Re-use DCP to add soft subtitles - passthrough video ?

[Seppia]

Hello

Using DCP-o-matic 2.12.20 on macOS, I want to add a subtitle file to an existing DCP. I don't want to make a VF DCP, but a new OV DCP by re-using the existing audio and video MXF from the current DCP. I'm in the second case "Making a complete DCP with projector-added subtitles" of the manual :
https://dcpomatic.com/manual/html/ch16.html#idp39.

I make sure not to change anything on the audio and files (zero crop, zero scale, no color-profile change, same container ratio, same framerate, same audio channel assignations, same level, ...) :

DCP-o-matic_reuse_resssource.png

The SRT is set not to be burned-in, to avoid video encoding :

DCP-o-matic_subtitles_soft.png

Yet, when building the DCP, it seems DCP-o-matic transcodes the ressources : there's a long "Encoding" process taking place on DCP generation.

My question is : when re-wrapping an existing DCP (to add soft subtitles for example), how can I be absolutely certain than DCP-o-matic passes through the ressources without transcoding/re-encoding them again ?

Thanks

[Carsten]

Basically what you did should work. But maybe you can attach your project file here or send it to Carl - maybe there IS something set so that DCP-o-matic is forced to reencode. Normally, the speed difference between rewrapping and reencoding is enormous. When creating a new subtitled OV, the time needed should only be the read/write speed of your source and destination media.

- Carsten

[carl]

There's an open bug to suggest making DCP-o-matic clearer about what it's doing with "passthrough" (including reasons for why it might not be).

If you can send the metadata.xml and log files from your project to carl@dcpomatic.com I can take a look.