livesync: add support for variable framerate

A variable framerate is signaled by a framerate of 0/1 and the
max-framerate field. This may be the result of source that can produce
up to max-framerate frames, but may produce less. A live stream may
expect frames with the expected max-framerate and updated timestamps
even if the frame contents didn't change.

Support streams with variable framerate in livesync and send frames with
max-framerate to downstream.

utils/livesync/src/livesync/imp.rs

@@ -39,7 +39,12 @@ fn audio_info_from_caps(
 fn duration_from_caps(caps: &gst::CapsRef) -> Option<gst::ClockTime> {
     caps.structure(0)
         .filter(|s| s.name().starts_with("video/") || s.name().starts_with("image/"))
-        .and_then(|s| s.get::<gst::Fraction>("framerate").ok())
+        .and_then(|s| {
+            s.get::<gst::Fraction>("framerate")
+                .ok()
+                .filter(|f| f.denom() != 1 || f.numer() != 0)
+                .or_else(|| s.get::<gst::Fraction>("max-framerate").ok())
+        })
         .filter(|framerate| framerate.denom() > 0 && framerate.numer() > 0)
         .and_then(|framerate| {
             gst::ClockTime::SECOND.mul_div_round(framerate.denom() as u64, framerate.numer() as u64)

utils/livesync/tests/livesync.rs

@@ -120,6 +120,32 @@ fn test_video_negotiate_framerate_fixed() {
     assert_eq!(current_caps, src_caps);
 }
 
+#[test]
+fn test_video_negotiate_framerate_variable() {
+    init();
+
+    let mut h = gst_check::Harness::new("livesync");
+
+    let src_caps = gst::Caps::builder("video/x-raw")
+        .field("framerate", gst::Fraction::new(0, 1))
+        .field("max-framerate", gst::Fraction::new(30, 1))
+        .build();
+    h.set_src_caps(src_caps.clone());
+
+    h.play();
+
+    let buffer = gst::Buffer::new();
+    assert!(h.push_and_pull(buffer).is_ok());
+
+    let current_caps = h
+        .sinkpad()
+        .expect("harness has no sinkpad")
+        .current_caps()
+        .expect("current caps missing");
+
+    assert_eq!(current_caps, src_caps);
+}
+
 fn test_video(singlesegment: bool) {
     init();