1.0 controller API

[Stefan Sauer]

On 04/19/2012 09:43 PM, Stefan Sauer wrote:
> Hi developers,
 ping?

Stefan
> right now the gst-plugins-base/tests/check/elements/volume test is
> failing. It is not just the test, actally using the volume element wit
> gst-controller is broken. One thing that is special here is that volume is
> checking if the mute and/or volume property is controlled and if so, it
> is fetching blocks of control-values to apply them in a scalar
> operation. This way one can have a control resolution down to
> sample-rate (which is rarely needed).
>
> In 0.10 the value_arrays where wrapped as a GstValueArray which was
> nasty for bindings. The good thing for elements written in C was that
> you e.g. got an plain array of doubles which was ready to be used.
>
> In 0.11/1.0 we fill a array of GValues, which is nice for bindings, but
> bad for e.g. the volume element.
> One way I can fix this is to change the API to have two entry points -
> one for C and one for bindings:
>
>    gst_control_binding_get_value_array(GstControlBinding * self,
>       GstClockTime timestamp, GstClockTime interval, guint n_values,
>       gpointer values);
>    gst_control_binding_get_g_value_array(GstControlBinding * self,
>       GstClockTime timestamp, GstClockTime interval, guint n_values,
>       GValue * values);
>
> (I would rename the current function and introduce a new one under the
> old name). Implementationwise I can require controlbindings to support
> it and wrap it on the control-bindings baseclass, with performance
> penalty for the bindings (extra conversion).
>
>
> Another 'issue' I'd like to get some feedback from what behavior people
> would expect is the following. Again, an element/application requests an
> array of control values from a certain starting point. What if the
> controller has the first defined control-value (e.g. a time-based
> controlpoint) after the start of the requested region? Right now
> interpolation control-source returns NaN for time-ranges with no control
> curves defined (for single values it returns false). For arrays the
> method returns false if it would be completely empty. If it is partially
> filled, one gets NaNs on the control-source array and empty GValues on
> the bound value-array. One alternative on the control-binding level
> would be to use a) the current property value, b) the default property
> value. a) has the advantage that setting it would be kind of neutral,
> but the disadvantage that it could have changed inbetween. b) sounds
> like a worse choise to me.
> We could also assume that if the first defined control-value is at ts>0
> that the same value applies to earlier timestamps. This would be
> symmetric with keeping that last value of later timestamps.
> That would only leave the error case where no single control-point is
> set and thats imho just an error.
>
> Stefan
>
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