Rework packet recovery in diskwriter.

We now request a keyframe if we lose too many packets.

diskwriter/diskwriter.go

@@ -410,26 +410,27 @@ func (t *diskTrack) Write(buf []byte) (int, error) {
 	if valid(t.lastSeqno) {
 		lastSeqno := uint16(value(t.lastSeqno))
 		if ((p.SequenceNumber - lastSeqno) & 0x8000) == 0 {
+			// jump forward
 			count := p.SequenceNumber - lastSeqno
-			if count > 0 && count < 128 {
-				for i := lastSeqno + 1; i != p.SequenceNumber; i++ {
-					// different buf each time
-					buf := make([]byte, 1504)
-					n := t.remote.GetPacket(i, buf, true)
-					if n == 0 {
-						continue
+			if count < 256 {
+				for i := uint16(1); i < count; i++ {
+					recover(t, lastSeqno + i)
 				}
-					p := new(rtp.Packet)
-					err := p.Unmarshal(buf)
-					if err == nil {
-						t.writeRTP(p)
+			} else {
+				requestKeyframe(t)
 			}
-				}
-			}
-		}
-	}
-
 			t.lastSeqno = some(uint32(p.SequenceNumber))
+		} else {
+			// jump backward
+			count := lastSeqno - p.SequenceNumber
+			if count >= 512 {
+				t.lastSeqno = none
+				requestKeyframe(t)
+			}
+		}
+	} else {
+		t.lastSeqno = some(uint32(p.SequenceNumber))
+	}
 
 	err = t.writeRTP(p)
 	if err != nil {
@@ -438,6 +439,29 @@ func (t *diskTrack) Write(buf []byte) (int, error) {
 	return len(buf), nil
 }
 
+func recover(t *diskTrack, seqno uint16) {
+	// since the samplebuilder retains packets, use a fresh buffer
+	buf := make([]byte, 1504)
+	n := t.remote.GetPacket(seqno, buf, true)
+	if n == 0 {
+		return
+	}
+	p := new(rtp.Packet)
+	err := p.Unmarshal(buf)
+	if err != nil {
+		return
+	}
+	t.writeRTP(p)
+}
+
+func requestKeyframe(t *diskTrack) {
+	now := time.Now()
+	if now.Sub(t.kfRequested) > 500*time.Millisecond {
+		t.remote.RequestKeyframe()
+		t.kfRequested = now
+	}
+}
+
 // writeRTP writes the packet without doing any loss recovery.
 // Called locked.
 func (t *diskTrack) writeRTP(p *rtp.Packet) error {
@@ -513,10 +537,7 @@ func (t *diskTrack) writeBuffered(force bool) error {
 		if keyframe {
 			t.lastKf = now
 		} else if t.writer == nil || now.Sub(t.lastKf) > 4*time.Second {
-			if now.Sub(t.kfRequested) > time.Second {
-				t.remote.RequestKeyframe()
-				t.kfRequested = now
-			}
+			requestKeyframe(t)
 			return nil
 		}