Terms such as read speeds, write speeds, UHS Speed Classes, CF, XQD, SD, V Class and many more may seem like techno babble to many, but they are key to choosing and using memory cards to capture and manage your video footage. In this guide we’ll delve into the sometimes confusing world of memory cards and explain what you need to know when choosing memory cards for shooting video.
What you’ll learn
- Memory card formats & slots explained
- The importance of read and write speeds
- The Speed classes of cards
- Top tips for choosing memory cards
- The choices for external storage systems
With an ever-increasing range of cameras – from affordable compacts, mirrorless models and budget DSLRs through to professional digital cinema cameras – now offering video shooting at 1080p Full HD, 4K resolutions and upwards the choice of which memory cards to use is more crucial than ever.
Unsurprisingly, shooting video eats up much more memory than shooting stills… so which cards you choose to use is key. To give you some guidance in this blog we’ll examine the different types of memory cards, what the classes of memory card mean, their speeds and top tips for what you should consider when buying memory cards for shooting video…
Memory card formats & slots explained
Whilst there have been many variants of card types and formats the two most common card formats have been Secure Digital (SD) and CompactFlash (CF) cards. SD cards are used in all types of cameras – from point-and-shoots to professional digital cinema cameras – with the smaller microSD cards now often utilised in cameras such as HD camcorders and aerial cameras. CF cards are more robust and durable and are often used in pro-spec DSLRs and digital cinema cameras.
Many cameras that record digital video offer dual memory card slots. For example, the Canon EOS 5D Mark IV DSLR includes one SD card slot and one CF card slot, whilst the Panasonic GH5S camera features two SD card slots.
The benefits of dual card slots are that once one card is full of data you can continue to record on the other one and, of course, you will be safe in the knowledge that you have not missed any shots. Do, however, get to know exactly how your dual card slots work in tandem so you can set up your camera to maximise how they work together.
Understanding memory card read/write speeds & Class ratings
The speed of a memory card pertains to both its read speed and its write speed. Write speeds describe how quickly images or video can be saved to a card. The read speed denotes how fast data can be retrieved from a card – for example, when transferring your video footage to a computer or hard drive.
Generally read speed is always faster than write speed but write speed is absolutely essential for video as you will need your cards to have both the speed and the capacity to deal with recording large amounts of digital video data.
The speed of a card is shown with either a multiplication value – each ‘x’ value represents .15MB/sec, so 2000x multiplied by 0.15MB/sec denotes 300MB/sec – or the more recent ‘Class’ rating.
The speed Class rating was based on requests from movie and video companies, as video recording in different formats and resolutions requires certain write speeds when recording to a card.
The Class ratings denote the minimum write performance to record video – a Class 2 card can handle sustained writing of data at 2MB/sec, a Class 4 card will handle 4MB/sec, Class 6 at 6MB/sec and Class 10 is the fastest at 10MB/sec. As a general rule of thumb you’ll need at least a Class 4 card to record Full HD video but it’s probably best to go for Class 10 for most uses.
To cater for the large amounts of data required for shooting 4K, 360 degrees and 8K video there is now a V Class rating, which was created by the SD Association. The highest V rating is V90, which denotes a minimum sustained speed of 90MB/sec. The other V Class ratings are V60, V30, V10 and V6, in which the numbers denote the MB/sec speed.
On test benches cards can achieve faster speeds but it’s better to work off the ‘sustainable speed’ rather than the ‘achievable speed’. It’s a bit like cars that claim 60mpg performance under test conditions when the reality is probably closer to 40mpg. As a rule of thumb if you’re shooting 4K RAW you’ll need write speeds of at least 75MB/sec for it to keep up without dropping frames.
UHS Speed Classes explained
The so-called UHS Speed Classes indicate how quickly video content can be transferred to a memory card. UHS-I enables maximum transfer speeds of 104MB/sec, while UHS-II enables speeds of up to 312MB/sec.
