Cropping & Encode Servers

[Kewl]

When to make a DCP with encode servers, DOM has to crop the source video, where is that cropping taking place? In the DOM host before sending to the DOM encode servers, or in the encode servers? From anecdotal evidence (cropping in DOM vs using cropped source file), I would say the cropping is done in the encode servers, but i just want be sure.

In any case, for a UHD Scope source video, making the DCP from a cropped source file, I gain around 5 fps, from an average 17 fps to 22 fps. In our DCP making setup, the bottleneck is the network bandwidth from the host to the encode servers, topping at around 500 MB/s. That's why I deduce that sending already cropped frames (from the source file) will allow sending more frames per second.

[carl]

Correct, the crop happens on the encode server. The main DCP-o-matic instance decodes the video, then sends an uncompressed bitmap (with some metadata, like how it should be scaled/cropped etc.) to the encode server. That sends back JPEG2000 data.

One day it would be interesting to try sending the raw compressed stream to each encode server, so that it can decode the video. It's a duplication of work, but most video decoders are quite efficient, and network saturation is often the first bottleneck that people hit, I think.

[Carsten]

I guess, most of the time cropping will not improve throughput much, because only small parts of source images will be cropped. The common exception of course ist letterboxed scope.

[Kewl]

Correct, the crop happens on the encode server.

OK, thanks for confirming. So, clearly from my tests with HDR UHD sources, cropping the source will both speed up the HDR to SDR conversion stage and the DCP making stage. Less pixels to process...

[Carsten]

That's obvious when you talk about the whole processing pipeline. I just doubt that it has a major impact on network saturation when using encode servers. But of course, the effect grows larger with 4k sources.


- Carsten

[Kewl]

I just doubt that it has a major impact on network saturation when using encode servers. But of course, the effect grows larger with 4k sources.

Well, as I observed in our setup, the gain in encoding speed for a 2.40:1 letterboxed UHD was around 25 to 30%. Not negligible...