Add simulcast sending support

examples/chat.rs

@@ -495,8 +495,13 @@ impl Client {
             if let TrackOutState::ToOpen = track.state {
                 if let Some(track_in) = track.track_in.upgrade() {
                     let stream_id = track_in.origin.to_string();
-                    let mid =
-                        change.add_media(track_in.kind, Direction::SendOnly, Some(stream_id), None);
+                    let mid = change.add_media(
+                        track_in.kind,
+                        Direction::SendOnly,
+                        Some(stream_id),
+                        None,
+                        None,
+                    );
                     track.state = TrackOutState::Negotiating(mid);
                 }
             }

src/change/direct.rs

@@ -232,14 +232,19 @@ impl<'a> DirectApi<'a> {
         mid: Mid,
         rid: Option<Rid>,
     ) -> &mut StreamTx {
-        let Some(media) = self.rtc.session.media_by_mid(mid) else {
+        let Some(media) = self.rtc.session.media_by_mid_mut(mid) else {
             panic!("No media declared for mid: {}", mid);
         };
 
         let is_audio = media.kind().is_audio();
 
         let midrid = MidRid(mid, rid);
 
+        // If there is a RID tx, declare it so we an use it in Writer API
+        if let Some(rid) = rid {
+            media.add_to_rid_tx(rid);
+        }
+
         let stream = self
             .rtc
             .session

src/change/sdp.rs

@@ -8,7 +8,7 @@ use crate::crypto::Fingerprint;
 use crate::format::CodecConfig;
 use crate::format::PayloadParams;
 use crate::io::Id;
-use crate::media::Media;
+use crate::media::{Media, Simulcast};
 use crate::packet::MediaKind;
 use crate::rtp_::MidRid;
 use crate::rtp_::Rid;
@@ -128,7 +128,7 @@ impl<'a> SdpApi<'a> {
     /// let mut rtc = Rtc::new();
     ///
     /// let mut changes = rtc.sdp_api();
-    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None);
+    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None, None);
     /// let (offer, pending) = changes.apply().unwrap();
     ///
     /// // send offer to remote peer, receive answer back
@@ -201,7 +201,7 @@ impl<'a> SdpApi<'a> {
     /// let mut changes = rtc.sdp_api();
     /// assert!(!changes.has_changes());
     ///
-    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendRecv, None, None);
+    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendRecv, None, None, None);
     /// assert!(changes.has_changes());
     /// # }
     /// ```
@@ -227,7 +227,7 @@ impl<'a> SdpApi<'a> {
     ///
     /// let mut changes = rtc.sdp_api();
     ///
-    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendRecv, None, None);
+    /// let mid = changes.add_media(MediaKind::Audio, Direction::SendRecv, None, None, None);
     /// # }
     /// ```
     pub fn add_media(
@@ -236,6 +236,7 @@ impl<'a> SdpApi<'a> {
         dir: Direction,
         stream_id: Option<String>,
         track_id: Option<String>,
+        simulcast: Option<crate::media::Simulcast>,
     ) -> Mid {
         let mid = self.rtc.new_mid();
 
@@ -266,8 +267,15 @@ impl<'a> SdpApi<'a> {
             Id::<20>::random().to_string()
         };
 
-        let rtx = kind.is_video().then(|| self.rtc.session.streams.new_ssrc());
-        let ssrcs = vec![(self.rtc.session.streams.new_ssrc(), rtx)];
+        let mut ssrcs = Vec::new();
+
+        // Main SSRC, not counting RTX.
+        let main_ssrc_count = simulcast.as_ref().map(|s| s.send.len()).unwrap_or(1);
+
+        for _ in 0..main_ssrc_count {
+            let rtx = kind.is_video().then(|| self.rtc.session.streams.new_ssrc());
+            ssrcs.push((self.rtc.session.streams.new_ssrc(), rtx));
+        }
 
         // TODO: let user configure stream/track name.
         let msid = Msid {
@@ -282,6 +290,7 @@ impl<'a> SdpApi<'a> {
             kind,
             dir,
             ssrcs,
+            simulcast,
 
             // Added later
             pts: vec![],
@@ -459,11 +468,11 @@ impl<'a> SdpApi<'a> {
     /// # use str0m::Rtc;
     /// let mut rtc = Rtc::new();
     /// let mut changes = rtc.sdp_api();
-    /// changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None);
+    /// changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None, None);
     /// let (_offer, pending) = changes.apply().unwrap();
     ///
     /// let mut changes = rtc.sdp_api();
-    /// changes.add_media(MediaKind::Video, Direction::SendOnly, None, None);
+    /// changes.add_media(MediaKind::Video, Direction::SendOnly, None, None, None);
     /// changes.merge(pending);
     ///
     /// // This `SdpOffer` will have changes from the first `SdpPendingChanges`
@@ -489,7 +498,7 @@ impl<'a> SdpApi<'a> {
 /// let mut rtc = Rtc::new();
 ///
 /// let mut changes = rtc.sdp_api();
-/// let mid = changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None);
+/// let mid = changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None, None);
 /// let (offer, pending) = changes.apply().unwrap();
 ///
 /// // send offer to remote peer, receive answer back
@@ -561,6 +570,7 @@ pub(crate) struct AddMedia {
     pub kind: MediaKind,
     pub dir: Direction,
     pub ssrcs: Vec<(Ssrc, Option<Ssrc>)>,
+    pub simulcast: Option<Simulcast>,
 
