Validation Error on Frame size

[stephenv2]

I'm a seasoned DCP creator and evaluating DCP-o-matic. It's worked well on a couple of short 2K, 5.1 DCPs. Just did a 4K feature, 5.1 and player validation failed reporting at least one frame over the 250 Mb/second limit.

However, I create my own J2K files and set a custom data rate of 240 Mb/s and I also pulled up my folder and the largest files are no larger than 1281 KB which is exactly 240 Mb/s at 24fps.

Something must be wrong in the code math for verification.

[carl]

Hi, are those 1281KB files 1281000 bytes long, or 1311744 bytes long? I.e. on your system is a KB 1000 bytes or 1024?

[stephenv2]

Windows 10 64-bit is the system. 1281 KB is the reported size in Explorer. If you right click you get 1.25 MB (1,310,832 bytes).

That's well under the byte limit and according to Dolby techs from a high rate discussion from some years ago:

Further notes from other Dolby technicians below I got via email.

"The max size for 2D is: 1572864, 3D per each eye is: 786,432 (1,572,864 L+R, based on SMPTE 429 max "compressed rate" total). THIS VALUE HAS LIMITS IN HARDWARE AND CANNOT BE EXCEEDED"

[carl]

DoM is using the SMPTE Bv2.1 recommended values (or should be!)

For a frame rate of 24FPS, a 2K distribution shall have a maximum of 1,302,083 bytes per frame (aggregate of all three color components including headers)

This corresponds to 1302083 x 8 x 24 = 249999936 bits which seems to make sense according to the 250Mbit/s limit I've often seen mentioned.

It's interesting that Dolby allows more...

[Carsten]

We have a lot of reports for classic Doremi (Dolphin boards) servers failing well below the official specs. It is not a good idea to use the maximum allowed values. A while ago, I experienced one of these Doremi crashes myself with a documentary created at 235MBit/s (my personal limit until that project). This played well on our own Sony and Barco servers, but crashed on a Doremi. There were indications that 235MBit/s for this DCP was 'just' a little bit too much (we could play most of it, but not everything).

I recreated the DCP at 210MBit/s, and had no issues then. It may not strictly be a matter of formal datarate, but also of certain image aspects (e.g. high detail, color components, etc.). But, to be on the safe side, I would suggest to use something in the 220MBit/s range if you expect your DCP to go wide.
It may also be that there are internal differences between certain encoders that may allow higher data rates. Dolby had their own mastering station, and it may be that their own encoder allowed higher compliant datarates than OpenJPEG does.

Initially, the 250MBit/s limit that was communicated for DCP was more targeted at RAID and bus transfer capability I think, not so much at J2K decoder specifics.

[stephenv2]

DoM is using the SMPTE Bv2.1 recommended values (or should be!)

For a frame rate of 24FPS, a 2K distribution shall have a maximum of 1,302,083 bytes per frame (aggregate of all three color components including headers)

This corresponds to 1302083 x 8 x 24 = 249999936 bits which seems to make sense according to the 250Mbit/s limit I've often seen mentioned.

It's interesting that Dolby allows more...

I'm not an expert but when I check every online calculator 1310832 Bytes = 10486656 Bits.

[carl]

I'm not an expert but when I check every online calculator 1310832 Bytes = 10486656 Bits.

I don't follow what you mean here, I'm afraid!

We have a lot of reports for classic Doremi (Dolphin boards) servers failing well below the official specs.

DoM also issues a warning at 230Mbit/s.

[stephenv2]

I'm not an expert but when I check every online calculator 1310832 Bytes = 10486656 Bits.

I don't follow what you mean here, I'm afraid!

[/quote]

The DCP data limit is "bits per second" not "bytes per second". All the bitrate calculators I can find calculate that my frame size is 240 Megabits per second. Your math above appears to be use my frame size in bytes to calculate bits per second.

I've used this 240 Mb/s for a couple of dozen different 4K DCPs that has played in numerous multiplex, giant screen and IMAX venues are multiple servers

[carl]

The DCP data limit is "bits per second" not "bytes per second". All the bitrate calculators I can find calculate that my frame size is 240 Megabits per second. Your math above appears to be use my frame size in bytes to calculate bits per second.

Your frame size is 1,310,832 bytes, I think? That is 1,310,832 times 8 = 10,486,656 bits.

If you have 24 frames per second, that is 10486656 times 24 = 251,679,744 bits per second.

The definitions of megabit are a bit confusing; some people say a megabit is 1,000,000 bits and some say its 1024 squared = 1,048,576

There's some discussion here.

The SMPTE Bv2.1 specifies a maxium of 1,302,083 bytes per frame, which corresponds to 10,416,664 bits per frame, or 249,999,936 bits per second. This is why your slightly larger frame is being flagged as "too big" by DoM.

I've used this 240 Mb/s for a couple of dozen different 4K DCPs that has played in numerous multiplex, giant screen and IMAX venues are multiple servers

It's great that it works, but at the moment (rightly or wrongly) DoM is sticking to Bv2.1 on this.

[stephenv2]

The SMPTE Bv2.1 specifies a maxium of 1,302,083 bytes per frame, which corresponds to 10,416,664 bits per frame, or 249,999,936 bits per second. This is why your slightly larger frame is being flagged as "too big" by DoM.

It's great that it works, but at the moment (rightly or wrongly) DoM is sticking to Bv2.1 on this.

I'm guessing the disparity is the J2K encoder I'm using is calculating per second as according to Dolby that bytes per frame is higher than than SMPTE Bv2.1 during any 24 frame second the aggregate is under this.

I will reach out to the J2K encoder and get their two cents on it.