Sunday, 18 May 2014

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
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.

9 comments:

  1. The SD Speed Class ratings are worst-case performance - meaning the card must be able to write at that speed even if the card is heavily fragmented and almost full and used in a device that barely supports the same Speed Class rating.
    If you are using the card more carefully (not deleting pictures or video in camera, and reformatting in camera immediately after copying files onto the computer), you will get closer to the manufacturer's rated speed.
    If you need to be absolutely sure you can capture the video you want under all circumstances with multiple people using the camera, possibly multiple cameras sharing the card, possible deletions in camera, and filling up the card often, go with the SD Speed Class rating.

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  2. Sandisk Extreme 45MB/s works for me in all cases.

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    Replies
    1. Yes, that has been my experience as well.

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  3. FYI,
    I tried recording 4K 30p on a 64GB Sandisk Ultra SDXC Class 6 30MB/s and I got that message after 10s, @4K 24p it did handle a few more seconds, but nothing that I would rely on.

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    Replies
    1. Yes, I agree. I would go for a 45MB/s card for 4k video, which is what I recommended in the article.

      It seems that the recent Lumix GH4 firmware upgrade increased the average bitrate a bit.

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    2. Hej Frederik, first of all thank you very much for this very valuable blog!

      I've noticed the same thing: while GH4 firmware V1.1 gives me roughly 80 Mbps in the video stream of the 4K 100 Mbps format, V2.x have increased to around 100 Mbps. A similar thing goes for the FHD 200 Mbps setting, where firmware V1.1 gives me around 150 Mbps bitrate in the video stream vs 200 Mbps in the V2.x firmware. I'm using Sandisk Extreme 45 MB/s cards and can confirm that so far, I've not encountered any problems with the cards, no matter the bitrate setting.

      However, on my computer I find both VLC and my NLE to take a significant performance hit (in terms of FPS) during the higher bitrate 4K video playback - both when the video is played back from internal SSD or even RAM, to the extent that I've decided to stick to the lower bitrate V1.1 firmware for now.

      Just wanted to share this information, because I found Panasonic's statement in their announcement of GH4 firmware V2.1, "Playback performance of recorded 4K video is improved.", not to be true in my case. As they say, your mileage may vary...

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    3. Thanks for your detailed information! I have not measured the bitrate before/after the firmware upgrade, but it is interesting to see that the difference is so big.

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  4. Hello everyone,

    I just got a new 64GB Transcend SDXC card (viz photo) for shooting video in my Lumix GH4. I shoot .mov and when I shoot on all different modes (1080 / 1080 96fps / 4K ) it shoots no problem.

    But when I copy the video to my Mac and I play the original (H 264 mov) files from the camera, the video is lagging very very much. That is not an issue when I play the video in the camera in Playback mode. Nor seems to be an issue when I convert the .mov files to an Apple Pro Res codec (for editing) and play them again - they are not lagging.

    Does anyone else have this issue? Am I STILL using a slow / wrong SD Card? Am I doing something wrong? I want to make sure I am not loosing any footage/quality in my videos.

    Thank You!!

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    Replies
    1. It sounds like the problem is your computer. It appears to not be able to playback the video from the original file container (H264). As you are able to use the files for video editing, this doesn't sound like a big problem.

      Just don't playback the original files, but use them when editing videos and encode the outcome in a format that your computer can handle.

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