Blackmagic Forum

Hi,

I got a brand new BMCC 6K a couple of weeks ago.
My recording media is a brand new Sandisk Extreme Pro Portable SSD V2 (SDSSDE81-2T00), which is on the recommended drives list, and I'm using a Tilta USB-C cable (also brand new) that screws onto the Tilta cage and SSD-holder I got.
I have the battery pro grip, with new NP-F batteries, so 3 new batteries in total.

Using the Blackmagic Disk Speed Test utility with the cable and SSD, I got read and write speeds of 900+ MBps.

So cable and drive should be fine, yet I'm getting dropped frames after about 40 minutes into a live show.
I used the BMCC as a wide angle to record the entire show and it wasn't being operated at all during recording, so there's no difference between the first half hour without dropped frames and the moment frames start dropping.

I'm shooting Open Gate at 25fps on Constant Bitrate 3:1, which normally shouldn't be a problem since I'm getting 900+ MBps on the disk and cable.

Any ideas on what this could be?

Thanks in advance for your help!

Kind regards,

Bram

Support pages says:

The following USB-C dives are recommended for recording 6K (Open Gate) Blackmagic RAW 5:1 up to 36 fps and 6K DCI Blackmagic RAW 5:1 up to 48 fps.

In theory (and what I read from dedicated tests) the drive itself should perform well without dropping frames. But a camera is not a PC and the SSD itself can draw between 3.6 up to 7.3W on the USB-C port.
The faster it writes, the more it draws, maybe that is the reason BMD recommends it up to 5:1.
After 40 min dropping frames could mean the first battery was nearly depleted (but not switched over the the next one) and could not provide enough power - the drive runs into a problem with that and then is dropping frames...
You could do a recording test with the camera on a power supply.

Otherwise I'd always recommend using an internal CFexpress media over external media.

I have had perfect results on the P4k using this media. I think it's worth consideration.

https://www.bhphotovideo.com/c/product/ ... _525r.html

I understand wanting to use a USB drive because it's so cost effective but the prices on CFExpress and pretty damn good and they're way faster than USB 3.1 Gen 1. I found their sweet spot, price wise, is 1TB and 2TB ones will be expensive but you can make your own for cheaper by buying a 2230 m.2 drive and placing it in an m.2 to CFe enclosure. Just make sure you pick something that has decently low power usage.

Jim Simon wrote:I have had perfect results on the P4k using this media. I think it's worth consideration.

https://www.bhphotovideo.com/c/product/ ... _525r.html

BMCC 6K doesn't use CFast cards, it uses CFExpress. Bram is currently using a 2TB drive so 256GB is waaay lower. He's shooting open gate 6K, not 4K so the data rates are going to be much higher.

If 1TB is enough for his needs, this Angelbird 1TB AV PRO SE should do the job though.

https://www.bhphotovideo.com/c/product/ ... press.html

Hey everyone,

Thanks a lot for the help already!

I did some more testing with the power adapter attached and I'm still getting dropped frames at 3:1.
This is on USB-C, but at least I can rule out the batteries as the source of the dropped frames.

I tried it at 5:1 with the power adapter and got the same problem.
This time the drive became really hot though, so it could've been an overheating problem with the ssd.
Which surprises me, because it should be able to handle some heat. Could that be a manufacturing defect?

Switching to CFExpress is a much more expensive endeavour in Europe, prices are waaaaayyy higher because most cards need to be imported. So if I don't have to switch from USB-C, I'd rather not.
An Angelbird AV PRO SE 1TB is about €350, I found one with a big discount at €250, but that's still a long way from €210 for 2TB.

BramSmans wrote:Switching to CFExpress is a much more expensive endeavour in Europe, prices are waaaaayyy higher because most cards need to be imported. So if I don't have to switch from USB-C, I'd rather not.
An Angelbird AV PRO SE 1TB is about €350, I found one with a big discount at €250, but that's still a long way from €210 for 2TB.

Huh? Angelbird is an Austrian manufacturer.
And US prices are always excluding VAT, while EU prices have to include VAT. If you are a professional with a VAT number you can buy in the EU outside of your own country VAT free.

And just to remind you how cheap CFExpress has become compared to when we started with CFast:

In 2016 when I bought cards for the URSA Mini 4.6k - a Lexar 256 GB CFast2.0 card did cost 600 Euros - and people complained how expensive that was compared to an 2.5" SSD like you could use in the first BMCC 2.5k camera.
In 2019 I bought 2 of the very first 1 TB CFast2.0 cards from Angelbird - each at 1.800 Euros including VAT. That did hurt.

Try this special offer, maybe it is still available:
https://www.cined.com/last-chance-cined ... ends-soon/

I wish people would stop using Blackmagic Disk Speed Test utility. The camera's USB ports only support USB 3.0 thus will never reach the speeds reported on the PC.

You need an adapter that is fast under USB 3.0 or an USB drive that is fast under USB 3.0

As it stands with the Sandisk Extreme Pro Portable SSD V2, it is only supported up to:

The following USB-C dives are recommended for recording 6K (Open Gate) Blackmagic RAW 5:1 up to 36 fps and 6K DCI Blackmagic RAW 5:1 up to 48 fps.

https://www.blackmagicdesign.com/support/faq/59043