algesten · algesten · Nov 24, 2025 · Dec 11, 2025 · Dec 12, 2025 · Dec 16, 2025
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -1,5 +1,6 @@
 # Unreleased
 
+  * RTT as Duration #756
   * Network emulation for tests #774
   * Apple Crypto backend #763
   * Move all crypto backends out of main crate #768

diff --git a/Cargo.lock b/Cargo.lock
diff --git a/Cargo.toml b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "str0m"
-version = "0.13.0"
+version = "0.14.0"
 authors = ["Martin Algesten <martin@algesten.se>", "Hugo Tunius <h@tunius.se>", "Davide Bertola <dade@dadeb.it>"]
 description = "WebRTC library in Sans-IO style"
 license = "MIT OR Apache-2.0"

diff --git a/crypto/wincrypto/Cargo.toml b/crypto/wincrypto/Cargo.toml
@@ -22,4 +22,4 @@ windows = { version = "0.58", features = [
 ] }
 
 [dev-dependencies]
-str0m = { version = "0.12.0", path = "../../" }
+str0m = { version = "0.13.0", path = "../../" }
diff --git a/docs/SDP.md b/docs/SDP.md
@@ -116,5 +116,61 @@ by str0m or the client. For media str0m creates, it refuses to allow the client
 transition `Inactive` -> `RecvOnly`. All other transitions are fine, i.e. a client can change, also a
 str0m created media, from `Inactive` to `SendRecv`.
 
+## BUNDLE and Bundle Policies
+
+str0m only supports a single ICE transport, meaning all m-lines must
+be bundled together. The `a=group:BUNDLE` attribute in the SDP lists
+which m-lines share transport.
+
+### max-bundle vs max-compat
+
+[RFC 8843][rfc8843] defines bundle policies that control how ports are set in SDP offers:
+
+- **max-bundle**: Only the first m-line in the bundle has a real port
+  (typically 9). Subsequent bundled m-lines use `port=0` to indicate
+  they share transport with the first m-line.
+- **max-compat**: All m-lines use a non-zero port (typically 9), for
+    backwards compatibility with endpoints that don't understand
+    BUNDLE.
+
+The bundle policy is a local choice made by the offerer and is **not
+explicitly stated** in the SDP. It can only be inferred by looking at
+the port values on bundled m-lines.
+
+Example max-bundle offer:
+
+```
+a=group:BUNDLE 0 1
+m=audio 9 UDP/TLS/RTP/SAVPF 111   <- port 9
+m=video 0 UDP/TLS/RTP/SAVPF 96   <- port 0 (bundled, NOT rejected)
+```
+
+Example max-compat offer:
+
+```
+a=group:BUNDLE 0 1
+m=audio 9 UDP/TLS/RTP/SAVPF 111   <- port 9
+m=video 9 UDP/TLS/RTP/SAVPF 96   <- port 9
+```
+
+### How str0m handles this
+
+**Generating SDPs**: str0m produces max-compat style SDPs. All active
+m-lines use port 9. Only truly rejected m-lines (e.g., no codec
+match) use port 0.
+
+**Receiving SDPs**: str0m accepts both styles. An m-line with `port=0`
+is only considered rejected if it is NOT listed in the
+`a=group:BUNDLE` attribute. If it is in the BUNDLE group, `port=0`
+simply indicates the m-line shares transport with the first bundled
+m-line (max-bundle style).
+
+| Port | In BUNDLE group | Meaning                                 |
+|------|-----------------|-----------------------------------------|
+| 0    | Yes             | Valid bundled m-line (max-bundle style) |
+| 0    | No              | Rejected m-line                         |
+| 9    | Yes             | Valid bundled m-line (max-compat style) |
+
 [quote]: https://mailarchive.ietf.org/arch/msg/mmusic/2N1_-eUTVrmciX3LpSjkjFH7oCU/
 [sdpspec]: https://datatracker.ietf.org/doc/html/rfc3264#section-6.1
+[rfc8843]: https://datatracker.ietf.org/doc/html/rfc8843
diff --git a/src/change/sdp.rs b/src/change/sdp.rs
@@ -796,9 +796,10 @@ fn apply_offer(session: &mut Session, offer: SdpOffer) -> Result<(), RtcError> {
 
     update_session(session, &offer);
 
