Gnolin - Notes and Clarification

[Edward Hervey]

On Fri, 2011-02-18 at 11:32 -0800, Matt Veenstra wrote:
> I want to confirm my understanding about the relationship between
> Gnolin elements and timelines.
> 
> This is what I understand and may be useful for other beginners
> searching the archives.
> - Each "gnlfilesource" must contain only one stream and you must set
> the caps to pick the stream on a multi-stream file source.

  Yes. This is generic in fact to *any* gnlobject (gnlsource,
gnloperation, gnlfilesource, gnlurisource and gnlcomposition).

>   A/V only
> to my knowledge.

  No. It can be any format.

>   I am not sure caps could handle a file with multiple
> audio streams for example.

  That's a generic problem with being able to identify streams. We're
missing a generic system in GStreamer for that.

> - "gnlfilesource" is it self a simple helper function and can be
> duplicated with "gnlsource" and the proper standard gstreamer filesrc,
> decode bin, etc.

  Correct.

> - "gnlcomposition" is a group element to hold multiple streams of the
> same type (audio streams, video streams, etc).

  Yes (for 99.99999999% of the use cases).

> - You need 2 "gnlcomposition" one for audio and one for video if you
> are using "gnlfilesource".

  If you want to have audio AND video as the outputs yes. Otherwise, you
have no obligation. An audio-only editor will only use one composition.

> - You can do simple tests with just "gnlfilesource" without the
> "gnlcomposition" when using only one source file.

  Yes. That extends to gnlsource

> - If you want to use "gnloperation" you must do this in a
> "gnlcomposition"

  Yes.

>  generally between 2 "gnlsource"

  you can just have a gnloperation over one source.

> 
> Questions.
> Is the master timeline the pipeline itself?

  There is no concept of Audio/Video 'timeline' in gnonlin, only
compositions.

  I believe what you are referring to as 'timeline' is the combination
of one or many gnlcompositions (one for each media type).

> If I have 2 "gnlcomposition".  With different file sources in each
> composition that have the exact same start and duration times, am I
> guaranteed that these will be perfectly in sync?

  Yes.

> 
> Thanks for reading and helping with the questions.  This information I
> felt was missing as I started.  Maybe it was because I did not know
> where to look.

> 
> Matt Veenstra
> tribalmedia
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