Re: [ecasound] chain setup equivalence

[Kai V. <kve...@ec...>]

Hi,

On Sun, 6 Dec 2009, Joel Roth wrote:

>> I wonder if these two lines are equivalent:
>>
>> -a:1,2 -i:something
>>
>> -a:1 -i:something -a:2 -i:something

you replied to yourself already, but just you confirm that no, those are 
not equivalent. Every '-i' and '-o' is a separate "add input/output" 
actions. So the former adds one input to two chains, while the latter adds 
two separate inputs (that both happen to be labelled 'something') to two 
chains.

> Attempting to answer my own question, the following
> is valid:
>
> -a:1 -i:foo.wav
> -a:2 -i:bar.wav
> -a:1 -o:null
> -a:2 -o:null

Yes, this is valid, but note that two independent instance of 'null' are 
created. "-a:1,2 -o:null" is different in that only one 'null' object is 
created.

> But not this:
>
> -a:1 -i:foo.wav
> -a:2 -i:bar.wav
> -a:1 -o:loop,1
> -a:2 -o:loop,1

This fails as 'loop' object raise an error if one tries to create multiple 
loops objects with the same id (same same direction).

> You would need to say:
>
> -a:1 -i:foo.wav
> -a:2 -i:bar.wav
> -a:1,2 -o:loop,1

Or:
  -a:1 -i:foo.wav
  -a:2 -i:bar.wav
  -a:1 -o:loop,1
  -a:2 -o:loop,2

Now create two 'loop' objects is ok as they have unique id's. But of 
course, usually you specifically want to attach the chains to the same 
loop object instance (and thus "-a:1,2 -o:loop,1" is what you want).

...

The reason why this works like this is to make it easy to specify all 
routing (also the complex types) on the command-line. Well, not 100% sure 
about "easy", but at least with less typing. ;) One important bit is the 
this syntax for linking an input/output to multiple chains, while still 
allowing to have multiple instance of similar objects (e.g. multiple 
independent inputs reading from the same file).

The approach is on purpose different than in gstreamer (how one connects 
pads of gstreamer pipelines when using gst-launch) and JACK port 
connections.