BMPCC 4K bit rates compression qestions for comment

[cyvideo]

Was just wondering what forum members are thinking about the compression rates on the new BMPC 4K. A lot of us like ProRes but at the published bit rates for the 4K, if correct make me think that the BMPC 4K has a compression ratio at its highest bit rate of 7.14:1 compared to Apple's published 4K bit rate white paper. This is indeed a very high compression ratio.

The published BMPCC 4K bit rates are as follows:

Storage rates are as follows (for 30p. In 24p, will be slightly less)…

4096 x 2160
CinemaDNG RAW – 270 MB/s
CinemaDNG RAW 3:1 – 128 MB/s
CinemaDNG RAW 4:1 – 96 MB/s

That’s approx. 5.8GB per minute in DCI 4K RAW 4:1.

3840 x 2160
Apple ProRes 422 HQ – 110 MB/s Apple ProRes 422 – 73.6 MB/s
Apple ProRes 422 LT – 51 MB/s
Apple ProRes Proxy – 22.4 MB/s

Let's take the BMPC 4K Apple ProRes 422 HQ at 110 MB/s. Compare that to Apple's published bit rate for HD 422 HQ which is 220 MB/s.

Am I to gather from these figures that we have 220 MB/s for HD 422 HQ and only 110 for UHD 422 HQ? If this is the case then it is very highly compressed on the BMPCC 4K.

Apples published ProRes 4K white paper state that ProRes at 30p UHD in 422 HQ is 884 MB/s which is 398 GB/h

ProRes 422 HQ is a DCT-based intra-frame-only codec which at 4K 110 MB/s is going to be well under anything we have seen in UHD ProRes in the past. In HD terms this is a bit rate equivalent of 27.5 MB/s, AVCH type bit rates. Bare in mind AVCHD at those sorts of bit rates is a long GOP codec which has greater efficiencies than intra frame at the same bit rate.

My question is how will this UHD 110 MB/s codec stand up in heavy grading?

I'm happy with progressive HD 422 HQ at the respective bit rates of 367 MB/s for 50Hz and 440 MB/s for 60Hz but 110 MB/s for UHD?

I guess only time will tell when we can get the codec on the timeline.



Chris Young

 

[Thomas Smet]

ProRes is ProRes and cannot use a different data rate than what Apple specifies for that level. Be careful not to confuse mbps and MB/S. There are 8 mbps in a MB. Its a goofy value that throws off a lot of people. 220 mbps is 27.5 MB/S. Compare that to the 110MB/S BMD published and you get the 4x size.

 

[jb.]

110MB/s is 880Mb/s which is the standard 422HQ bitrate for UHD. Blackmagic are giving their data bitrates in MegaBYTES not MegaBITS.

 

[cyvideo]

Thanks for pointing out my error guys. I should have been awake to that as I do know the differences between the two. Not concentrating I think

Chris Young

 

[Ken1212]

I would like to see the addition of .MP4 options to make it more diverse.