+    let bundle_mids = offer.bundle_mids();
     let new_lines = sync_medias(session, &offer).map_err(RtcError::RemoteSdp)?;
 
-    add_new_lines(session, &new_lines, true).map_err(RtcError::RemoteSdp)?;
+    add_new_lines(session, &new_lines, true, bundle_mids).map_err(RtcError::RemoteSdp)?;
 
     ensure_stream_tx(session);
 
@@ -814,14 +815,15 @@ fn apply_answer(
 
     update_session(session, &answer);
 
+    let bundle_mids = answer.bundle_mids();
     let new_lines = sync_medias(session, &answer).map_err(RtcError::RemoteSdp)?;
 
     // The new_lines from the answer must correspond to what we sent in the offer.
     if let Some(err) = pending.ensure_correct_answer(&new_lines) {
         return Err(RtcError::RemoteSdp(err));
     }
 
-    add_new_lines(session, &new_lines, false).map_err(RtcError::RemoteSdp)?;
+    add_new_lines(session, &new_lines, false, bundle_mids).map_err(RtcError::RemoteSdp)?;
 
     // Add all pending changes (since we pre-allocated SSRC communicated in the Offer).
     add_pending_changes(session, pending);
@@ -934,6 +936,7 @@ fn add_pending_changes(session: &mut Session, pending: Changes) {
 /// * New m-lines are returned to the caller.
 fn sync_medias<'a>(session: &mut Session, sdp: &'a Sdp) -> Result<Vec<&'a MediaLine>, String> {
     let mut new_lines = Vec::with_capacity(sdp.media_lines.len());
+    let bundle_mids = sdp.bundle_mids();
 
     for (idx, m) in sdp.media_lines.iter().enumerate() {
         // First, match existing m-lines.
@@ -958,6 +961,7 @@ fn sync_medias<'a>(session: &mut Session, sdp: &'a Sdp) -> Result<Vec<&'a MediaL
                         &session.codec_config,
                         &session.exts,
                         &mut session.streams,
+                        bundle_mids,
                     );
 
                     continue;
@@ -984,6 +988,7 @@ fn add_new_lines(
     session: &mut Session,
     new_lines: &[&MediaLine],
     is_offer: bool,
+    bundle_mids: Option<&[Mid]>,
 ) -> Result<(), String> {
     for m in new_lines {
         let idx = session.line_count();
@@ -993,7 +998,12 @@ fn add_new_lines(
 
             // For disabled (rejected) m-lines, don't fire open event
             // and the direction will be set to Inactive by update_media.
-            media.need_open_event = is_offer && !m.disabled;
+            // In max-bundle, port=0 with the MID in BUNDLE group is NOT rejected.
+            let is_in_bundle = bundle_mids
+                .map(|mids| mids.contains(&m.mid()))
+                .unwrap_or(false);
+            let is_rejected = m.disabled && !is_in_bundle;
+            media.need_open_event = is_offer && !is_rejected;
 
             // Match/remap remote params.
             session
@@ -1009,6 +1019,7 @@ fn add_new_lines(
                 &session.codec_config,
                 &session.exts,
                 &mut session.streams,
+                bundle_mids,
             );
 
