When shooting video on a DSLR, you will be recording to one of the camera’s memory slots to a card. You’ll often feel as though you don’t have many choices when it comes to choosing your camera storage format. While some manufacturers support more than one format (offering both a CompactFlash and a Secure Digital card slot), the choice is still made by the camera manufacturer.

Card format

Knowing what each format is capable of is important. All modern storage formats have their advantages and limitations. You can use this knowledge when shopping for a new camera body or when choosing which slot to use for cameras that offer both a CompactFlash (CF) and a Secure Digital (SD) option.

CompactFlash Cards

The CompactFlash format is a mainstay for professional digital photographers.  These cards tend to be the most robust and sturdy.  The CF card format tends to be less prone to accidental damage.  It also was originally significantly faster than early SD memory cards. When comparing costs per gigabyte, CF cards are typically more expensive the SD cards. CF cards tend to be offered with faster transfer speeds than SD cards.Secure Digital CardsSD cards are most common in consumer electronic devices—in everything from music players and photo frames to GPS units. They are also increasingly becoming common in DSLR cameras.  There are three basic types of SD card in three different form factors.

Original SD – The original specification for SD cards tops out at 2 GB. Most of these cards are pretty slow.  These are probably most useful at the moment for audio recording and use in point and shoot cameras.SDHC – The SD High capacity specification allows cards to grow to 32 GB in size, and also provided for a speed increase. SDHC cards may be incompatible with older devices.

SDXC – Secure Digital Extended Capacity provides for storage up to 2 TB. It uses an entirely different filesystem on the card which makes it less compatible with older devices than SDHC.SD Form Factors – Digital video cameras typically use full size SD cards, but two other form factors are available.  The Mini and Micro sizes are used for mobile phones and other devices such as GPS recorders and some sound recorders. These small cards come in all three SD flavors outlined above.SD Compatibility – To a much larger extent than CF cards, you may find that SD cards are incompatible with some cameras and other devices. When purchasing SD cards, it’s best to research what other users of your device have had success with.  It’s also advisable to buy from a retailer that will allow the exchange or refund for a card that does not work with your camera.

Card Speed

Choosing a memory card for shooting video can be a little confusing due to the creative language used by manufacturers to make their memory cards sound fast and reliable. It’s important to remember, stills and video have very different requirements in terms of speed. Generally, for stills you need a card that is capable of keeping up with the frame buffer of the camera.A fast card allows you to shoot at high burst mode (typically a range of 3–10 frames per second) for covering fast action. For still work, using slower cards means you’ll have to wait longer for an image to appear on the camera’s LCD. It also means slower import when you transfer images from a slow card to your computer.When shooting video, using a slow card can spell disaster. The reason is that video requires a sustained throughput to the card.  The camera’s buffer is constantly being written to and then transferred to the card. If you try and use a slow card when recording video (which results in the card not being able to clear the camera’s buffer fast enough), at best you’ll drop frames and stutter.  More likely, the recording will fail and you’ll lose the shot.

Choosing a fast card is essential. But knowing what speed card to choose is not simple on first glance.

Compact Flash – rated in “x”Compact Flash is generally rated for speed using the notation 450X (or some other number).  The x in this rating refers to a speed of 150 kilobytes per second. A 10x card can transfer 1.5 megabytes in a second, etc.For video you’ll want the fastest card you can afford. This means a card that is in the 133x and above range or faster.  Try not to stay at the lower end of the spectrum as slower cards will take longer to download and transfer (with video workflows you’ll have much more date to process). Given the current market, the middle ground in terms of price and performance are 300x cards.SD – rated by “Class”It’s most common to find SD cards rated at a particular Class. These refer to the data writing speeds. A Class 2 card can write 2 Megabytes/second, and a Class 10 can write 10 MB/s.SD – rated as UHSSome SDHC and SDXC cards use the newer Ultra High Speed technology. These cards can write at a minimum of 50 MB/s. Note that to get the rated throughput, you the card and the device (camera, card reader or whatever) needs to be a UHS device, or the trans..

Source: Advice When Shooting Video to a Memory Card