Do you need new SD cards for GH4?

Recently, there has been a lot of talk about the Lumix GH4, and that you need the new, very expensive, UHS Speed Class 3 (U3) cards to use the 4K feature. Well, do you?

My answer is: You probably don't need any new SD cards. Keep reading to see why.

Card speed ratings

When you buy an SD card, you pay for three things: The brand name, the capacity (size), and the speed. The branding is in fact quite important for the price, which is the reason why counterfeited cards is a big problem. You can read about my experience with counterfeited SD cards here.



Here are some Sandisk cards I had lying around. They are ordered from the slowest (20MB/s) to the fastest (95MB/s):

From left to right: Sandisk Ultra 20MB/s, Sandisk Ultra 30MB/s, Sandisk Extreme 45MB/s, and Sandisk Extreme Pro 95MB/s

The highest bitrate video the Lumix GH4 can produce is in 1080p ALL-Internal, 200Mb/s. This corresponds to 25MB/s (eight bits per byte), so one might think that the three fastest cards above can handle this.

However, it is not that simple. The rated speed is the maximum. A card rated at 45MB/s typically has an average write speed of around 30MB/s. So the only way to be sure, is to test the cards.

Test

At first, the results surprised me. I was able to record 200Mb/s footage on all the cards. However, I quickly found that not all cards could sustain writing for more than about 10 seconds. This is probably because the camera buffer only covers some seconds of footage. But the good news is: Even with a slow card, you can record short video clips in the highest bitrate.

Here is a test of which cards were able to record video footage for a sustained period:

Card speed	Sandisk Ultra 20MB/s	Sandisk Ultra 30MB/s	Sandisk Extreme 45MB/s	Sandisk Extreme Pro 95MB/s
1080p All-I 200Mbps	No	No	Yes	Yes
4k 100Mbps	No	Yes	Yes	Yes
1080p 100Mbps	No	Yes	Yes	Yes

As you see, I was able to record 4K on even one of the slower, cheaper cards. To be on the safe side, though, I would go for at least a 45MB/s rated card.

If you are going to be using the highest bitrate 1080p ALL-Internal 200Mb/s mode, then you might want to invest in a 95MB/s rated card. But I was able to use a cheaper 45MB/s rated card as well.

But do you really want to use this mode? I think the ALL-Internal mode is only interesting if you specifically need a high consistency between each frame, for example for blue screen use. But this mode compresses the footage less effectively than the 100Mb/s, since it does not do any compression between the frames. For most normal use, you would be better off using the 100Mb/s bitrate mode, and you save a lot of disk space as well.

Conclusion

So do you need a new SD card for the GH4? It depends on what card you have already, of course. But in my experience, an expensive UHS Speed Class 3 (U3) card is not needed. If you already have a high end SD card, you can probably use that for your 4K videos with the Lumix GH4.