Blackmagic Forum

Hi
As many others here I'm waiting my BMPCC 4K to ship.

I have asked BM support about certified media to handle 4K DCI @60fps RAW, but they could not give me any information, and they have not yet published certified media list for this camera.
I need that for a specific project where each frames is treated as a still, and need the best possible quality.

I would like then to discuss which media can support 4K DCI @60fps dng.
Official BMPCC 4K specs on BM website says 272 MB/s @30fps.
That means 544 MB/s @60fps.

As stated here by Kristian Lam:
viewtopic.php?f=2&t=72674&p=413154&hilit=bottleneck#p413154
BMPCC USB-C port "It will be USB 3.1 Gen 1 (5 Gbps)."
If it is 5 Gbps, it's in reality is USB 3.0 Gen 1, not 3.1 Gen 1 ?

Now concerning USB 3 gen 1:
https://en.wikipedia.org/wiki/USB#USB_3.x
"At a 5 Gbit/s (625 Mbyte/s) signaling rate with 8b/10b encoding, the raw throughput is 500 Mbyte/s. When flow control, packet framing and protocol overhead are considered, it is realistic for 400 Mbyte/s (3.2 Gbit/s) or more to be delivered to an application"

So clearly, my doubt is: how can BMPCC 4K record 544 MB/s on a SSD if USB port bottleneck at 400 MB/s?
I've been hoping to use a M.2 MVMe fast SSD in an MVMe USB-C enclosure, but my hope have vanished.

I would be glad to have this community other members opinion.

Thanks

Jean-David

Your only choice to record 60fps raw is to use 3:1 compression or braw later when it will be released in a firmware update for the PCC4K.
If you really absolutely need lossless compressed raw, then unfortunately this camera is the wrong choice for you and you are better of with an UMP or UM46K with two CFast slots to be written to simultaneously.

Perhaps BMD will be able to support writing to a CFast card and an SSD over USB-C simultaneously in a future Firmware update for the PCC4K, but I went count on that any time soon or ever.

You could contact support and file in a feature request, they are listening and if requested enough and possible to implement it will get onto the list of features to do.

Thanks Robert for those hints, in particular to request the feature of simultaneous writing to CFast and SSD...
Where is the right place to make a feature request? Just this forum or any BM specific page? Couldn't find that...

You can find the contacts in the support page down below or just follow this link and wait for the webform to pop up:
https://www.blackmagicdesign.com/support/contact/email

Thanks again.
Now how is working the cdng 3:1 compression ?
Loss of chrominance? Up to which point is it visible on a single frame?

Due to the limitations of USB 3.1 gen 1 aka USB 3.0, as you are aware, Wise has advised that their Portable SSD will record DCI 4K 60p CinemaDNG raw 3:1. Their device is expected to be released mid-October. That may be satisfactory for your purposes as each frame is a still image.

All BMD raw is 12bit colour and maintaining the correct colour across the raw codecs is a high priority of BMD.


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Thanks Rick for clarifying.
CinemaDNG RAW 3:1 is 129 MB/s @30fps, so 258 MB/s should be the bitrate @60fps.
So this would fall in the range of a common Samsung T5 writing speed.

About Wise SDD, thanks, I didn't know, I found this:
https://www.newsshooter.com/2018/09/01/ ... irtv-2018/
"Wise told us that the SSD has been optimised for 4K RAW recording at up to 60fps".
What does that mean?
What would be the benefit of using the Wise over the Samsung?

I own a Samsung T5, as soon as I receive my BMPCC 4K, I'll make some tests and report.

Jean-David

With any connection and storage you'll have to calculate for some overhead.

The guy from wolfcrow made a test with the T5 (check on YT): doesnt work!

While it is actually pretty bolt from BMD to not state that, I can imagine no scenario where you would want to shoot uncompressed RAW...so I can live with it...

Well wolfcrow video is not so clear

@25:55 he writes he gets about 260-300 MB/s for lossless raw 4K @60fps !!!
Later he says it's OK with the T5.

Anyway T5 is also advertised at about ~540 MB/s.
At this point, Wise SSD is said to be better optimized for this, but there is no proof it's more than marketing...

It looks like Wise has had access to a BMPCC4K for their testing. As I’ve reported in other posts, the Wise Portable SSD is doing raw 3:1 DCI 4K60p due to the limits of the SATA interface. The drive is USB 3.1 gen 2 (10Gbps). It the camera is limited to USB 3.1 gen 1 (5Gbps) and actual transfer rates are going to be less expensive than theoretical maxima.


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The up to 540 or 525 ratings don’t mean anything when you’re recording video which requires a sustained data rate, not a two second file copy. And often those rates assume the data has not been compressed so their actual rates with video (always compressed already for the latest BMD cameras and codecs) so you really get much less data rates than those maxima once again. Wait for BMD to post their test results.


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domisol wrote:Well wolfcrow video is not so clear

@25:55 he writes he gets about 260-300 MB/s for lossless raw 4K @60fps !!!
Later he says it's OK with the T5.

Anyway T5 is also advertised at about ~540 MB/s.
At this point, Wise SSD is said to be better optimized for this, but there is no proof it's more than marketing...

Thats the one I meant...he made just a video for testing cards: