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feature/pcmu-to-aac #265

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a7e6895
Implement PCM_MULAW to AAC transcoding functionality
cedricve Mar 19, 2026
945ceea
Add LPCM audio support and enhance PCM_MULAW to AAC transcoding
cedricve Mar 19, 2026
204ae3f
Refactor PCM to AAC transcoder for improved concurrency and error han…
cedricve Mar 19, 2026
642a89a
Enhance audio/video synchronization and improve flushing timeout in A…
cedricve Mar 19, 2026
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86 changes: 86 additions & 0 deletions machinery/src/capture/gortsplib.go
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Original file line number Diff line number Diff line change
Expand Up @@ -339,6 +339,40 @@ func (g *Golibrtsp) Connect(ctx context.Context, ctxOtel context.Context) (err e
}
}

// Look for audio stream.
// find the LPCM media and format
audioFormaLPCM, audioMediLPCM := FindLPCM(desc, false)
g.AudioLPCMMedia = audioMediLPCM
g.AudioLPCMForma = audioFormaLPCM
if audioMediLPCM == nil {
log.Log.Debug("capture.golibrtsp.Connect(LPCM): " + "audio media not found")
} else {
_, err = g.Client.Setup(desc.BaseURL, audioMediLPCM, 0, 0)
if err != nil {
log.Log.Error("capture.golibrtsp.Connect(LPCM): " + err.Error())
} else {
audiortpDec, err := audioFormaLPCM.CreateDecoder()
if err != nil {
log.Log.Error("capture.golibrtsp.Connect(LPCM): " + err.Error())
} else {
g.AudioLPCMDecoder = audiortpDec
streamIndex := len(g.Streams)
g.Streams = append(g.Streams, packets.Stream{
Index: streamIndex,
Name: "LPCM",
IsVideo: false,
IsAudio: true,
IsBackChannel: false,
SampleRate: audioFormaLPCM.SampleRate,
Channels: audioFormaLPCM.ChannelCount,
BitDepth: audioFormaLPCM.BitDepth,
})

g.AudioLPCMIndex = int8(len(g.Streams)) - 1
}
}
}

// Look for audio stream.
// find the G711 media and format
audioForma, audioMedi := FindPCMU(desc, false)
Expand Down Expand Up @@ -367,6 +401,8 @@ func (g *Golibrtsp) Connect(ctx context.Context, ctxOtel context.Context) (err e
IsVideo: false,
IsAudio: true,
IsBackChannel: false,
SampleRate: defaultPCMUSampleRate,
Channels: defaultPCMUChannels,
})

// Set the index for the audio
Expand Down Expand Up @@ -509,6 +545,8 @@ func (g *Golibrtsp) ConnectBackChannel(ctx context.Context, ctxRunAgent context.
IsVideo: false,
IsAudio: true,
IsBackChannel: true,
SampleRate: defaultPCMUSampleRate,
Channels: defaultPCMUChannels,
})
// Set the index for the audio
g.AudioG711IndexBackChannel = int8(len(g.Streams)) - 1
Expand All @@ -521,6 +559,39 @@ func (g *Golibrtsp) ConnectBackChannel(ctx context.Context, ctxRunAgent context.
func (g *Golibrtsp) Start(ctx context.Context, streamType string, queue *packets.Queue, configuration *models.Configuration, communication *models.Communication) (err error) {
log.Log.Debug("capture.golibrtsp.Start(): started")

// called when a MULAW audio RTP packet arrives
if g.AudioLPCMMedia != nil && g.AudioLPCMForma != nil {
g.Client.OnPacketRTP(g.AudioLPCMMedia, g.AudioLPCMForma, func(rtppkt *rtp.Packet) {
pts, ok := g.Client.PacketPTS(g.AudioLPCMMedia, rtppkt)
pts2, ok := g.Client.PacketPTS2(g.AudioLPCMMedia, rtppkt)
if !ok {
log.Log.Debug("capture.golibrtsp.Start(): " + "unable to get PTS")
return
}
Comment on lines +565 to +570

op, err := g.AudioLPCMDecoder.Decode(rtppkt)
if err != nil {
log.Log.Error("capture.golibrtsp.Start(): " + err.Error())
return
}

pkt := packets.Packet{
IsKeyFrame: false,
Packet: rtppkt,
Data: op,
Time: pts2,
TimeLegacy: pts,
CompositionTime: pts2,
CurrentTime: time.Now().UnixMilli(),
Idx: g.AudioLPCMIndex,
IsVideo: false,
IsAudio: true,
Codec: "LPCM",
}
queue.WritePacket(pkt)
})
}

// called when a MULAW audio RTP packet arrives
if g.AudioG711Media != nil && g.AudioG711Forma != nil {
g.Client.OnPacketRTP(g.AudioG711Media, g.AudioG711Forma, func(rtppkt *rtp.Packet) {
Expand Down Expand Up @@ -1259,6 +1330,21 @@ func FindPCMU(desc *description.Session, isBackChannel bool) (*format.G711, *des
return nil, nil
}

func FindLPCM(desc *description.Session, isBackChannel bool) (*format.LPCM, *description.Media) {
for _, media := range desc.Medias {
if media.IsBackChannel == isBackChannel {
for _, forma := range media.Formats {
if lpcm, ok := forma.(*format.LPCM); ok {
if lpcm.SampleRate > 0 && lpcm.ChannelCount > 0 && lpcm.BitDepth > 0 {
return lpcm, media
}
}
}
}
}
return nil, nil
}

func FindOPUS(desc *description.Session, isBackChannel bool) (*format.Opus, *description.Media) {
for _, media := range desc.Medias {
if media.IsBackChannel == isBackChannel {
Expand Down
128 changes: 78 additions & 50 deletions machinery/src/capture/main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -87,13 +87,31 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
// We only expect one audio and one video codec.
// If there are multiple audio or video streams, we will use the first one.
audioCodec := ""
audioBitDepth := 0
videoCodec := ""
configuredAudioSampleRate := config.Capture.IPCamera.SampleRate
configuredAudioChannels := config.Capture.IPCamera.Channels
audioStreams, _ := rtspClient.GetAudioStreams()
videoStreams, _ := rtspClient.GetVideoStreams()
if len(audioStreams) > 0 {
audioCodec = audioStreams[0].Name
config.Capture.IPCamera.SampleRate = audioStreams[0].SampleRate
config.Capture.IPCamera.Channels = audioStreams[0].Channels
resolvedSampleRate := audioStreams[0].SampleRate
resolvedChannels := audioStreams[0].Channels

if audioCodec == "LPCM" {
if configuredAudioSampleRate > 0 && configuredAudioSampleRate != resolvedSampleRate {
log.Log.Warning("capture.main.HandleRecordStream(): LPCM sample rate mismatch between configuration and RTSP stream; using configured value " + strconv.Itoa(configuredAudioSampleRate) + " instead of detected value " + strconv.Itoa(resolvedSampleRate))
resolvedSampleRate = configuredAudioSampleRate
}
if configuredAudioChannels > 0 && configuredAudioChannels != resolvedChannels {
log.Log.Warning("capture.main.HandleRecordStream(): LPCM channel count mismatch between configuration and RTSP stream; using configured value " + strconv.Itoa(configuredAudioChannels) + " instead of detected value " + strconv.Itoa(resolvedChannels))
resolvedChannels = configuredAudioChannels
}
}

config.Capture.IPCamera.SampleRate = resolvedSampleRate
config.Capture.IPCamera.Channels = resolvedChannels
audioBitDepth = audioStreams[0].BitDepth
}
if len(videoStreams) > 0 {
videoCodec = videoStreams[0].Name
Expand All @@ -105,13 +123,15 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
//var cws *cacheWriterSeeker
var mp4Video *video.MP4
var videoTrack uint32
var audioTrack uint32
var audioWriter *recordingAudioWriter
var name string

// Do not do anything!
log.Log.Info("capture.main.HandleRecordStream(continuous): start recording")

start := false
rolloverRequested := false
rolloverMaxLogged := false

// If continuous record the full length
postRecording = maxRecordingPeriod
Expand All @@ -136,9 +156,18 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
nextPkt, cursorError = recordingCursor.ReadPacket()

now := time.Now().UnixMilli()
hardMaxReached := now-startRecording > maxRecordingPeriod-500
postRecordingElapsed := startRecording+postRecording-now <= 0
if start && (postRecordingElapsed || hardMaxReached) {
rolloverRequested = true
if hardMaxReached && !rolloverMaxLogged {
log.Log.Info("capture.main.HandleRecordStream(continuous): max recording period reached, waiting for next keyframe to roll over without dropping frames")
rolloverMaxLogged = true
}
}

if start && // If already recording and current frame is a keyframe and we should stop recording
nextPkt.IsKeyFrame && (startRecording+postRecording-now <= 0 || now-startRecording > maxRecordingPeriod-500) {
rolloverRequested && nextPkt.IsKeyFrame {

pts := convertPTS(pkt.TimeLegacy)
if pkt.IsVideo {
Expand All @@ -147,17 +176,17 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.IsAudio {
// Write the last packet
if pkt.Codec == "AAC" {
if err := mp4Video.AddSampleToTrack(audioTrack, pkt.IsKeyFrame, pkt.Data, pts); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.Codec == "PCM_MULAW" {
// TODO: transcode to AAC, some work to do..
log.Log.Debug("capture.main.HandleRecordStream(continuous): no AAC audio codec detected, skipping audio track.")
if err := audioWriter.WritePacket(pkt); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
}

if err := audioWriter.Flush(); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
audioWriter.Close()
audioWriter = nil

// Close mp4
if len(mp4Video.SPSNALUs) == 0 && len(configuration.Config.Capture.IPCamera.SPSNALUs) > 0 {
mp4Video.SPSNALUs = configuration.Config.Capture.IPCamera.SPSNALUs
Expand All @@ -177,6 +206,8 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat

// Cleanup muxer
start = false
rolloverRequested = false
rolloverMaxLogged = false

// Update the name of the recording with the duration.
// We will update the name of the recording with the duration in milliseconds.
Expand Down Expand Up @@ -305,27 +336,16 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
} else if videoCodec == "H265" {
videoTrack = mp4Video.AddVideoTrack("H265")
}
if audioCodec == "AAC" {
audioTrack = mp4Video.AddAudioTrack("AAC")
} else if audioCodec == "PCM_MULAW" {
log.Log.Debug("capture.main.HandleRecordStream(continuous): no AAC audio codec detected, skipping audio track.")
}
audioWriter = newRecordingAudioWriter(mp4Video, audioCodec, config.Capture.IPCamera.SampleRate, config.Capture.IPCamera.Channels, audioBitDepth, "capture.main.HandleRecordStream(continuous)")

pts := convertPTS(pkt.TimeLegacy)
if pkt.IsVideo {
if err := mp4Video.AddSampleToTrack(videoTrack, pkt.IsKeyFrame, pkt.Data, pts); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.IsAudio {
if pkt.Codec == "AAC" {
if err := mp4Video.AddSampleToTrack(audioTrack, pkt.IsKeyFrame, pkt.Data, pts); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.Codec == "PCM_MULAW" {
// TODO: transcode to AAC, some work to do..
// We might need to use ffmpeg to transcode the audio to AAC.
// For now we will skip the audio track.
log.Log.Debug("capture.main.HandleRecordStream(continuous): no AAC audio codec detected, skipping audio track.")
if err := audioWriter.WritePacket(pkt); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
}
recordingStatus = "started"
Expand All @@ -339,13 +359,8 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.IsAudio {
if pkt.Codec == "AAC" {
if err := mp4Video.AddSampleToTrack(audioTrack, pkt.IsKeyFrame, pkt.Data, pts); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
} else if pkt.Codec == "PCM_MULAW" {
// TODO: transcode to AAC, some work to do..
log.Log.Debug("capture.main.HandleRecordStream(continuous): no AAC audio codec detected, skipping audio track.")
if err := audioWriter.WritePacket(pkt); err != nil {
log.Log.Error("capture.main.HandleRecordStream(continuous): " + err.Error())
}
}
}
Expand All @@ -355,6 +370,10 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
// We might have interrupted the recording while restarting the agent.
// If this happens we need to check to properly close the recording.
if cursorError != nil {
if audioWriter != nil {
audioWriter.Close()
audioWriter = nil
}
if recordingStatus == "started" {