     // pts and index are filled in when creating the SDP OFFER.
     // The default PT order is set by the Session (BUNDLE).
@@ -894,9 +904,12 @@ fn add_pending_changes(session: &mut Session, pending: Changes) {
         media.set_cname(add_media.cname);
         media.set_msid(add_media.msid);
 
-        for (ssrc, rtx) in add_media.ssrcs {
-            // TODO: When we allow sending RID, we need to add that here.
-            let midrid = MidRid(add_media.mid, None);
+        // If there are RIDs, the SSRC order matches that of the rid order.
+        let rids = add_media.simulcast.map(|x| x.send).unwrap_or(vec![]);
+
+        for (i, (ssrc, rtx)) in add_media.ssrcs.into_iter().enumerate() {
+            let maybe_rid = rids.get(i).cloned();
+            let midrid = MidRid(add_media.mid, maybe_rid);
 
             let stream = session.streams.declare_stream_tx(ssrc, rtx, midrid);
 
@@ -1068,8 +1081,14 @@ fn update_media(
         media.set_direction(new_dir);
     }
 
-    for rid in m.rids().iter() {
-        media.expect_rid(*rid);
+    if new_dir.is_sending() {
+        // The other side has declared how it EXPECTING to receive. We must only send
+        // the RIDs declared in the answer.
+        media.set_rid_tx(m.rids().into());
+    }
+    if new_dir.is_receiving() {
+        // The other side has declared what it proposes to send. We are accepting it.
+        media.set_rid_rx(m.rids().into());
     }
 
     // Narrowing/ordering of of PT
@@ -1102,44 +1121,47 @@ fn update_media(
     }
     media.set_remote_extmap(remote_extmap);
 
-    if new_dir.is_receiving() {
-        // SSRC changes
-        // This will always be for ReceiverSource since any incoming a=ssrc line will be
-        // about the remote side's SSRC.
-        let infos = m.ssrc_info();
-        let main = infos.iter().filter(|i| i.repairs.is_none());
-
-        if m.simulcast().is_none() {
-            // Only use pre-communicated SSRC if we are running without simulcast.
-            // We found a bug in FF where the order of the simulcast lines does not
-            // correspond to the order of the simulcast declarations. In this case
-            // it's better to fall back on mid/rid dynamic mapping.
-
-            for i in main {
-                // TODO: If the remote is communicating _BOTH_ rid and a=ssrc this will fail.
-                info!("Adding pre-communicated SSRC: {:?}", i);
-                let repair_ssrc = infos
-                    .iter()
-                    .find(|r| r.repairs == Some(i.ssrc))
-                    .map(|r| r.ssrc);
-
-                // If remote communicated a main a=ssrc, but no RTX, we will not send nacks.
-                let midrid = MidRid(media.mid(), None);
-                let suppress_nack = repair_ssrc.is_none();
-                streams.expect_stream_rx(i.ssrc, repair_ssrc, midrid, suppress_nack);
-            }
-        }
+    // SSRC changes
+    // This will always be for ReceiverSource since any incoming a=ssrc line will be
+    // about the remote side's SSRC.
+    if !new_dir.is_receiving() {
+        return;
+    }
 
-        // Simulcast configuration
-        if let Some(s) = m.simulcast() {
-            if s.is_munged {
-                warn!("Not supporting simulcast via munging SDP");
-            } else if media.simulcast().is_none() {
-                // Invert before setting, since it has a recv and send config.
-                media.set_simulcast(s.invert());
-            }
+    // Simulcast configuration
+    if let Some(s) = m.simulcast() {
+        if s.is_munged {
+            warn!("Not supporting simulcast via munging SDP");
+        } else if media.simulcast().is_none() {
+            // Invert before setting, since it has a recv and send config.
+            media.set_simulcast(s.invert());
         }
     }
+
+    // Only use pre-communicated SSRC if we are running without simulcast.
+    // We found a bug in FF where the order of the simulcast lines does not
+    // correspond to the order of the simulcast declarations. In this case
+    // it's better to fall back on mid/rid dynamic mapping.
+    if m.simulcast().is_some() {
+        return;
+    }
+
+    let infos = m.ssrc_info();
+    let main = infos.iter().filter(|i| i.repairs.is_none());
+
+    for i in main {
+        // TODO: If the remote is communicating _BOTH_ rid and a=ssrc this will fail.
+        info!("Adding pre-communicated SSRC: {:?}", i);
+        let repair_ssrc = infos
+            .iter()
+            .find(|r| r.repairs == Some(i.ssrc))
+            .map(|r| r.ssrc);
+
+        // If remote communicated a main a=ssrc, but no RTX, we will not send nacks.
+        let midrid = MidRid(media.mid(), None);
+        let suppress_nack = repair_ssrc.is_none();
+        streams.expect_stream_rx(i.ssrc, repair_ssrc, midrid, suppress_nack);
+    }
 }
 
 trait AsSdpMediaLine {
@@ -1291,18 +1313,13 @@ impl AsSdpMediaLine for Media {
             }
         }
 
