The wrong card drops frames mid-take. Here is how to match SD or CFexpress to your camera's bitrate, and which cards actually sustain the write speeds they claim.
A memory card seems like the boring part of a kit until your camera stops recording mid-take because the card cannot keep up. For video, the number that matters is not the big read speed on the label, it is sustained write speed: the minimum the card can dump data continuously, take after take, without faltering. High-bitrate, 4K 10-bit, 6K and 8K RAW codecs demand serious, consistent writes, and a card that bursts fast but sags under sustained load will drop frames or throw a buffer error. This guide explains the formats (UHS-II SD with V-ratings, CFexpress Type A and Type B), how to read speed-class symbols, and how to match a real card to your camera's bitrate so recording never stops when it matters.
Card labels scream read speed (how fast you offload footage) and a peak write speed, but video recording cares about minimum sustained write: the floor the card guarantees while writing continuously. A high-bitrate codec writing 400 Mbps needs a card whose sustained write comfortably exceeds that, with headroom for safety.
Convert your codec's bitrate from megabits to megabytes (divide by 8): 400 Mbps is 50 MB/s. That looks easy, but RAW and high-frame-rate modes can demand 1,000 to 2,000+ Mbps (125 to 250+ MB/s) sustained, which is where SD runs out of room and CFexpress takes over.
On SD cards, the V-rating (Video Speed Class) tells you guaranteed minimum sustained write: V30 = 30 MB/s, V60 = 60 MB/s, V90 = 90 MB/s. For demanding 4K and lighter 6K, you want UHS-II with a V90 rating, which sustains 90 MB/s and reads up to about 300 MB/s.
UHS-II cards have a second row of pins on the back; a UHS-II card in a UHS-I-only slot still works but at slower UHS-I speeds. If your camera is SD-only, V90 UHS-II is the best you can do, and it handles most 4K 10-bit and ALL-I modes comfortably. Proven V90 lines include SanDisk Extreme Pro, ProGrade, Angelbird AV Pro, Lexar Professional 2000x, Kingston Canvas React Plus and OWC Atlas Ultra.
CFexpress is now the format of choice for high-end cameras because it is dramatically faster than even UHS-II SD. There are two physical sizes that are not interchangeable: Type B is larger and faster, used by Canon, Nikon, Panasonic and others; Type A is smaller and Sony-specific, used in Alpha and FX bodies that often also accept SD in the same slot.
Type A tops out lower than Type B (around 700-900 MB/s on 2.0, up to ~1,800 MB/s read on 4.0) but is plenty for Sony's high-bitrate and RAW modes. Type B 2.0 reaches ~1,700 MB/s and the new 4.0 generation pushes past 3,000-3,700 MB/s read with 2,000+ MB/s sustained write, which is what 8K and 6K RAW need. Crucially, a Type A card will not fit a Type B slot and vice versa, so buy for your exact camera.
If your camera only has SD slots, the decision is made: get V90 UHS-II. If it has CFexpress, use it for any high-frame-rate, ALL-Intra, ProRes or RAW mode where SD would choke. Many hybrid bodies have one CFexpress and one SD slot, letting you record proxies or backups to SD while the heavy codec hits CFexpress.
CFexpress 4.0 is backward compatible with 4.0-capable cameras and offloads footage far faster, but in an older 2.0-only camera a 4.0 card runs at 2.0 speeds. Match the generation to your body and your patience for offloading. For 8K RAW, CFexpress is necessary, not optional.
Sustained-speed leaders for video include ProGrade Cobalt and Sony TOUGH on Type B, which hold among the highest minimum write rates available. Cards with VPG (Video Performance Guarantee) certification, like VPG400, promise a guaranteed sustained floor, which is exactly the assurance video needs.
Buy genuine cards from reputable sellers (counterfeits are rampant), get a matching high-speed reader so your card is not bottlenecked at offload, and format cards in-camera before each shoot. Note that prices on CFexpress shifted in 2026 with several brand increases, so check current retail before buying.
A proven, affordable V90 UHS-II card that delivers consistent sustained writes for hybrid shooters who need both stills bursts and 4K video. A safe, well-priced default for SD-slot cameras.
Best for: Hybrid creators on SD-only mirrorless bodies
The benchmark V90 SD card, with up to 300 MB/s read and 260 MB/s write and a long track record of reliability. Handles 4K 10-bit and ALL-I codecs without dropping frames.
Best for: 4K shooters wanting the most trusted SD card available
A favorite among video pros for rock-solid sustained writes and durable build, designed specifically for sustained recording rather than burst stills. Reassuringly consistent on long takes.
Best for: Documentary and event shooters who record long, continuous takes
The reliable Type A choice for Sony Alpha and FX bodies, with high sustained writes that unlock S&Q high-frame-rate and high-bitrate modes SD cannot sustain. Rugged TOUGH construction resists bending and water.
Best for: Sony Alpha and FX shooters needing high-bitrate and S&Q modes
A dependable Type B workhorse for Canon, Nikon and Panasonic bodies, with fast, consistent writes that handle 8K, 6K and 4K RAW recording. The default safe pick for high-end mirrorless cinema.
Best for: Canon, Nikon and Panasonic cinema shooters recording RAW or 8K
Optimized for video with a minimum sustained write around 1,400 MB/s, among the best sustained rates in CFexpress 2.0. Built for continuous high-bitrate recording where dropped frames are unacceptable.
Best for: Pros who prioritize guaranteed sustained write over peak burst
A next-gen 4.0 card hitting up to ~3,530 MB/s read and ~3,200 MB/s write with a sustained floor over 2,000 MB/s, built for 8K, 6K and 4K RAW. Reads stupendously fast for near-instant offloads on 4.0 readers.
Best for: 8K and high-bitrate RAW shooters on 4.0-capable cameras
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Check the manual or the slot label. Type A and Type B CFexpress are physically different sizes and not interchangeable: Type A is Sony-only and often shares a dual SD/Type A slot, while Type B is used by Canon, Nikon and Panasonic. SD-only cameras need UHS-II V90 cards.
V90 is a Video Speed Class guaranteeing at least 90 MB/s sustained write on an SD card. For 4K 10-bit, ALL-Intra and lighter 6K on an SD-slot camera, V90 UHS-II is what you want. Lower 8-bit 4K can survive on V60, but V90 buys safety headroom.
Only if your camera supports it. CFexpress 4.0 roughly doubles speed (3,000+ MB/s read) and offloads footage much faster, but in a 2.0-only body it runs at 2.0 speeds. For 8K RAW and the fastest offloads on supported cameras, 4.0 is excellent; otherwise a good 2.0 card is plenty.
Almost always because the card's sustained write speed cannot keep up with your codec's bitrate, even if the peak read number is high. Match the card's minimum sustained write to your highest bitrate with margin, and confirm the card is genuine and formatted in-camera.
Size by codec bitrate and shoot length. A rough rule: minutes of footage equals capacity in MB divided by bitrate in MB/s. High-bitrate 4K eats roughly 3 to 6 GB per minute, and RAW far more, so 256GB to 512GB is sensible for full-day shoots. Carry multiple smaller cards to limit risk if one fails.
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