fmp4: Return a running time in get_next_time()

We were currently returning a value based on the next chunk PTS, but the
expectation in GstAggregator is that we return a running time. This
resulted in spurious wakeups and warnings like:

0:00:01.501685123 1552995 0x55899715c1e0 WARN                 fmp4mux mux/fmp4/src/fmp4mux/imp.rs:1818:gstfmp4::fmp4mux::imp::FMP4Mux::drain_buffers:<fmp4mux0:sink_1> Don't have a complete GOP for the first stream on timeout in a live pipeline

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1127>

1 files changed, 16 insertions, 1 deletions

diff --git a/mux/fmp4/src/fmp4mux/imp.rs b/mux/fmp4/src/fmp4mux/imp.rs
index 08c39d1be..38e48dd07 100644
--- a/mux/fmp4/src/fmp4mux/imp.rs
+++ b/mux/fmp4/src/fmp4mux/imp.rs
@@ -2928,7 +2928,22 @@ impl ElementImpl for FMP4Mux {
 impl AggregatorImpl for FMP4Mux {
     fn next_time(&self) -> Option<gst::ClockTime> {
         let state = self.state.lock().unwrap();
-        state.chunk_start_pts.opt_add(state.timeout_delay)
+        let agg = self.obj();
+        let segment = agg
+            .src_pad()
+            .segment()
+            .downcast::<gst::ClockTime>()
+            .expect("TIME segment");
+
+        state
+            .chunk_start_pts
+            .opt_add(state.timeout_delay)
+            .and_then(|mut t| {
+                if !agg.class().as_ref().variant.is_single_stream() {
+                    t += SEGMENT_OFFSET;
+                }
+                segment.to_running_time(t)
+            })
     }
 
     fn sink_query(