1.0 controller API

[Wim Taymans]

On 04/23/2012 09:46 PM, Stefan Sauer wrote:
> On 04/19/2012 09:43 PM, Stefan Sauer wrote:
>> Hi developers,
>   ping?
>
> Stefan
- make 2 apis

- the controller returns the value of the first control point

Wim
>> 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
>>
>> _______________________________________________
>> gstreamer-devel mailing list
>> gstreamer-devel at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
> _______________________________________________
> gstreamer-devel mailing list
> gstreamer-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel