Data Rates on Black Magic Design camera

[Raj Peddinti]

Hello All

So on this link it says "Rates: 5 MB/frame in RAW 2.5K fits about 30 minutes of 24p video on a 256 GB solid state disk - compressed HD formats fit more than 5 times the amount of RAW video "

http://www.bhphotovideo.com/c/produ...ic_Design_BMD_CINECAM26KEF_Cinema_Camera.html

As far as I know epic 4k 2:1 rc3:1 256gb ssd lasts for ~45mins.

And scarlet's data rate is 55 MB/sec. Per blackmagic, the size of a frame on BMC is 5MB so for 24fps it has to record 120MB/sec. Am I missing something?

Raj

 

[Jason Murphy]

It's uncompressed RAW, not wavelet compressed like RED does. Much, much higher data rates.

REDCODE is a pretty spectacular thing.

EDIT: Noted some pretty confusing wording there, the compressed HD formats aren't RAW; this blurb makes them sound like they might be.

 

[Raj Peddinti]

It's uncompressed RAW, not wavelet compressed like RED does. Much, much higher data rates.

REDCODE is a pretty spectacular thing.

EDIT: Noted some pretty confusing wording there, the compressed HD formats aren't RAW; this blurb makes them sound like they might be.

Okay got it, thanks. If my understanding of what you said is right: as rc 3:1 records 45min in my example, uncompressed RAW is 3 times the rc3:1 and it will give 256gb ssd a recording time of 45/3 = 15 mins.

When you said "confusing wording", did you mean "compressed HD formats fit more than 5 times the amount of RAW video"

?​

It seems they are afraid about people getting frightened seeing the 256gb-30min number and they are specific about mentioning HDs and 5times recording blah blah...High data rates are bad in their own way, lol.

Raj

​

 

[Raj Peddinti]

One more question may be a dumb one, If giving high data rates such 12MB/s is not an issue for BMC, why did they constrain them selves to 30fps?

I can understand the complexity of giving uncompressed Raw and over cranking but what about beyond 30fps on pro-res and DNxHD formats?

Raj

 

[Tom.Wong]

One more question may be a dumb one, If giving high data rates such 12MB/s is not an issue for BMC, why did they constrain them selves to 30fps?

I can understand the complexity of giving uncompressed Raw and over cranking but what about beyond 30fps on pro-res and DNxHD formats?

Raj

i think that's a question best left to ask BM directly, but just for the sake of your curiosity, they probably don't have the processing power to get that read out faster than 30 fps, nor could the off the shelf ssd storage sustain 48-60 fps overcrank with cinema dng files.

 

[Mike P.]

In interviews they have said they are shipping with ISO400, 800, 1600 and frame rates 24/23.976 and 30/29.97, but that those shooting options will undoubtedly improve as time goes on. At one point they even talked about using more of the sensor (e.g. 4:3 for Anamorphic, etc.) Whether they charge for the firmware upgrades is yet to be seen, but seeing as how they give away Resolve Lite, cut down regular Resolve to under $1G, and are selling the camera for under $3Gs, the updates may be free as well... I definitely wouldn't expect more than 60p (especially CinemaDNG, which would need 300mb/s sustained... ProRes/DNxHD most likely).

 

[Alexander Ibrahim]

I saw some of the same interviews Mike mentions. I can confirm his point that they have publicly said that they wish to enable more features in answer to questions about frame rates ... right now they are concerned with delivering a stable camera.

WHAT FOLLOWS IS JUST CONJECTURE ON MY PART.

I am not connected to Black Magic other than being a customer. I'm just making guesses based on what little I know of the engineering of these systems. That's an educated guess, because I studied computer science and electrical engineering in university. The main word remains GUESS.

So ... I expect more from the camera over time. I expect them to release firmware updates for free that enable new functionality, just like they do for their other stuff.

I expect that for RAW video the disk interface is the main limitation. So how fast is the sustained write on a single SSD?

The fastest a quick search turned up on the site Storage Search was a Vertex 4 on SATA 3 at 535MB/s. That's peak read speed.

According to the OCZ Vertex 4 site, it sustains 462MB/s write.

Leaving a 20% overhead, I think they could write around 72fps in CinemaDNG ... but that is edge performance. I'd expect that to be reliable only for as long as it takes to fill the cameras buffer. I am guessing thats no more than 60 seconds, and probably more like 30s.

60fps is more likely for mainstream usage.

Even so, shooting 60fps will require you to test your drives and such for the foreseeable future. Basically for now it means buying only the fastest performance SSD drives, like the Vertex 4.

Looking at the camera's lack of heat management, I would bet that there will be thermal issues if you push the system that fast. I wouldn't expect to be able to shoot a whole project at 48 or faster. It should certainly be usable as a high speed rate in the context of normal 24fps photography.

For ProRes or DNxHD, they'll be processor limited. It's possible that they picked a commodity processor+GPU combination that can compress those codecs very quickly ... something similar to what is in the iPad 3. Of course very fast in these systems, is pretty darn slow compared to what a Mac or Windows computer can push with Mercury on Adobe Media Encoder or Resolve.

My guess is that 48-60fps would be a huge achievement in compressed codecs in that camera.

What I am really excited about is the next generation of Black Magic Cinema cameras. They'll learn a lot from seeing it in use, and they'll learn (the hard way) why Red does some of the things it does.

 

[Petr Dvorak]

What I am really excited about is the next generation of Black Magic Cinema cameras. They'll learn a lot from seeing it in use, and they'll learn (the hard way) why Red does some of the things it does.

+1 ;o)