 minutes @ 1080p24 4:2:2, 10-bit

Thus, you have sufficient storage of 90 minutes of 1080p with 3 x drives and more storage is available at an additional charge :

Gemini 256SSD driver storage hire: £20 per day.

Low Power Lightweight Device

Gemini follows the highly-successful design philosophy of nanoFlash to make the smallest, lightest-weight, lowest-power recorder that current technology will allow. So instead of building a PC-based recorder, which consumes 60 to 75 watts of power, we designed full-custom hardware drawing 8 to 15 Watts. Rather than designing proprietary Flash mags, we utilized off-the-shelf SSD drives, dramatically reducing both the media and transfer-station cost. (Editor’s note: The Gemini recorder package includes a 6Gbps SSD transfer station).

The Gemini is also lightweight at 680g and machined from solid aluminum billets, the case is very strong and lightweight, making Gemini ideal for extreme environments and shoulder-mount productions. The lower power enables completely silent operation (no fans) and a wide operating temperature range (projected to be -30 to +50 C).  At a volume of only 10% greater than the hand-held nanoFlash, a weight of only 1 lb, and a low-power budget, Gemini is far smaller/lighter/less power hungry than most uncompressed or compressed recorders!

S-Log Support

S-Log, maps 12-bit (or higher) linear data into a 10-bit log space (for transmission over HD-SDI, which is limited to 10-bits) and thus permits a larger range of colours to be recorded. Gemini maintains the highest possible quality, by recording 10-bit S-Log video in an uncompressed format, so there’s absolutely no added noise or artifacts.

Gemini also supports user-programmable 1D viewing LUTs, which can be selectively enabled for one or more of the SDI/HDMI outputs. Additionally, in dual record mode, you can simultaneously record the native S-Log video to one SSD (online) and the same video with burned-in LUTs to the second SSD (offline / H.264 generation).

When Gemini ships, it will include just 1 pre programmed LUT which will limit the S LOG to an extent but this will improve the record quality of the PMW-F3 enormously.

3D/Stereo option

Gemini was conceived as a dual stream recorder and will independently record two video streams to individual SSDs, for all formats except 1080p50/60. You can synchronously play-out the two individual streams or combine into side-by side, 50/50 composite or anaglyph formats. Gemini uniquely allows you to simultaneously view 3D video in multiple formats, such as side by side and 50/50 composite, which should be very helpful in 3D camera alignment.  VMI's Geminis have this option configured as standard. (Note that the 3D Option is to be released late 2011)

Gerard's Opinion

This unit has been developed as a standalone lightweight external recorder without compressed codec integration but more in an uncompressed multiple still frame-by-frame recording device in the form of a DPX file format. The idea behind it is to capture the highest amount of data acquired by a camera and is more effective in conjunction with a logarithmic compression like the Sony S-log or the ARRI log-C capturing mode seeing both dpx and logarithmic capturing requires extensive post production work which could be done simultaneously. It is similar to the old film environment of telecine with regard to a scanned negative in DPX format, then graded and taken to the non linear editing environment. The result is to increase the latitude in post in common with film and reduce the reliance for on-set grading and transcoding, so now pictures are graded in a controlled environment with proper graders and editors.

The DPX file system is a still frame-by-frame environment and transcoding is almost flawless and clients from a film background or stills time-lapse experience would be comfortable with this workflow, as opposed to converting codecs which can be time consuming and adversely affect quality.  The unit will also soon support ARRIRAW for the Alexa camera soon for the ultimate in quality.  The unit is also capable of showing a client a look up table (LUT) output, to apply a graded look during monitoring as opposed to a very unflattering logarithmic look which has a much flatter look and is the way pictures are recorded to increase the latitude.

The unit is very light and supports dual HDSDI input for 444 full colour spectrum recording and takes 2 solid state drives, which have no moving pars and thus little room for error. The drives are also much larger (256GB) than conventional card formats.  The only downside to these drives is that it they are expensive – but think of this as an insurance policy!.

The post production process, whilst fairly straight forward, can be very tricky if you don’t understand the workflow.  High end producers from a film background would find this easy but someone from a a video background must familiarise themselves with the grading process before editing.

The DPX files open natively in Adobe Premier and the higher or later AVID systems but Metafuse may be needed for older avid systems.

Apple Final Cut Users can work in one of two ways.

Firstly, as per the Film World - Grade first, where the DPX files are natively supported in Final Cut’s Color which is free but clunky and difficult to use as it is more of a colourist tool.  Then import and transcode to Final Cut Studio.

The better way is to use Glue plug in tools, so that DPX files can be directly imported to work in Final Cut Studio or Compressor, however the downside is that this is rather expensive.

The Da Vinci Resolve Lite system which is free, also works very well with DPX files but like Colour is very complicated and more of a Colourist tool.

Adobe Premier works flawlessly and offers native support to DPX, allowing you to play back on the timeline with no rendering required.  DPX files are also native in the After Effects program.