             session.add_media(media);
@@ -1067,13 +1078,23 @@ fn update_media(
     config: &CodecConfig,
     exts: &ExtensionMap,
     streams: &mut Streams,
+    bundle_mids: Option<&[Mid]>,
 ) {
-    // If the m-line is disabled (port=0), clear remote_pts and set direction to Inactive.
-    // This handles the case where the remote rejects an m-line.
-    if m.disabled {
+    // If the m-line has port=0, it could mean:
+    // 1. The m-line is rejected (not in BUNDLE group)
+    // 2. The m-line is bundled with another m-line (max-bundle format, RFC 8843)
+    //
+    // In max-bundle, secondary m-lines use port=0 to indicate they share transport
+    // with the first m-line. This is NOT a rejection.
+    let is_in_bundle = bundle_mids
+        .map(|mids| mids.contains(&m.mid()))
+        .unwrap_or(false);
+    let is_rejected = m.disabled && !is_in_bundle;
+
+    if is_rejected {
         if !media.disabled() {
             debug!(
-                "Mid ({}) is rejected (port=0), setting to Inactive",
+                "Mid ({}) is rejected (port=0, not in BUNDLE), setting to Inactive",
                 media.mid()
             );
         }
@@ -1603,7 +1624,7 @@ mod test {
     use sdp::SimulcastLayer as SdpSimulcastLayer;
 
     use crate::format::Codec;
-    use crate::media::Simulcast;
+    use crate::media::{Simulcast, SimulcastLayer};
     use crate::sdp::RtpMap;
 
     use super::*;
@@ -1755,11 +1776,11 @@ mod test {
 
         let mut rtc1 = Rtc::new();
 
-        let simulcast = Simulcast::builder()
-            .add_send_layer("h")
-            .add_send_layer("m")
-            .add_send_layer("l")
-            .build();
+        let mut simulcast = Simulcast::new();
+
+        simulcast.add_send_layer(SimulcastLayer::new("h"));
+        simulcast.add_send_layer(SimulcastLayer::new("m"));
+        simulcast.add_send_layer(SimulcastLayer::new("l"));
 
         let mut change = rtc1.sdp_api();
         change.add_media(
@@ -1843,42 +1864,49 @@ mod test {
 
         let mut rtc1 = Rtc::new();
 
-        let simulcast_builder = Simulcast::builder()
-            // High layer
-            .add_send_layer_with_attributes("high")
-            .max_width(1280)
-            .max_height(720)
-            .max_br(1100000)
-            .max_br(1300000)
-            .max_br(1500000) // the last one wins
-            .max_fps(30)
-            .finish()
-            // Medium layer
-            .add_send_layer_with_attributes("medium")
-            .max_width(640)
-            .max_height(360)
-            .max_br(600000)
-            // No max_fps
-            .finish()
-            // Low layer
-            .add_send_layer_with_attributes("low")
-            // No max_width
-            .max_height(180)
-            .max_br(200000)
-            .max_fps(15)
-            .finish()
-            // Custom attribute
-            .add_send_layer_with_attributes("custom")
-            .custom("foo", "bar")
-            .finish();
-
-        // Make sure we can add layers one at a time, e.g. in a loop in a user's application
-        let simulcast = simulcast_builder
-            // No attributes
-            .add_send_layer_with_attributes("no_attrs")
-            .finish()
-            // Build the simulcast itself
-            .build();
+        let mut simulcast = Simulcast::new();
+
+        // High layer
+        simulcast.add_send_layer(
+            SimulcastLayer::new_with_attributes("high")
+                .max_width(1280)
+                .max_height(720)
+                .max_br(1100000)
+                .max_br(1300000)
+                .max_br(1500000) // the last one wins
+                .max_fps(30)
+                .build(),
+        );
+
+        // Medium layer
+        simulcast.add_send_layer(
+            SimulcastLayer::new_with_attributes("medium")
+                .max_width(640)
+                .max_height(360)
+                .max_br(600000)
+                // No max_fps
+                .build(),
+        );
+
+        // Low layer
+        simulcast.add_send_layer(
+            SimulcastLayer::new_with_attributes("low")
+                // No max_width
+                .max_height(180)
+                .max_br(200000)
+                .max_fps(15)
+                .build(),
+        );
+
+        // Custom attribute
+        simulcast.add_send_layer(
+            SimulcastLayer::new_with_attributes("custom")
+                .custom("foo", "bar")
+                .build(),
+        );
+
+        // No attributes
+        simulcast.add_send_layer(SimulcastLayer::new_with_attributes("no_attrs").build());
 
         let mut change = rtc1.sdp_api();
         change.add_media(