Clip layering

  • pieterb

    pieterb - 2013-05-02

    Hi there AAF developers,

    I've been looking into AAF for a while now.
    I wonder if it's possible in AAF to have an overlap of two (or more) SourceClips without having to combine them with a Transition effect. A possible (dirty) alternative could be a Transition with a two parameter audio dissolve that has an ingoing level of 1 and an outgoing level of 0, or vice versa. I don't quite understand the concept of NestedScope and ScopeReference, could this provide a way to implement multiple clip layering?

    Thanks in advance,


  • astan

    astan - 2013-08-01

    I believe it is possible but only 1 will be visible. I think source clip tags can be nested to accommodate this

  • Jim Trainor

    Jim Trainor - 2013-08-01

    The clips in a sequence cannot overlap without a transition between them.

    You can put an effect (OperationGroup) in a sequence and that can reference more than one clip. What the operation does depends on its definition. It can be what ever you want. Of course, if you go outside the standard effects nobody else will be able to read it.

    A NestedScope is used to create composited layers.

    I didn't see your post when many months ago when you made it originally, only when astan replied. Sorry.

  • pieterb

    pieterb - 2013-08-08

    Thanks for the reply, in the meantime I got to understand the mechanism of NestedScopes and ScopeReferences. They provide a way for clip layering, but the interpretation is application-dependant. Some applications just treat ScopeReferences as fillers and accumulate all NestedScope slots into a single track, others calculate the output of the NestedScope as is proposed by AAF.

    Anyway, I think the big issue with AAF is that there's too many room for dialects and misinterpretations due to incomplete and obscure documentation.

  • Jim Trainor

    Jim Trainor - 2013-08-08

    There shouldn't be too much variability in how NestedScopes are interpreted. I think the spec is clear. The variability you are describing is application behaviour not necessarily indicating a problem with the structure of the file. But it is not always clear and in general it is true that there is too much variability. The following specification attempted to bring some order, it is not universally followed:

    There is a utility in the SDK called the "AAFAnalyzer" that will test your file compliance with that specification.

  • pieterb

    pieterb - 2013-08-08

    Yes, I'm very much familiar with the AAF edit protocol. I have developped an AAF import/export plugin for our DAW, and I try to stick to it as much as possible. Still, even with the AAF spec and the edit protocol, there are some things that remain unclear. I'll try to summarize them in a new thread.

    • John Emmas

      John Emmas - 2013-08-08

      On 08/08/2013 10:02, pieterb wrote:

      Yes, I'm very much familiar with the AAF edit protocol. I have
      developped an AAF import/export plugin for our DAW

      Hi Pieter,

      Just out of interest, what DAW do you work on? I also work on a DAW
      called Mixbus so it's nice to see a kindred spirit.!



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