Exchanging a Video part in an existing DCP

[freezer]

Hi all,
long explanation here at the top and brief TL'DR at the bottom:

Long version:
Setup is DCP-o-matic 2.16.39 (a tried and tested version for years, so I am hesitant to update)
DCP is an unencrypted SMPTE 2k scope FTR video with 5.1 audio
Created from a 12bit DNxHR 2k scope MXF master file.
Audio master is a 5.1 32bit BWAV file.

As always DCP-o-matic created a flawless DCP I had uploaded for cinemas last week. Test screening is scheduled for upcoming Thursday, film premiere will be on Oct. 23rd.

Now out of a tragic incidence I was tasked today to make a few last minute changes in the end credits.
Made the changes in Resolve, exported the new end credit part.

As I've already researched and read here on the forum, it is possible to re-insert/trim parts in DCP-o-matic.
My idea is to save on encoding time and just have to re-encode the new end credits. No version file planned. Just a new DCP, saving render time.

Here is what I have tested:
I duplicated the existing DCP-o-matic project to test things out. Imported the MXF with the new end credits. Trimmed the old master mxf. Everything went smooth, checked the timeline. Only when starting to export as a new DCP, silly me realized that this of course means a complete re-encoding.
So canceled export.
Imported the existing DCP, did trim that again. But now it seems I can't separate the DCP audio from the video - so both get trimmed. Well then replace the audio too with the master source - so I thought. But then the DCP-o-matic timeline went crazy and I couldn't get it back to work - only small parts of the DCP video track got shown - having the same length as the new end credits. Both video tracks sat at the same timeline position, the master audio track below in its full length. Now I couldn't get the full length of the DCP video track back - regardless of what I did in the trim.

I don't know if I just put myself somehow in a corner by a wrong approach, so ditched the whole thing and started over fresh.
To get the job done I have now running a DCP export from a full new MXF video master as I do not want to risk any troubles later on.

But for future reference I really would like to get a clue what I might have done wrong here
and how the correct procedure would have had to look like.

In short:
* existing unencrypted DCP (video & audio)
* master video file with new end credits
* trim from the end of the DCP and insert new video part only
* export as new DCP and save render time by encoding just the new video part and re-use existing DCP audio

What is the correct way to do this successfully without messing up?
Thanks for any input

[IoannisSyrogiannis]

Does it -indeed- mean a complete re-encoding?
Or does it mean a re-packaging?

If you have had the original project cloned, use that, the original. Unless you have checked the specific box on encoding, DCP-o-matic will not re-encode what it has already done. It will only re-package the previous work.

That with trimming is the case (for better or for worse), but you can re-import the audio mxf as well, and trim it as you prefer and as it works for you.

Good luck and let us all know if it worked.

[freezer]

Thanks. Found some time now to redo this for testing purposes.

The main issue is that there is no way to remove or deactivate the DCP audio track in the timeline.
And my confusion came from the fact that when you re-order the files in the content window it will affect the placement on the timeline. So when I moved the DCP down in the list it attended the whole file at the end of the timeline...
That was quite confusing and unexpected.

• I made another duplicate of my original DCP-o-matic project.
• Deleted the MXF video master, but kept the WAV audio master.
• Then imported the DCP with the old end credits.
• Trimmed that down to exclude the old end credits.
• imported the new end credits MXF
• selected all files in the content list and switched to the timeline to check the correct order and placement (you can grab a clip and move it around in the timline)
• exported as a new DCP which did only newly encode the end credits from its master file
• checked the new DCP in the DOM-Player -> new end credits are there and audio is also there

So in the end it worked as intended, but the interface could be improved a bit here to prevent user confusion.
For example it should be possible to deactivate a track in the DCP for the user - so it is clear to the user it won't get used.

Step_01.png

Timeline_original.png

Step_02_importDCP.png

[freezer]

Timeline_DCP.png

Timeline_trimmed.png

Step_03_addedNewEndcredits.png

[freezer]

Timeline_final.png

[freezer]

OK - we tested that now in a local cinema.

With catastrophic results.
Because DCP-o-matic did sum up the WAV audio track into the DCP audio track without telling that it would do that.
Now we have a DCP with extreme and clipped audio levels
How could a user have to expect such a illogical behavior?
And all because it was not possible to just deselect or remove or unlock the audio track from the imported DCP in the timeline.

What is the purpose here of summing up audio tracks when creating a DCP?

[carl]

The thinking here was that you have two audio tracks in your timeline, so why wouldn't they both be included?

The most common use-case is to allow one WAV file per channel for the audio.

If I understand right, you wanted to remove the DCP audio from the timeline but found no way to do it? I agree that this could be improved.

[freezer]

I had to patch a few seconds at the beginning and the full end credits at the end of the DCP.
When importing the DCP there is no way to remove or deactivate its audio track.
And there is no way to lay the patch clips over the video track - they get added to the length.
So the only option is to trim the DCP and put the patch clips in place.
But because DCP video and audio can't get separated - audio gets trimmed too.
So I had to add the full audio master track again.

When creating the patched DCP DOM did sum up both audio tracks in each channel, instead of overwriting them.

[carl]

You can remove the DCP audio by unmapping all its channels in the audio tab. I agree this is not obvious when you are using the timeline.

It should also be possible to lay patch clips over the main DCP. What happens when you try?

In general I agree there are some parts of the timeline "user experience" that could be better.

[freezer]

Ok, the hint with unmapping all audio channels of the DCP is gold - but super not obvious...

I have now tested this with a new project.
Added the DCP.
Added Intro patch clip.
Added Endcredits patch clip.

Put the DCP in the list to the lowest.

Placed the patch clips in the timeline over.
Suddenly the patch clips are shown below the DCP but in the preview it seems right.
That is contrary to any user experience in any other software or like things would work in real life - that clips below another clip are the ones dominant and on top for playback now:

Timeline_DCP_and_Patches.png