Within the UHS Speed Class there are two designations, U1 and U3, which represent minimum write speeds of 10MB/sec and 30MB/sec respectively. For video shoots it’s usually best to choose a U3 designated card as this will cope with 4K video.
CFast, XQD & CFexpress
As you’ve no doubt gathered, speed is of the essence for shooting video and CFast 2.0 cards were once the leaders in terms of speed. The original CFast 2.0 card, launched in 2013, promised read speeds of 450MB/sec and write speeds of up to 350MB/sec.
CFast and XQD cards were created by the CompactFlash Association (CFA) to replace the CF card format as it had reached its maximum performance capabilities. In their current versions CFast cards have a theoretical limit of 600MB/sec and XQD cards 1000MB/sec. They are ideal for shooting 4K video resolutions and beyond.
The next generation of high speed, removable storage is CFexpress, which merges the CFast 2.0 and XQD 2.0 standards. The only drawback for CFexpress cards is that, as yet, they are not compatible with many cameras but this is likely to change in future.
Card capacity
Every memory card will have its capacity shown on it – for example, from 4GB up to 512GB. The capacity values always double, so cards will have capacities of 4GB, 8GB, 16GB, 32GB, 64GB and so on. Naturally enough, the larger the value the more capacity a card has to store images and/or video.
Which memory cards to buy for video?
The choice of memory cards can be baffling. For example, within the SD card variants the so-called SDXC (Secure Digital ‘Xtra Capacity’) cards have much higher capacities and processing speeds than the original SD cards, but you have to make sure your card choice works with your camera.
For more on this, check out our guide to the best memory cards for video.
Know what your camera supports
It may seem obvious but you should be aware of the fastest card speed that your camera supports. Check the instruction manual or manufacturer’s website to ensure that your preferred card matches what the camera is capable of.
How to pick the write speed you need
For write speeds memory card maker SanDisk recommends Class 2 cards for standard video, Class 4 for HD Video, Class 6 and upwards for Full HD video, UHS U1 for Full HD video supporting real time video recording and U3 for Full HD and 4K Video supporting real time video recording. Consider what resolution of video you will be shooting and choose the Class accordingly.
Go above your maximum capacity
Ask yourself how long you plan to shoot for and how many cards you’ll need to do so? You can quite quickly make simple mathematical calculations based on the amount of time you plan to shoot for and the resolution you’ll be shooting at.
Make sure you have enough storage capacity to cover your shoot. You never want to be caught short of storage when shooting, so always bring at least one extra card over and above your estimated pre-shoot capacity!
Play it safe
You may be lucky and have found a budget card that works well for your workflow but, in general, it’s safer to stick to high-capacity cards from well-known brands such as SanDisk, Sony and Kingston.
They are usually faster, more reliable, more robust and will provide more back-up measures for your work. In all cases make sure you have done your homework before buying your cards. For example, Nikon’s DSLRs use the XQD card format.
Get the best card reader
Buying the fastest memory card available won’t do you much good if you have a slow reader. For example, if your computer has a USB 3.0 port, buy a good USB 3.0 reader to take advantage of fast read speeds. This can save you significant time when transferring your images or footage and will mean you can start working on your edits much sooner.
Storage solutions
As well as your memory card choices you’ll also need to make decisions as to how to store your video footage before editing. For most amateur videographers a high capacity portable hard drive will suffice although you also have the choice of using a RAID set-up (an array of hard drives for larger capacity) or a server based storage set-up.
Again, do your homework before making a final choice and make sure that what you choose to use for storage is best for your capacity and compatible with your interface.
The four factors for choosing a memory card
If all of the above seems like a lot of information to take onboard it’s worth just remembering four key factors for memory cards – card type, speed, capacity and price. In terms of shooting quality video it’s not really worth compromising on any of these criteria. For example, a lower priced card will often have the pay off that it will offer lower speeds.
Whilst some online memory card offers may appear very tempting, it’s best to buy via an established photo/video dealer or a large electronics chain. After all, there’s no point in taking any chances when capturing and transferring your precious video footage.