-        let count = ssrcs_tx.len();
-        #[allow(clippy::comparison_chain)]
-        if count == 1 {
-            let (ssrc, ssrc_rtx) = &ssrcs_tx[0];
+        for (ssrc, ssrc_rtx) in ssrcs_tx {
             if let Some(ssrc_rtx) = ssrc_rtx {
                 attrs.push(MediaAttribute::SsrcGroup {
                     semantics: "FID".to_string(),
                     ssrcs: vec![*ssrc, *ssrc_rtx],
                 });
             }
-        } else {
-            // TODO: handle simulcast
         }
 
         MediaLine {
@@ -1549,7 +1566,10 @@ impl Change {
 
 #[cfg(test)]
 mod test {
+    use sdp::RestrictionId;
+
     use crate::format::Codec;
+    use crate::media::Simulcast;
     use crate::sdp::RtpMap;
 
     use super::*;
@@ -1595,11 +1615,11 @@ mod test {
 
         let mut rtc = Rtc::new();
         let mut changes = rtc.sdp_api();
-        changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None);
+        changes.add_media(MediaKind::Audio, Direction::SendOnly, None, None, None);
         let (offer, pending) = changes.apply().unwrap();
 
         let mut changes = rtc.sdp_api();
-        changes.add_media(MediaKind::Video, Direction::SendOnly, None, None);
+        changes.add_media(MediaKind::Video, Direction::SendOnly, None, None, None);
         changes.merge(pending);
         let (new_offer, _) = changes.apply().unwrap();
 
@@ -1624,7 +1644,7 @@ mod test {
             .build();
 
         let mut change1 = rtc1.sdp_api();
-        change1.add_media(MediaKind::Video, Direction::SendOnly, None, None);
+        change1.add_media(MediaKind::Video, Direction::SendOnly, None, None, None);
         let (offer1, _) = change1.apply().unwrap();
 
         let answer = rtc2.sdp_api().accept_offer(offer1).unwrap();
@@ -1652,4 +1672,73 @@ mod test {
             "VP9 was not offered, so it should not be present in the answer"
         );
     }
+
+    #[test]
+    fn simulcast_ssrc_allocation() {
+        crate::init_crypto_default();
+
+        let mut rtc1 = Rtc::new();
+
+        let mut change = rtc1.sdp_api();
+        change.add_media(
+            MediaKind::Video,
+            Direction::SendOnly,
+            None,
+            None,
+            Some(Simulcast {
+                send: vec!["m".into(), "h".into(), "l".into()],
+                recv: vec![],
+            }),
+        );
+
+        let Change::AddMedia(am) = &change.changes[0] else {
+            panic!("Not AddMedia?!");
+        };
+
+        // these should be organized in order: m, h, l
+        let pending_ssrcs = am.ssrcs.clone();
+        assert_eq!(pending_ssrcs.len(), 3);
+
+        for p in &pending_ssrcs {
+            assert!(p.1.is_some()); // all should have rtx
+        }
+
+        let (offer, _) = change.apply().unwrap();
+        let sdp = offer.into_inner();
+        let line = &sdp.media_lines[0];
+
+        assert_eq!(
+            line.simulcast().unwrap().send,
+            SimulcastGroups(vec![
+                RestrictionId("m".into(), true),
+                RestrictionId("h".into(), true),
+                RestrictionId("l".into(), true),
+            ])
+        );
+
+        // Each SSRC, both regular and RTX get their own a=ssrc line.
+        assert_eq!(line.ssrc_info().len(), pending_ssrcs.len() * 2);
+
+        let fids: Vec<_> = line
+            .attrs
+            .iter()
+            .filter_map(|a| {
+                if let MediaAttribute::SsrcGroup { semantics, ssrcs } = a {
+                    // We don't have any other semantics right now.
+                    assert_eq!(semantics, "FID");
+                    assert_eq!(ssrcs.len(), 2);
+                    Some((ssrcs[0], ssrcs[1]))
+                } else {
+                    None
+                }
+            })
+            .collect();
+
+        assert_eq!(fids.len(), pending_ssrcs.len());
+
+        for (a, b) in fids.iter().zip(pending_ssrcs.iter()) {
+            assert_eq!(a.0, b.0);
+            assert_eq!(Some(a.1), b.1);
+        }
+    }
 }