Sandisk 32GB extreme (1 of 1)

I have a few Sandisk Extreme Pro SD cards laying around as well as some less “pro” Extreme cards. I spent some time today working through the math and speed testing to see if any of these cards would keep up with Panasonic Gh4’s 4k recording function. In order to save you guys some time I figured I go through it here for future reference.

Panasonic GH4k

According the spec sheet, the Panasonic Gh4 captures 4k footage at up to 200mbps which is equal to 25MB per second. If you aren’t big into tech you can find out more about bits vs Bytes here. A 64GB card, when formated, gives a little bit less than 60GB of usable space but i’m going to round to 60GB because it’s pretty close.  60GB equals 61440MB so if you are writing to the card at 25MB per second you’ll want to divide 61440MB by 25 which gives you 2457.6 seconds of recording time or about 40 minutes (40.96 to be exact) of recording time on a 64GB card at 4k.  So here’s how it works out.

200mbps data rate recording times for 4k (unknown see update) and 1080p

  • 16GB = approximately 10 minutes of record time at 4k
  • 32GB = approximately 20 minutes of record time at 4k
  • 64GB = approximately 40 minutes of record time at 4k
  • 128GB = approximately 80 minutes of record time at 4k
  • 256GB = approximately 160 minutes of record time at 4k

100mbps data rate recording times for 4k and 1080p

  • 16GB = approximately 20 minutes of record time at 4k
  • 32GB = approximately 40 minutes of record time at 4k
  • 64GB = approximately 80 minutes of record time at 4k
  • 128GB = approximately 160 minutes of record time at 4k
  • 256GB = approximately 320 minutes of record time at 4k

Sandisk extreme 32GB speed test

So will my Sandisk Extreme cards be able to handle 4k? The answer is maybe. While the Sandisk Extreme has an average write speed of 42.47MB/s in CrystalDiskMark, that’s only an average. If at any point during that test the card dropped below 25MB/s it might not be fast enough and you could end up stopping a recording. Don’t get me wrong a 42.47MB/s average is pretty good and you might be able to record 4k all day long at that speed depending on the buffer size in the Gh4, but it’s a low enough number that it could conceivably drop below 25MB/s at some point during a shoot.

Sandisk extreme pro 32GB speed test

The Sandisk Extreme Pro test tells a happier story. With an average write speed of 70.95MB/s the card would have to dip below 35% of it’s average write speed before it stopped a 4k recording. The Sandisk Extreme Pro cards are most likely fast enough to handle 4k recording on the Panasonic Gh4. This is nice when you consider that 32GB Sandisk Extreme Pro SD card are around $49, compared to the new Extreme PRO UHS-II 32GB cards at $130 a piece.

One thing to note is that Sandisk says “up to 90MB/s writes” on the Sandisk Extreme Pro cards, but they say “a minimum sustained write speed of 30MB/s” on the more expensive Extreme PRO UHS-II cards. This probably means they’ll guarantee the more expensive cards will work and leave you hanging if you have any issues with the older Sandisk Extreme Pro cards. I guess “Pro” means something different than “PRO”.

UPDATE: A few of you have mentioned that 4k recording is only in 100mbps mode. This might be the case, the answer I received from Pansonic was that “4k requires a card with a minimum sustained write speed of 30MB/s” which is actually 240mbps I assumed the extra 40mbps was a built in margin of error, but I could be wrong. Also in this interview with Panasonic at about 6:49 in the video he says 100mbps and 200mbps after talking about 4k. Maybe this only refers to 1080, but it seemed like he was implying 4k as well. If you look at the Panasonic GH4 speck sheet here at the beginning of each list is “[4K] 3840×2160:29.97p,” after the comma it lists another bit rate and format, but there isn’t any bit rate listed with the first format. Maybe this is referring to external recording formats but it’s not specified. If anyone gets a definite answer let me know and I’ll update the post again.

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