The unit has touch-screen interface which is very easy to navigate and quite responsive.  It is a powerful tool and it would need a lot of storage but delivers high data rates capturing logarithmic compression flawlessly for superb latitude. The idea of doing a LUT and future ARRI RAW on such a small machine is clearly a big help on mobile handheld, steadicam and other form of production environments where large recording devices can hinder operation and creativity.  Gerard Botha

VMI Gemini Production Kit

Gemini 4:4:4 Recorder, eSATA Transfer Station, HD-SDI cables, HDMI cable, Hotshoe with 1/4"x20
Ball Mount, Universal AC Power Supply, 4-Pin XLR Power Cable, D-Tap Power Cable, Stylus, Custom
Fitted Hard Plastic Case

3 x 256GB SSD storage
2 x 512GB SSD storage

Cased Weight

Weight  4.4kg
Dimension: 32X45X18


  • Rate: £150 per day
  • ARRI RAW/S Log External Recorder£150/day; £600/week
  • ARRI RAW/S Log External Recorder - special
    price with camera

    Special Price with ARRI Alexa or Sony PMW-F3
    with S-log.£100/day; £300/week

VMI article on HD Recorders

Best Practice Operating Guide

Selectable CODEC

The uncompressed HD-SDI output from your camera is exactly the same data that is fed to the internal in-camera hardware CODEC. While your camera (and most recorders) only supports one CODEC, Gemini frees you to use any CODEC/format.

We found that oftentimes the workflow and editing system is not well defined at the beginning of a production, or the client may want the footage in a different CODEC/format. Gemini gives you the flexibility to deliver accordingly, at the best possible quality levels. So after two weeks of shooting, when the director brings word that you’re changing from PC to MAC (or vice versa), you’re ready to encode that pristine uncompressed footage into a new CODEC / format, while maintaining the highest possible quality.

Consider also, that all professional video is ultimately transferred off the capture-media (typically Flash) onto HDDs, optical media or LTO Tape. Using high-performance multi-core processors, you can transfer and encode with little additional time penalty (compared to a simple transfer). For example, using an 8-core Mac Pro we’re getting transfer (SSD → HDD) + encode (to ProRes HQ) at 1/2 real-time. So, 30 minutes of uncompressed 1080p24 video requires a total of 15 minutes to transfer off the SSD and encode to ProRes. By comparison, a simple transfer of the same footage (without encode) occurs in 1/3 real-time, or 10 minutes.

Gemini 4:4:4™ Technical Specifications

Video Standards: HD-SDI, SMPTE 292M; HD-SDI Dual-Link, SMPTE 372M; (HD-SDI 3G, SMPTE 424M - Planned)

Video Formats 1080p23.98/24//25/29.97/30; 720p50/59.94/60; (1080p50/59.94/60, 2048x1080p23.98/24 - Planned)

Video I/O Four BNCs, (2 Input, 2 output, with individual power-down options), One HDMI (Type C) Output

Record Features Uncompressed RGB 10-Bit 4:4:4 Recording into DPX file format (audio recorded into WAV file)Spans across drives (for longer record times) or (Record simultaneously to both drives – Planned) Video can be recorded with or without baked-in LUTs

Playback Control Play and Pause (Fast-Forward, Rewind and Step – Planned)
S-Log, Log-C Support Support for S-Log, Log-C (user programmable 1D LUTs - Planned)
Media Two Slots for 1.8" Solid State Drives (SSD), 256GB / 512GB sizes;

SSD Performance: 250 MBytes/Sec Write, 415 MBytes/Sec Read, 6 Gbps SATA Interface
Note: Only SSD Media supplied by Convergent Design can be used in the Gemini

Transfer Station 1.8" SSD to 6 Gbps eSATA transfer station (included)

Built-In LCD Monitor 5" high brightness LCD, 800 cd/m², 800 x (RGB) x 480 Pixels, 24-Bit, 900:1 True Contrast,
Wide 170⁰ Viewing Angle, Color Calibrated at Factory
(1:1 Pixel Mode, with user positioning of desired window via touch-screen control – Planned)

Software Compatibility Support for Avid, Final Cut Pro, Premiere, Smoke, Flame, DaVinci

Menu System Touch Sensitive menu system with user-defined presets and customizable level of on-screen data

Timecode HD-SDI Embedded (SMPTE RP-188) or LTC via optional cable

Digital Audio I/O HD-SDI Embedded uncompressed, 24-Bit, 48K; 2-channels, stored in WAV format.

Analog Audio I/O 3.5 mm jacks, mic or consumer line level input; headphone or consumer line level output

3D - Dual Stream (Option but standard on VMI Geminis) Paid option for Full Stereo (dual stream) record and playback in a single Gemini unit;
Cameras must be Gen-locked to operate properly with the Gemini
Left and Right Video Streams recorded as individual files, in full uncompressed
Vertical Flip, Horizontal Flop, for either/both streams
Individual output of each stream or Combine: Side by Side, Line by Line, Anaglyph, 50/50 Composite
and Luma Differencing

ARRIRAW (Option) Planned support for ARRIRAW recording and playback with Confidence Monitoring

Remote Control (Option) Wired Remote Control with Tally Light and LTC I/O

Power Requirements 5 to 19 Volts DC, 8 to 16 watts (active) / 4.0 watt (power-save mode); 7-second boot-up time

Size, Weight 138 x 120 x 37 mm (5.4 x 4.7 x 1.45"); 680g (1.5 lb); Milled Aluminum Case

Environmental +40 to -10 ⁰C Ambient Temp (Operating) / +70 to -20 ⁰C (Storage)

1080p29.97/30 and 1080p50/59.94/60 data must be striped across both drives, so simultaneous
recording / 3D is not supported for these formats. (Data from two SSDs can be readily combined for

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