streaming

commit 61bd1078782b91e755baeb63e85097ceab5aa2c4
parent 10c716ceab2f4541c398aa228af294a6eeff9edc
Author: Oliver Lowe <o@olowe.co>
Date:   Fri,  2 Aug 2024 21:22:28 +1000

cmd/autx: correctly copy bytes out to the network

We weren't really copying them before, we were just grabbing whatever
we had in our buffer which was constantly being overwritten!

This patch also correctly specifies and sets the payload size to
always fits a UDP packet to fit in the typical network MTU of 1400-ish
bytes. The sample rate and transmission interval are modified
accordingly with guidance from RFC 3551.

Diffstat:
M
cmd/autx/autx.go
 | 
52
++++++++++++++++++++++++++++++++++++++--------------

1 file changed, 38 insertions(+), 14 deletions(-)
diff --git a/cmd/autx/autx.go b/cmd/autx/autx.go
@@ -1,9 +1,9 @@
 // Command autx transmits audio over the network via RTP.
 // It reads raw audio from the standard input
-// and transmits it to the provided address.
+// and transmits it to the provided address every 30 milliseconds.
 // Audio must be single-channel (mono),
 // signed 16-bit linear PCM data in big-endian byte order.
-// The sample rate must be 44.1KHz.
+// The sample rate must be 22.05KHz.
 //
 // Its usage is:
 //
@@ -24,16 +24,19 @@ import (
 	"fmt"
 	"io"
 	"log"
+	"net"
 	"os"
+	"strconv"
+	"strings"
 	"time"
 
 	"github.com/untangledco/streaming/rtp"
 	"github.com/untangledco/streaming/sdp"
 )
 
-const sampleRate = 4000
-const bitsPerSample = 8
-const tick = 500 // milliseconds
+const sampleRate = 22050
+const bitsPerSample = 16
+const tick = 30 // milliseconds
 const packetInterval = tick * time.Millisecond
 const bufSize = sampleRate * bitsPerSample / 8 / 1000 * tick
 
@@ -51,24 +54,41 @@ func main() {
 	}
 	session.Clock = 44100 // 44.1KHz, not the audio sample rate.
 
+	ipv := "IP4"
+	origin := "127.0.0.1"
+	if strings.HasPrefix(os.Args[1], "[") {
+		ipv = "IP6"
+		origin = "::1"
+	}
+	_, port, err := net.SplitHostPort(os.Args[1])
+	if err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+	nport, err := strconv.Atoi(port)
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "parse port:", err)
+		os.Exit(1)
+	}
+
 	description := sdp.Session{
 		Origin: sdp.Origin{
 			Username:    sdp.NoUsername,
 			ID:          sdp.Now(),
 			Version:     sdp.Now(),
-			AddressType: "IP6",
-			Address:     "::1",
+			AddressType: ipv,
+			Address:     origin,
 		},
 		Name: "test",
 		Media: []sdp.Media{
 			{
 				Type:      sdp.MediaTypeAudio,
-				Port:      9999,
+				Port:      nport,
 				Transport: sdp.ProtoRTP,
-				Format:    []string{fmt.Sprintf("%d", rtp.PayloadType(99))},
+				Format:    []string{fmt.Sprintf("%d", rtp.PayloadType(11))},
 				Attributes: []string{
-					fmt.Sprintf("rtpmap:%d", rtp.PayloadType(99)),
-					fmt.Sprintf("L8/%d", sampleRate),
+					fmt.Sprintf("rtpmap:%d", rtp.PayloadType(11)),
+					fmt.Sprintf("L16/%d", sampleRate),
 				},
 			},
 		},
@@ -80,7 +100,7 @@ func main() {
 		buf := &bytes.Buffer{}
 		p := rtp.Packet{
 			Header: rtp.Header{
-				Type: rtp.PayloadL16,
+				Type: rtp.PayloadType(11),
 			},
 		}
 		for {
@@ -94,12 +114,16 @@ func main() {
 			} else if err != nil {
 				log.Println(err)
 			}
-			p.Payload = buf.Bytes()
+			p.Payload = bytes.Clone(buf.Bytes())
 			out <- p
 		}
 	}()
 
-	for p := range out {
+	for range time.NewTicker(packetInterval).C {
+		p, ok := <-out
+		if !ok {
+			return
+		}
 		if err := session.Transmit(&p); err != nil {
 			log.Println(err)
 		}