In the realm of digital cinematography, a plethora of digital storage formats is available for recording camera masters. Sony’s SxS cards, CFast cards or RED’s RED Mini Mag are just some that come to mind. Beyond those rather common choices, a seemingly endless list of obscure media formats exist for more specialized cameras or the ENG sector (electronic news gathering). But the story doesn’t end there.
After recording footage on some for of storage device, this data has to be offloaded for postproduction and archived for backup. At this stage, even more different technologies come into play. Interface formats such as USB and Thunderbolt, plus long-term storage media such as LTO systems are to be considered, too. When I first looked at this complex matrix of interconnected systems, I was baffled by this thick jungle of formats. A few questions sprung into my head.
- What are the data rates of the various devices: how quickly can you read and write data to/from them?
- Knowing the different restrictions of the devices, when used in combination, where do choke points exist: which device is most likely to slow down the process of saving, copying and finally reading data?
- What are some practical figures to be derived from this analysis?
- what considerations come into play when you want to maximize quality in camera?
- how does 4K and beyond impact the world of existing media storage formats?
- where do we go now?
Before we dive into this, a few disclaimers. First, I’m not a computer scientist: my calculations are to be taken with a grain of salt and are based mostly on theoretical figures. I have rounded values and hence incurred rounding errors. Estimates for data rates and related offload times may vary depending on your specific setup and even the sources cited often state that maximum data rates may only be reached under optimal lab situations. Furthermore, figures for device data rates vary depending on the source. I have usually taken the highest possible figure to account for the newest iterations of each technology. But now enough of this boring pretext. Let’s jump in.
For means of comparison …
I have calculated data rates in megabytes per second (MB/s, not to be confused with megabits – Mb/s) and estimated the maximum duration of storage media based on a 64GB card. If you want to know how many minutes fit your device, simply multiply this time to suit your storage size.
Wait, what are we recording?
Without going into the insanely technical discussions to be had about codecs, I have compiled a list of typical codecs used for recording camera masters. There aren’t many surprises here but it’s worth looking at the datarates of the various recording formats before evaluating the speed of storage devices later.
Apple ProRes – 12bits anyone?
Any self-respecting digital film camera should write ProRes unless recording raw. There. I said it. When shooting without color subsampling (444), ProRes records in 12bits, as opposed to its immediate rival DNxHD, which only has a maximum bit-depth of 10 bits. ProRes codecs come ready for a resolution of up to 5120 x 2160 (https://de.wikipedia.org/wiki/ProRes).
When shooting 1920x1080p25 without chroma subsampling, ProRes 4444 will clock in at about 41MB/s, which gives you approximately 26 minuets of footage on a 64GB card. For the various other variants of ProRes codecs, I’ve got a giant list of codec data compiled in my free eBook, which you can get HERE.
I recently DIT’d on a short film shot on ARRI ALEXA and we racked up 9 hours of total footage taking up 1,2 TB of storage. This was recorded onto 64GB SxS cards and we swapped cards 30 times over eight days. I will come back to these figures later.
DNxHD / DNxHR – Avid fans, rejoice.
Anyone who’s ever used Avid’s seminal Media Composer is surely familiar with this family of codecs. They are Avid’s set of digital intermediary codecs and, with slight variations, similar to ProRes. The most notable exception is the lack of a 12bit variant in DNxHD, as mentioned above.
With the advent of 4K, Avid upped the game and released a revamped set of codecs called DNxHR (high resolution – wow, naming scheme). While also able to record 4K, the HR codecs come with a 12bit option. Yay.
Shooting DNxHD’s largest variant called 440x, you will occupy space on your
device at about 55MB/s, yielding ca. 20 minutes on a 64GB device. DNxHR, when
looking at 4K, is (understandably) in a different ballpark: 186MB/s melt away
when shooting DNxHR 444 at 12bit 4096×2160 and 24 fps. This wastes 64GB in just about 6 minutes of recording time. Got a fresh card, mate? We’re full again already.
