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Max recording bit rate? FPS? For MicroSD card purchase

Community Hero

Hi everyone,

I know that the 8 supports 4K UHD video recording, but how many frames per second does it record? Or, more accurately (because I don't know how many bits per pixel it records), does anyone know the bitrate that it records 4K UHD at?

Basically I would like to know if I can use a UHS class U1 microSD card in the 8, or if it really needs a UHS class U3 card.

Cheers :)

Community Hero

 After a bit more digging I found some answers here on the forums and on the tinterweb.

4K UHD is at 30fps, 42Mbps

1080p is at 30 fps, 20Mbps though apparently the recording is sharper than 4K

Slow motion is 720p at 120fps (I think). I couldn't find a spec for the bitrate so I did a recording to calculate it. I think it's ~126Mbps! I recorded an ~11second slow motion video and the video itself lasts ~34s and takes up 173MB. 173MB/11s * 8 (bits per byte) = 126.

I checked the file in VLC and the playback is 720p 30fps with a bitrate of ~42Mbps. So, given that the video lasts 3 times as long as I recorded it for, means the actual recording bitrate was 3x faster, therefore ~ 126Mbps is about right!

I think.

If anyone knows better and correct my logic please join in!

Cheers :)

Community Hero

 Summary: I think a UHS class U1 card will be sufficient. Probably ;)

You'll probably scrape by ok with a good quality U1 card, but the correct thing is really a V30 rated card (which will likely be U3 V30). If there's likely to be any non-media (i.e. not images, audio, video) use of it, then A1 rating may be highly beneficial. Current/latest SanDisk Extreme gives you A1 U3 V30. The SD Association added the V ratings specifically to address the performance needs of HD/UHD/4K. V30 seems to be the widely available spec at present, but there are a range of V ratings.

2 people like this
See for some useful tables and charts of the ratings.

Community Hero

Well, at first I thought I needed a U3 card, but after looking at the bitrates I didn't really understand why. The 4K UHD recording on the Nokia 8 is only 30 fps, only 42Mbps, which is ~6MB/s, therefore U1 should be fine.

What surprised me is that the slow-motion recording was a higher bit rate, ~15MB/s. For this, I should have a U3.

FYI this is what I bought:

I'll see how I get on and if I notice any problems I'll post feedback here.

Yeah, assuming your numbers and maths are correct, the basic rate should fit within U1. It does, however, omit overheads such as filesystem metadata updates (not going to be huge, but still worth remembering). As I said, you'll probably scrape by ok with a good quality card. By that, I mean there's very little margin left if the card only just meets U1 spec. V30 gets marketed as the minimum for 4K by the card vendors. While it certainly does mean more revenue for them, it's also more margin / reliability for the consumer.
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