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Question about CPL's FFOC offset value #7

Open cfadamp opened 1 year ago

cfadamp commented 1 year ago

My clients and colleagues are always confused about the proper usage of FFOC marker in the CPLs.

The spec says that If present, the value for FFOC should represent the first frame of the Composition and be equal to “1”.

but in the CPL this parameter is called "Offset" and should look like similar to this:

<Marker>
    <Label>FFOC</Label>
    <Offset>1</Offset>
</Marker>

I think the wording "Offset" is where the most of the confusion starts from.

So in our timeline representation the first frame starts from "0". Therefor in our world, in CPL the offset ="1" would mean that one should place the playhead at the second frame as you can see it in the picture below:

image001

Our clients would like to place the marker at the timeline at frame position 0 and have us to transform this number to "1" on CPL. My first problem with this is, then how to represent a marker at offset = "0" in a timeline? Is it even allowed by the specs? If it is not allowed, then it is an easy task for us to fix this issue.

Does the specs describe that FFOC offset="1" means placing the marker at the frame position 0 or at frame position 1 on the timeline?

Thanks!

SteveLLamb commented 1 year ago

Yes, I agree this is terribly confusing and also believe "offset" should be zero-based (frame count non-inclusive), not number of frames. This is also part of a larger discussion @dcbullock and I have had a few times, and as such put in an issues on ST 429-7 https://github.com/SMPTE/st429-7/issues/6