ideal bandwidth with prores material

[lestevennok]

Hi all,

First of all, thank you for this wonderfull application !

I use it to turn only ProRes materials to DCP.
And I wish to know what is the ideal bandwidth with ProRes materials.
I don't want to put a too high bandwidth because it can't be better than the original material...

I looked in the forum and I did not find the answer ... unless I searched badly ...

For example, I have 3 animated movies to transform into DCPs:
1. The first one is in HD ProRes 4444 about 230 Mbps
2. The second HD ProRes 422 HQ, about 180 Mbps.
3. The third HD ProRes 422 about 115 Mbps

Is there a way to know which is the best bandwidth to use?

For example :
1. set the bandwidth in DCP-o-matic at 230 Mbps
2. at 180mbits/s
3. at 115mbits/s

Or is there a calculation method to know the best bandwidth to use for JPEG2000 based on ProRes bandwidth?
Cross-multiplication for example? or maybe is a stupid question ?

Thank for yours answers !
Jim

[Carsten]

It is not possible to give a technically correct or precise answer on this, however:

- the actual datarate that goes into the file will usually depend more on image complexity than set datarate - the data rate should be considered as a max-peak setting
- as far as I know, Prores uses the same internal compression scheme (Wavelet) as JPEG2000. That doesn't mean they are identical, but as a rule of thumb, one could deduct from this that the J2K datarate should be roughly similar to the Prores datarate, or slightly higher.

Personally, I don't think much about DCP data rate setting. There may be applications where a specific rate/file size may be desirable - e.g. if a short must fit onto a specific size USB stick, or a feature onto a specific size/cost SSD.
But, typically, I set my default data rate to 230MBit/s and then forget about it.

- Carsten

[lestevennok]

Hi Carsten,

Thanks for your precise answer.
OK, so 230 Mbits/s for default data rate and slithy lower when the data rate of the original file is lower than 230Mbits/s.

Do you know if DCP o Matic will put a lower data rate than the one indicated if it sees that the chosen rate is too high?

Jim

[Carsten]

230MBit/s is my personal rule of thumb. Some servers are known to have problems if the datarate peaks around the 'official' DCI spec of 250MBit/s. So, 230MBit/s is reasonably safe to be played on all existing servers world wide.

If your material has a low complexity/level of detail, DCP-o-matic will not force the indicated data rate, but will 'naturally' create a file/section with a lower datarate. The extreme example is full black. You will also notice DCP-o-matic rushing through these parts during encoding, and becoming much slower with real images.

- carsten