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

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

Post by Seppia »


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 :

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 (308.11 KiB) Viewed 1853 times

The SRT is set not to be burned-in, to avoid video encoding :
DCP-o-matic_subtitles_soft.png (468.64 KiB) Viewed 1853 times

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 ?

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

Post by 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
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Re: Re-use DCP to add soft subtitles - passthrough video ?

Post by 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 I can take a look.
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