From 871756bb70350e4a69d6b66c7883259cd5943ab9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sebastian=20Dr=C3=B6ge?= <sebastian@centricular.com>
Date: Thu, 22 Aug 2024 18:57:45 +0300
Subject: [PATCH] ndisrc: Reset timestamp tracking if remote time goes
 backwards

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1727>
---
 net/ndi/src/ndisrc/imp.rs | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/net/ndi/src/ndisrc/imp.rs b/net/ndi/src/ndisrc/imp.rs
index 7da3761c..af0a8b1c 100644
--- a/net/ndi/src/ndisrc/imp.rs
+++ b/net/ndi/src/ndisrc/imp.rs
@@ -1065,7 +1065,25 @@ impl Observations {
             };
 
         let local_diff = local_time.saturating_sub(base_local_time);
-        let remote_diff = remote_time.saturating_sub(base_remote_time);
+        let Some(remote_diff) = remote_time.checked_sub(base_remote_time) else {
+            gst::warning!(CAT, obj = element, "Backwards remote time, resetting",);
+
+            let discont = !self.deltas.is_empty();
+
+            gst::debug!(
+                CAT,
+                obj = element,
+                "Initializing base time: local {}, remote {}",
+                local_time,
+                remote_time,
+            );
+
+            self.reset();
+            self.base_local_time = Some(local_time);
+            self.base_remote_time = Some(remote_time);
+
+            return Some((local_time, duration, discont));
+        };
         let delta = (local_diff.nseconds() as i64) - (remote_diff.nseconds() as i64);
         let slope = local_diff.nseconds() as f64 / remote_diff.nseconds() as f64;