Question on Transcoding/Encoding

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peter
Posts: 3
Joined: Sat Jun 01, 2019 9:30 am

Question on Transcoding/Encoding

Post by peter » Sat Jun 01, 2019 9:35 am

Hi,

New to DOM... really great tool! I'm making a DCP now.. and I see in the message area that it is 'Transcoding'. It lists the 'Encoding' percentage and the frame it's on. I'm trying to figure out what it's doing right now. Will is always show a message like that?

I believe my assets were already DCI compliant.. so it shouldn't need to Transcode anything. I had 2 Wave files (24bit, 48khz) and a folder of j2k files (encoded with Assimilate Scratch.. using DCI JP2000 format). Maybe that message doesn't necessary mean it's transcoding the video? Just encoding into a MXF file (or does it say something else when creating the MXF files)?

Any tips on those messages would be helpful. No point in making j2k files twice.. just want to make sure I'm doing it all right. I don't have any of the boxes checked to 'Re-encode' files.

Thanks much,
Peter

Carsten
Posts: 1240
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: Question on Transcoding/Encoding

Post by Carsten » Sun Jun 02, 2019 1:22 am

You probably have set a container size/resolution that is different from the format of your J2K files - in that case, transcoding needs to happen to create the necessary container size. That ist, for 1998/1080 J2K, you would set the Container to 2k flat, for 2048/858, to 2k Scope.

Normally, DCP-o-matic does not recompress J2K image series or MXF wrapped J2K. However, you then have to make sure the j2K or MXF data is DCI/DMPTE compliant yourself. Some software packages create valid J2K or MXF, but still a DCP that crashes.

- Carsten

peter
Posts: 3
Joined: Sat Jun 01, 2019 9:30 am

Re: Question on Transcoding/Encoding

Post by peter » Sun Jun 02, 2019 7:32 am

Thanks for the info.

I just double checked. My J2K's are 1998x1080 and I've got my DCP container to Flat. So that can't be it. Would it recompress if the data rate isn't exactly the same? I might have made the J2K's at 150 Mb/sec and the DCP settings might have been set to 125. I don't have the re-encode box checked.

These J2K's from Scratch should be DCI compliant.. at least when I used that program to make DCP's (using OpenDCP), they always played fine at various theaters and festivals.

The Transcoding/Encoding stage didn't take too long (maybe 30 mins or so).. so doesn't seem like it actually re-compressed the video. This is a 75minute feature project.

What else could it be doing at that stage? Could it actually just be wrapping the J2Ks into an MXF file.. but it calls it Transcoding/Encoding?

thanks,
Peter

Carsten
Posts: 1240
Joined: Tue Apr 15, 2014 9:11 pm
Location: Germany

Re: Question on Transcoding/Encoding

Post by Carsten » Sun Jun 02, 2019 10:14 am

What type of CPU do you use? I'd say 30min for a 75min feature should indeed indicate that no recompression took place, only wrapping/hashing. 'Transcoding' is universal, maybe at one time Carl could change this indication to 'Wrapping' if J2C or MXFs are reused.

The compression rate setting becomes irrelevant for J2C and MXF wrapped J2Cs (as long as you leave 'recompress' unticked).

- Carsten

peter
Posts: 3
Joined: Sat Jun 01, 2019 9:30 am

Re: Question on Transcoding/Encoding

Post by peter » Sun Jun 02, 2019 12:51 pm

I have a 2010 Classic Mac Pro (dual 2.66 6-core CPUs). I think initially it took like 4-5 hours to make the J2K files.. that's why I figured it wasn't fully remaking those. Since it's the first time using DOM... I just wanted to make sure I was following the correct workflow steps. I usually like to make the J2Ks in Scratch since it gives me a bit more control.. and since I believe those are DCI compliant.. it seems that DOM would be ok with those and it would go pretty quick (which it did).

I appreciate all the help on that.

-Peter

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