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IDProjectCategoryView StatusLast Update
0001267DCP-o-matic[All Projects] Bugspublic2019-11-20 11:58
Reportercarl Assigned To 
PrioritynormalSeverityminorReproducibilityhave not tried
Status newResolutionopen 
Product Version 
Target VersionFixed in Version 
Summary0001267: Investigate problems around 250Mbit/s

Not sure if I've checked that DCP-o-matic doesn't go over 250Mbit when you ask it for 250... worth checking if we can legitimately blame servers for problems at high bit rates.

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related to 0001664 new Check that J2K frames are not too large 



2018-04-16 14:33

manager   ~0002374

Last edited: 2018-04-16 19:01

View 4 revisions

There is probably something to investigate - in 'earlier times' I did some compression tests with 2k and 4k noise patterns. I just recreated such a 4k noise pattern in Photoshop, and did some compression tests with DCP-o-matic 2.12.4. This pattern is very complex and brings every common compressor to it's knees.
Created a 10s still DCP from it. These numbers are for the J2K MXF file:

2k - 125Mbit/s-24fps: 156MByte/124MBIt/s
2k - 230Mbit/s-24fps: 287MByte/229MBit/s
2k - 240Mbit/s-24fps: 300MByte/240MBIt/s
2k - 250Mbit/s-24fps: 312MByte/249MBit/s
2k - 250Mbit/s-48fps: 312MByte/249MBit/s
4k - 250MBit/s-24fps: 250MByte/200MBit/s
4k - 250MBit/s-48fps: 250MByte/200MBit/s
4k - 500MBit/s-24fps: 250MByte/200MBit/s
4k - 500MBit/s-48fps: 500MByte /400MBit/s

The standard size of 312MByte at 250MBit/s/24fps/2k computes to 249MBit/s - nice one.

It's a bit strange (though at least safe) that the 4k/24/500MBit/s doesn't nearly reach the target size, but the 48fps version does.
It's possible, though, that my test image does not really allow to saturate the 500MBit/s at 24fps, I may need to investigate this. It's just my assumption that this noise pattern is worst case. I tried to replicate this by using a high-res nature image, and applying noise to it. That created a more widespread color spectrum in video analysis, but still gave the same result at around 200MBit/s.
Maybe this is an OpenJPEG implementation issue with the cinema profiles. Is it at all possible they may not support higher Bitrates?

Hmm, interesting, I just tried it with the same image in DCP-o-matic 1.83.0 (YES!!!!), and it creates a 625MB file (10s-4k/24fps/500MBit). That computes to...
500MBit/s ... hmmm... maybe the 4k modes need some tweaking.

  • Carsten

Issue History

Date Modified Username Field Change
2018-04-05 15:45 carl New Issue
2018-04-16 14:33 Carsten Note Added: 0002374
2018-04-16 15:15 Carsten Note Edited: 0002374 View Revisions
2018-04-16 15:24 Carsten Note Edited: 0002374 View Revisions
2018-04-16 19:01 Carsten Note Edited: 0002374 View Revisions
2019-11-20 11:58 carl Relationship added related to 0001664