Blackmagicdesign DNG Raw
This is where I get a little wavy on the details. I’ve not shot a whole lot of
raw with Blackmagicdesign cameras so these numbers are by the book. Recording 12bit 4000×2160 pixels at 24fps you smash up 265MB/s or raw footage, filling your 64GB card in just 4 minutes. Ouch. Well, naturally, you wouldn’t be shooting on 64GB, it’s a poor comparison for raw formats. Still. A lot of data.
On my latest project, had we shot in DNG raw 4K, we’d have filled ca. 9 TB of space.
Shooting “open gate” raw on an ALEXA in 4K gives you just about the same data rate compared to BMD DNG raw. It’s 270MB/s and also about 4 minutes to 64GB. Loooots of space needed.
RED Cameras and the entire ecosystem is a bit of a mystery to me, I have to admit. I have not yet been on a RED shoot, haven’t really handled any RED footage and since can hardly say anything about the whole topic. Even doing research on the REDCODE format, it seems to be hard to put numbers to the format because, apparently, it changes with every god-damn RED camera and sensor and setting and even depends on the contents of the image. The safest assumption I can make is that shooting 8K on some carbon-fibre weaponized RED will make your producer wonder how much money one can possibly spend on hard drives. RED folks, yes, I’m being sarcastic: I’m sure REDs are great, I just never touched one, yet.
h.264 – Do we really …
No. We don’t want to talk about h.264. It makes me cry. Youtube considers 12 MegaBITS/s (!!) – that is 1,5 MB/s – a baseline for 1080p uploads. A figure I know for Canon DSLRs is about 4,5MB/s when recording h.264. That’s not a lot of data. Not at all, sir.
One thing to note, though, is this: h.264 is an incredibly smart codec that is just phenomenal at making videos small enough so that we can stream or download them in a meaningful way. It is great for web deliverables, but a very, very poor codec to be used in camera. Blocking, frame reordering and the way it destroys blacks are just a few reasons why it’s not to be used in a camera. Or editing, for that matter! But, it is very efficient. 64GB can hold about 728 minutes of Youtube-grade h.264 or ca. 242 minutes when recording on a Canon DSLR.
If you need small files for offline editing or dailies, using the respective proxy variants of ProRes (ProRes Proxy at 5,6MB/s and 195 mins per 64GB) or DNxHD 36/45 (about the same as ProRes Proxy) is highly recommended. Plus, it renders a lot quicker from your masters.
Typical Datarates of Recording Media.
Ye’ ole’ SxS (S-by-S) Card
My first foray into the domain of professional digital film cameras was, because I’m German and these cameras are f****** ubiquitous, the ARRI ALEXA, the basic, plain version with an SxS module. I’ve since been Digital Image Technician on a few shoots with said camera system and have found the SxS a practical format for a few different reasons.
- It fits into a pocket. You can easily carry four SxS cards in protective casings in your jeans or coat pocket.
- While they don’t seem indestructible, they are certainly more rugged than SD cards – gee, wow.
- They are Write-Protectable via a physical switch. I cannot stress this enough. When taking a card out of the camera, you can lock it and thus indicate it may not be used for writing on until safely processed by the person responsible.
As for the numbers, SxS cards come in many varieties but can muster up to 256GB in space while writing at up to 440MB/s. This makes SxS PRO+ cards handle even raw 4K well.
That is new SxS PRO+ cards, however. As with most of the media formats we will look at, you need to watch out what you buy, because cheaper and punishingly slow variants of these media lurk out there. And they look just the same, it’s what inside that counts. So be careful or you might get an old SxS PRO that can only handle 100MB/s and won’t do for 4K.
SxS cards are also called ExpressCard/34, which seems to be the name of the form factor. So, for example, accessories such as card readers for ExpressCard/34 are actually also SxS readers. Urgh. Much too difficult this is, young padawan.
CFast 2 – Runner Up.
