Latency messages should be posted on pipeline modifications that change the latency.
Submitted by Olivier Crête
After discussion on bug 745197, it seems we have many use-cases where dynamic pipeline modifications result in changes to the latency, but nothing automatically posts the latency message. For example, when adding a new source to n->1 element (GstAggregator, input-selector, etc), in this case, the elements should probably send out a latency message on the first buffer on a new pad, as that means that a source was connected.
This gets a bit trickier for the cases when one replaces a source in a running pipeline, that may just require manually posting the latency message..
If we start posting more latency message, one possible optimization would be to drop the messages on top-level bins that are not in the playing state yet.
I wish we pushed down the latency as a stick event instead of a query..