Implemented precise metadata and timing information packet stream

README.md

@@ -16,9 +16,7 @@ Radio streamer ([kawa](https://github.com/Luminarys/kawa) drop-in compatible).
 * Supports extra encoder bitrate control settings (CBR, VBR, auto, etc.)
 * Can read and apply ReplayGain tags, or normalize audio loudness.
 * Can have audio sources over HTTP(s) URLs on `path` property, and supports seeking.
-
-# Future improvements
-* Implement precise timing information side-channel
+* Precise metadata and timing information packet stream, trigger via `x-audio-packet-stream: 1` HTTP header.
 
 ## Dependencies
 ### Go >= 1.18

queue.go

@@ -1,6 +1,9 @@
 package main
 
 import (
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"git.gammaspectra.live/S.O.N.G/Kirika/audio"
@@ -386,6 +389,50 @@ func (q *Queue) GetListeners() (listeners []*ListenerInformation) {
 	return
 }
 
+type packetStreamType uint64
+
+const (
+	Header = packetStreamType(iota)
+	DataKeepLast
+	DataKeep
+	DataGroupKeep
+	DataGroupDiscard
+	DataDiscard
+	TrackIdentifier
+	TrackMetadata
+)
+
+type packetStreamFrame struct {
+	Type              packetStreamType
+	StartSampleNumber int64
+	DurationInSamples int64
+	//automatically filled based on Data
+	//Size              uint64
+	Data []byte
+}
+
+func (p *packetStreamFrame) Encode() []byte {
+	buf := new(bytes.Buffer)
+
+	varBuf := make([]byte, binary.MaxVarintLen64)
+
+	n := binary.PutUvarint(varBuf, uint64(p.Type))
+	buf.Write(varBuf[:n])
+
+	n = binary.PutVarint(varBuf, p.StartSampleNumber)
+	buf.Write(varBuf[:n])
+
+	n = binary.PutVarint(varBuf, p.DurationInSamples)
+	buf.Write(varBuf[:n])
+
+	n = binary.PutUvarint(varBuf, uint64(len(p.Data)))
+	buf.Write(varBuf[:n])
+
+	buf.Write(p.Data)
+
+	return buf.Bytes()
+}
+
 func (q *Queue) HandleRadioRequest(writer http.ResponseWriter, request *http.Request) {
 	for _, mount := range q.mounts {
 		if strings.HasSuffix(request.URL.Path, mount.Mount) {
@@ -453,7 +500,102 @@ func (q *Queue) HandleRadioRequest(writer http.ResponseWriter, request *http.Req
 			var requestDone error
 			var wgClient sync.WaitGroup
 
-			if numberValue, err := strconv.Atoi(request.Header.Get("icy-metadata")); err == nil && numberValue >= 1 {
+			//set X-Audio-Packet-Stream for strictly timed packets and metadata
+			if numberValue, err := strconv.Atoi(request.Header.Get("x-audio-packet-stream")); err == nil && numberValue == 1 {
+				//version 1
+
+				packetWriteCallback = func(packet packetizer.Packet) error {
+					if requestDone != nil {
+						return requestDone
+					}
+					if metadataPacket, ok := packet.(*QueueMetadataPacket); ok {
+
+						queueInfoBuf := make([]byte, binary.MaxVarintLen64)
+						n := binary.PutVarint(queueInfoBuf, int64(metadataPacket.TrackEntry.QueueIdentifier))
+
+						if len(writeChannel) >= (byteSliceChannelBuffer - 1) {
+							requestDone = errors.New("client ran out of buffer")
+							log.Printf("failed to write data to client: %s\n", requestDone)
+							return requestDone
+						}
+
+						writeChannel <- (&packetStreamFrame{
+							Type:              TrackIdentifier,
+							StartSampleNumber: packet.GetStartSampleNumber(),
+							DurationInSamples: packet.GetEndSampleNumber() - packet.GetStartSampleNumber(),
+							Data:              queueInfoBuf[:n],
+						}).Encode()
+
+						if metadataBytes, err := json.Marshal(metadataPacket.TrackEntry.Metadata); err == nil {
+							if len(writeChannel) >= (byteSliceChannelBuffer - 1) {
+								requestDone = errors.New("client ran out of buffer")
+								log.Printf("failed to write data to client: %s\n", requestDone)
+								return requestDone
+							}
+
+							writeChannel <- (&packetStreamFrame{
+								Type:              TrackMetadata,
+								StartSampleNumber: packet.GetStartSampleNumber(),
+								DurationInSamples: packet.GetEndSampleNumber() - packet.GetStartSampleNumber(),
+								Data:              metadataBytes,
+							}).Encode()
+						}
+						return nil
+					}
+
+					if len(writeChannel) >= (byteSliceChannelBuffer - 1) {
+						requestDone = errors.New("client ran out of buffer")
+						log.Printf("failed to write data to client: %s\n", requestDone)
+						return requestDone
+					}
+
+					//TODO: category
+
+					var frameType packetStreamType
+					switch packet.KeepMode() {
+					case packetizer.KeepLast:
+						frameType = DataKeepLast
+					case packetizer.Keep:
+						frameType = DataKeep
+					case packetizer.GroupKeep:
+						frameType = DataGroupKeep
+					case packetizer.GroupDiscard:
+						frameType = DataGroupDiscard
+					case packetizer.Discard:
+						frameType = DataDiscard
+					default:
+						return errors.New("unknown KeepMode")
+					}
+
+					writeChannel <- (&packetStreamFrame{
+						Type:              frameType,
+						StartSampleNumber: packet.GetStartSampleNumber(),
+						DurationInSamples: packet.GetEndSampleNumber() - packet.GetStartSampleNumber(),
+						Data:              packet.GetData(),
+					}).Encode()
+					return nil
+				}
+
+				type headerData struct {
+					Channels   int64
+					SampleRate int64
+					MimeType   string
+				}
+
+				headerBytes := new(bytes.Buffer)
+
+				binary.Write(headerBytes, binary.LittleEndian, int64(2))
+				binary.Write(headerBytes, binary.LittleEndian, int64(mount.SampleRate))
+				binary.Write(headerBytes, binary.LittleEndian, int32(len(mount.MimeType)))
+				headerBytes.Write([]byte(mount.MimeType))
+
+				writeChannel <- (&packetStreamFrame{
+					Type:              Header,
+					StartSampleNumber: 0,
+					DurationInSamples: 0,
+					Data:              headerBytes.Bytes(),
+				}).Encode()
+			} else if numberValue, err = strconv.Atoi(request.Header.Get("icy-metadata")); err == nil && numberValue >= 1 {
 				metadataToSend := make(map[string]string)
 				const icyInterval = 8192 //weird clients might not support other numbers than this
 				icyCounter := 0