In your big DSLRs, you might have seen CF cards. Watch out now, because the same thing that goes for SxS also holds true here: not everything that looks like a CFast 2 card, is one. These come with ridiculous speeds up to 600MB/s and can easily come in 256GB or 512GB. Blackmagicdesign’s URSA line of cameras comes with CFast 2 slots. For the updated ARRI ALEXA XT, you can also get CFast 2 adapters, so these nifty little cards are shaping up to be convenient allrounders.
As for the physical makeup of the cards, they strike me as a little less sturdy than SxS cards and they lack the physical lock switch, which I happen to be a fan of. Still, the CFast 2 format packs some serious speed and storage capacity, so it shouldn’t be dismissed or overlooked.
ARRI-compatible Codex CaptureDrive XR – a fancy name for an SSD
On the updated line of ARRI ALEXA XT cameras, you can outfit it with a bay for this fancy sounding solid state drive produced by Codex, a company that builds integrated solutions for on-set data management. The device looks solid and probably is, given ARRI’s fetish for rugged and battle-proof gear.
The specs also sound good: at a minimum write speed of 270MB/s it can gulp down ARRIRAW at 4K. And why wouldn’t it, seeing as it’s made for just this purpose. What I like about the format, despite never having touched it, is that it comes with an entire, integrated ecosystem of devices made solely for data management. This indicates ARRI is going their own way, just as most other camera manufacturers are doing (Sony, Red, anyone?), when it comes to storage formats.
RED MiniMag – Another Proprietary SSD
Okay, I’m going to try to be more impartial concerning Red, this time around. So the MiniMag actually looks and seems a solid (haha, pun intended) solution as a recording media for the ridiculously large formats that REDs record. It is made to fit any REDCODE format and clocks in between 225MB/s on most cameras, while achieving 300MB/s on the RED Weapon (in 8K!).
Same thing goes for this device: I’ve never touched it but it seems only natural that RED would build a fully integrated storage format fitting their cameras’ precise needs.
Sony F65 SRMASTER
To provide a comprehensive overlook for high-end cameras and their recording media, let’s quickly talk about Sony’s SRMASTER suite of formats. Basically, these are SSDs that integrate with a family of accessories and offload systems that live in the expanded universe of Sony professional cameras. The media itself sports maximum write speeds of up to 687,5MB/s (with smaller media having reduced transfer speeds).
And again, since I’ve never worked with these formats, I can’t judge the physical quality of the products but rather just report on the specs.
Note: I can’t show you images of the last three devices since there don’t seem to be any available that are public domain.
Long-term Storage: HDD, SSD, LTO
Everyone knows them. The whirring, heavy, large devices that spin up and used to make weird insect noises in the 90s. Also, you can tell when it breaks by the sound. And that just might be a feature, because if you drop them, these babies are probably f***ed.
Performance-wise HDDs aren’t that great. They come in sizes of around 4TB but speeds vary significantly. Fast drives might be in the 200MB/s ballpark, others can be punishingly slow, as in 100MB/s. Still, they are cheap and remain a mainstay of long-term file storage simply because they are easy to use and ubiquitous to the point of being a plague. Unless you specifically buy your computer with an SSD, you probably have one of these things whirring close to you as you read this.
Solid State Drives
Instead of relying on moving magnetic platters or tape, solid-state technology stores digital information in transistors that retain their charge, even when powered off. This technology is the basis of SxS, CFast and most other “card”-like storage medium today, but also comes in larger physical formats and larger capacities. These SSDs you can find in server racks as long term storage, but can also be used to distribute footage from set to post and backup facilities.
The huge advantage of these devices compared to HDDs is their higher speeds. Expensive SSDs might come in at about 600MB/s of write speed! Plus they are lighter and smaller.
Linear Tape Open
Image by Andy Hazlebury
LTO is a tape system that has been in use for many years, while constantly being updated. The current LTO 6 standard can record 6TB (yes, truly) of data and write these at about 300MB/s. Wicked.
