[Documentation] Phonon

Matthias Kretz kretz at kde.org
Mon Jan 12 08:18:08 GMT 2009


On Saturday 10 January 2009 16:47:27 Georg Grabler wrote:
> I didn't know what crossfading is exactly, and I'm currently messing the
> first time with multimedia / sound at all. I think though, that google
> would have had a proper answer to what crossfading is.

It's as simple as fading one track out while fading another one in. The 
interesting part about it is to keep the resulting sound power constant which 
requires a special fade curve. But Phonon::VolumeFaderEffect already provides 
that curve for you. So if you get the timing of the faders right you have a 
perfect crossfade.

> On Fri, Jan 9, 2009 at 10:16 PM, Michael Pyne <mpyne at purinchu.net> wrote:
> > On Friday 09 January 2009, Georg Grabler wrote:
> > > 2.) Can I crossfade between MediaObjects in the Queue (as an example)?
> > > Like having 1 file playing, at aboutToFinish i set another file
> > > (mediasource)
> > > in
> > > the queue, and set the transition time to -5 (or any other value which
> > > seems to fit nicely). Wouldn't this mean, that I'd always need to have
> > > two
> > > mediafiles in the queue, since aboutToFinish is too short before the
> > > end
> > > of
> > > the track to make sense for crossfading (at the current behaviour I
> > > experience), and that the transition time would be a "global" value.

aboutToFinish is defined as being early enough to enqueue another MediaSource 
so that the transition still works. So if the transition time is negative 
aboutToFinish is emitted that much earlier.

> > setTransitionTime with a negative value should do crossfading according
> > to the API docs (I'm pretty sure there was no setTransitionTime when
> > crossfading was first added to JuK but I could be wrong). However the
> > docs warn this may not work reliably with every backend as well....

setTransitionTime has been there for a long time but isn't implemented for 
phonon-xine, and possibly never will be.

Matthias Kretz (Germany)                            <><

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