Hello,
the patch "filter-apply, ladspa-sink, virtual-surround-sink:
filter-apply supports
ladspa-sink and virtual-surround-sink" by JeongYeon caused some discussion
between him, Arun and me on how to handle filters in a more general case.
Here is the result:
1) Generally, we have three different classes of filters:
a) device based -> all streams that use the master sink/source are
filtered
b) stream based -> only a single stream is filtered
c) stream group based -> groups of streams are filtered
2) For device based filters, all streams that exist on the master sink
should be moved to
the filter sink when the filter is inserted. The master sink should then
effectively be hidden
in the sense that any stream that tries to use the master sink will be
redirected to the filter
sink.
2) The same filter (for example an equalizer sink) might be used in any
of the classes
described above and there may be multiple instances of the same filter
(for example
two equalizers for two different groups of streams). This means the
filter class must
be given as a property when the filter is loaded. If no class is given,
device based is
assumed.
3) filters loaded from default.pa or manually loaded filters are either
device based or
stream group based filters. Because they are loaded manually and without
an initial
stream associated with them they should not be unloaded by module-filter
apply.
4) When using the filter.apply property we need further properties to
define the class
of the filter (device/group/stream) and the initial parameters. If it is
a group based filter,
a group name/number must also be supplied to distinguish between
multiple instances
of the same filter.
Have we forgotten anything? Any other comments on this approach?
Regards
Georg