The “thing” itself is a plastic tape cartridge with actual magnetic tape inside. I’m a 90s kid. I remember walkmans, so this makes me nostalgic. When it comes to storing large amounts of data, (relatively) quickly writing copies and distributing them, LTO is unrivaled. Take the 1,2 TB from my last project. You could write 5x this data onto a single LTO tape in roughly 1h. That’s some serious punch.
Getting from A to B
If your recording medium is A and your long-term storage is B, how do you get from A to B? Well, usually with a cable, an interface between the two media. Attach one cable to the recording device (or stick it in a reader with a cable), plug it into a computer, then run another cable to your SSD, HDD or LTO. But saying “cable” is coming up short. What types of connection interfaces are used today?
We all know USB
The universal serial bus is a magnificent connector that does many things well, even very well. Except for plugin in two orientations, that’s a pain. Besides running data from A to B, USB can also power devices such as small, portable HDDs and SSDs as well as card readers.
When using the modern USB 3.0 standard, these ports are great. They can transport data at about 400MB/s, and, if you’ve been reading diligently, you know that this is basically up to par with many other devices currently in use. Yet here comes the caveat: if you happen to chance upon a USB 2.0 device your transfer speed drops down to abysmal 60MB/s. That’s even worse than old or cheap card-media. Yikes! This actually happened to me once on a set where the university provided the computer used to offload data and it was an old Macbook without USB 3.0. We quickly ran out of SxS cards, because also, the equipment center had only provided four cards and we were shooting like crazy. The offload simply took to long for the amount of footage we were racking up. Not a good situation to be in.
Praised be the company with the bitten fruit logo. Apple’s Thunderbolt connector is simply put ridiculous. With a multi-channel throughput of 2500MB/s it is the unrivaled king of speed in this article. The connector is a little weird but it works plenty fine and is a great way to attach devices, especially card readers (since Thunderbolt HDDs are really expensive).
But there’s more
Besides USB and Thunderbolt there are such options as SCSI (which can be used to chain several HDDs to a computer), external SATA (the baseline interface for most modern HDDs and SSDs) and SDI (a connection used to send live video from cameras to recorders, monitors etc.). These, while important in their own right, don’t represent feasible options to connect storage devices to your computer for various reasons. External SATA ports are not very common and clumsy, SDI just isn’t made for this despite having the throughput and SCSI is just incredibly outdated. There, I won’t go deeper down that well. Commence the trolling.
After this exhaustive discourse on different technologies, how, now, can we use them effectively to quickly offload data from camera, copy it to long-term media and do all this without it taking forever on set? I want to look at two setups I’ve used previously that have the potential to illustrate problems, despite both being feasible setups.
SxS > Thunderbold > USB 3.0 > HDD
This is a typical setup I’ve worked a couple of times for a university in town. We record ARRI ALEXA footage onto an SxS card, plug the card into a Thunderbolt-attached reader, pipe it through the computer and back out to two USB 3.0 hard drives.
If we now list the speeds of the components of this chain, we immediately identify a problem.
100MB/s > 2500MB/s > 400MB/s > 100MB/s
The fastest segment in the chain is the Thunderbolt connector between the SxS card reader and the computer. The USB 3.0 connection to the hard drive is also faster than both the SxS card or the HDD in use. With this setup, using MD5-verification after the copying is done, an offload of 64GB takes ca. 20 minutes. It could be at least four times faster if a new SxS PRO+ card and an SSD or LTO drive were used.
In practical application, while it clearly is not optimal, it is not a major problem. Given the shoot progresses slowly and you have enough SxS cards to cycle through the camera, you won’t be waiting on the offload to free up a card for recording. However, if you do end up with three full cards in your pocket at the end of the day, you will be waiting for 1h plus for the offload, probably long after every other department has gone home. Also, this setup doesn’t permit 4K recording and might not be able to sustain 100fps.
CFast 2 > USB 3.0 > USB 3.0 > SSD
Here, we simply swapped out a few components in the daisy chain and see what it got us. Instead of shooting on an old SxS, we update to CFast 2. Also, instead of writing to an old HDD, we plug an SSD into out computer. And since we might not always be using Apple Macs, we are also using USB 3.0 to connect both the CFast 2 card reader and the SSD.
Let’s look at the respective speeds of the devices.
600MB/s > 400MB/s > 400MB/s > 600MB/s
This looks a lot more homogenous. With this setup, the USB 3.0 connection is actually throttling down the transfer, but things are, overall, still proceeding much more quickly. At this rate, your 64GB CFast 2 would be offloaded (including MD5 hash verification) in maybe 5 or 6 minutes. Now that’s what I’m talking about.
For the daily application of these figures on set, when you are working with camera data, I will have to make a few assumptions based on my (limited) experience on larger sets.
- Shooting Ratio. This is a general term for the amount of footage captured compared to the final length of the film. On digital productions, this can easily be 20:1.
- Minutes per Day. You might be shooting anywhere from 1 minute to maybe 5-6 minutes of the final film per day, depending on how long your shots are (masters or coverage) and the type of scene (dialogue or action). Let’s stick with 2 minutes a day.
Therefore, if you are shooting 20:1 and 2 minutes of final film a day, you have the camera running for 40 minutes per day. Let’s assume you’re not shooting raw. You’re recording 1920x1080p25 in ProRes 4444 (41,25 MB/s). Then you’re filling 41,25 x 60 x 40 = 96 GB per day.
96GB will offload depending on the lowest transfer speed in the following time:
– case one: limited to 100MB/s at the slowest junction, offload will take about 32 minutes.
– case two: with increased transfer speed of about 400MB/s we reach 8 minutes to offload the entire day’s worth of footage.
That sounds reasonable.
Take into consideration …
- 4K and beyond. The sheer size of our frames is expanding and the data rates grow just the same.
- Framerate. If you want to go for higher framerates, you will incur drastic increases in required bandwidth. Around 50MB/s for 25fps is fine on slow devices, but what if you want to go 250fps? Can your device measure up? Do you maybe have a burst mode and on-camera buffer like the Sony FS700? You will want to think about these things.
- Price. If you own rather than rent your gear, price is a significant factor determining what you can record, and what your daily workflow might look like. Maybe you’re a one-man show and only offload your giant card at night without any stress. Maybe you want to cycle media through on a roster and need lots of smaller cards. These decisions will impact your budgetary requirements.
- Off-camera recording. I have not talked about recording on external recorders and what recording media these things use, because it seems that is an entirely new and special world of its own.
Limitations based on Computers
Whatever the transfer speeds of your various media, cables and so forth, speedy transfers can still be impeded by limitations in your computer hardware. Fast RAM (random access memory), a quick processor and large bus on your mainboard might further hinder fast transfers. Basically, using a shitty computer to handle data will also slow down your workflow.
And the verdict is …
Whatever ridiculously large camera master format you want to record, there are media formats and transfer methods available that will make it possible in a sensible way. That is good to know but also, once you think about it, not really surprising. After all, the manufacturers that construct 4K and larger cameras want to make sure the data they can record is actually usable. So they put systems in place that facilitate these workflows. Most notably, all of the major players in the digital cinema camera market (sorry, Blackmagicdesign, not counting you in just yet) have devised storage solutions that are tightly integrated with their cameras. These systems essentially prescribe a complete workflow to ensure no data is lost.
On that note, one cool tip I actually learned in uni: Never carry all copies of a production at once 🙂 Really, this should never happen but, low budgets don’t always spend big on storage. Always keep one separate copy off-site from where ever you might be. Never have all backups in one place at once!
Hopefully, this lengthy article provides both an overview as well as given you a piece of reference for baseline figures regarding the most common storage solutions. That is really why I wrote this, to learn for myself what is out there and what you need to get to have a smashin’ fast workflow. So no, I’m not sorry this is long and number-focussed behemoth.
Also published on Medium.