[gst-devel] How to deal with multiple dynamic sources?

[Henk Kok]

Hi, all,

For a project we are doing, we need a filter graph that has multiple 
audio sources, which can be selected or which can be mixed. The sources 
are not necessarilly all active. To get a feeling of how to do this with 
gstreamer, I have been toying around a bit, but so far I have not been 
able to get it to do what I want it to do.

In my test application, I have two file sources with mad-decoders, which 
connect through a convertor and volume controle, to an adder. The adder 
connects to another volume control, and that connects to the sink.

When I change the state to playing, this works. However, pausing goes 
horribly wrong. There have been situations in which everything blocks if 
I pause only one of the two playbacks, or a situation where both 
playbacks simply continue when the state changes to paused. I have made 
a modification to the architecture, which now looks like this:

+--------------------------------------------------------------------------------------------------+
|                                   
PIPELINE                                                       |
| 
+---------------------------------------------------+                                            
|
| |                BIN[0]                             
|                                            |
| |+---------+  +---------+  +---------+  +---------+ 
|                                            |
| || filesrc |->| decoder |->|  conv   |->| volume  
|-+-+                                          |
| |+---------+  +---------+  +---------+  +---------+ | |  +---------+  
+---------+  +---------+   |
| +---------------------------------------------------+ +->|         |  
|         |  |         |   |
|                                                          |  ADDER  
|->|  VOLUME |->|  SINK   |   |
| +---------------------------------------------------+ +->|         |  
|         |  |         |   |
| |                BIN[1]                             | |  +---------+  
+---------+  +---------+   |
| |+---------+  +---------+  +---------+  +---------+ | 
|                                          |
| || filesrc |->| decoder |->|  conv   |->| volume  
|-+-+                                          |
| |+---------+  +---------+  +---------+  +---------+ 
|                                            |
| 
+---------------------------------------------------+                                            
|
+--------------------------------------------------------------------------------------------------+

The 'BIN's are also pipelines, btw, at the moment running their own main 
loop. Also in this situation, when I set the state of a BIN to paused, 
that branch will keep playing. When I set it to ready, it does stop, but 
blocks (probably on the adder) the playback of the other branch. 
Disconnecting the BIN from the adder (and cleaning up the pad that was 
created when connecting) lifts that problem. But then, when I want to 
resume playback of the "paused" branch, it will start playing from the 
wrong location. It will start playing from the time 'current time minus 
time we paused'. I have been trying to lift that particular problem with 
gst_element_set_base_time, (on about any element in the BIN and the BIN 
itself)  but that doesn't seem to make any difference.

I have also considered of putting the adder, volume and sink in Yet 
Another Pipeline, but then that pipeline must have a dynamic number of 
sink pads and I am not entirely sure how to handle this. I also doubt it 
would help much.

Another question: is there a means of fading out before going to paused, 
and fading in after going to playing? I would like to prevent plops from 
occuring. The only option I see for this at the moment, is to modify the 
volume element for this.

I have zillions of other questions, but for now, let's leave it at this. :-)

Hope someone can help me out here,

Best regards,

- Henk.