log.Log.Info("capture.main.HandleRecordStream(continuous): Recording finished: file save: " + name)
Expand Down Expand Up @@ -434,7 +453,6 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
var displayTime int64 = 0 // display time in milliseconds

var videoTrack uint32
var audioTrack uint32

for motion := range communication.HandleMotion {

Expand All @@ -448,6 +466,8 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
motionTimestamp := now

start := false
rolloverRequested := false
rolloverMaxLogged := false

if cursorError == nil {
pkt, cursorError = recordingCursor.ReadPacket()
Expand Down Expand Up @@ -520,6 +540,7 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
}
// Create the MP4 only once the first keyframe arrives.
var mp4Video *video.MP4
var audioWriter *recordingAudioWriter

for cursorError == nil {

Expand All @@ -538,7 +559,17 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
default:
}

if start && (motionTimestamp+postRecording-now < 0 || now-startRecording > maxRecordingPeriod-500) && nextPkt.IsKeyFrame {
hardMaxReached := now-startRecording > maxRecordingPeriod-500
postRecordingElapsed := motionTimestamp+postRecording-now < 0
if start && (postRecordingElapsed || hardMaxReached) {
rolloverRequested = true
if hardMaxReached && !rolloverMaxLogged {
log.Log.Info("capture.main.HandleRecordStream(motiondetection): max recording period reached, waiting for next keyframe to close without dropping frames")
rolloverMaxLogged = true
}
}

if start && rolloverRequested && nextPkt.IsKeyFrame {
log.Log.Info("capture.main.HandleRecordStream(motiondetection): timestamp+postRecording-now < 0 - " + strconv.FormatInt(motionTimestamp+postRecording-now, 10) + " < 0")
log.Log.Info("capture.main.HandleRecordStream(motiondetection): now-startRecording > maxRecordingPeriod-500 - " + strconv.FormatInt(now-startRecording, 10) + " > " + strconv.FormatInt(maxRecordingPeriod-500, 10))
log.Log.Info("capture.main.HandleRecordStream(motiondetection): closing recording (timestamp: " + strconv.FormatInt(motionTimestamp, 10) + ", postRecording: " + strconv.FormatInt(postRecording, 10) + ", now: " + strconv.FormatInt(now, 10) + ", startRecording: " + strconv.FormatInt(startRecording, 10) + ", maxRecordingPeriod: " + strconv.FormatInt(maxRecordingPeriod, 10))
Expand All @@ -563,11 +594,7 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
} else if videoCodec == "H265" {
videoTrack = mp4Video.AddVideoTrack("H265")
}
if audioCodec == "AAC" {
audioTrack = mp4Video.AddAudioTrack("AAC")
} else if audioCodec == "PCM_MULAW" {
log.Log.Debug("capture.main.HandleRecordStream(continuous): no AAC audio codec detected, skipping audio track.")
}
audioWriter = newRecordingAudioWriter(mp4Video, audioCodec, config.Capture.IPCamera.SampleRate, config.Capture.IPCamera.Channels, audioBitDepth, "capture.main.HandleRecordStream(motiondetection)")
start = true
}
if start {
Expand All @@ -581,17 +608,10 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
}
} else if pkt.IsAudio {
log.Log.Debug("capture.main.HandleRecordStream(motiondetection): add audio sample")
if pkt.Codec == "AAC" {
if mp4Video != nil {
if err := mp4Video.AddSampleToTrack(audioTrack, pkt.IsKeyFrame, pkt.Data, pts); err != nil {
log.Log.Error("capture.main.HandleRecordStream(motiondetection): " + err.Error())
}
if mp4Video != nil {
if err := audioWriter.WritePacket(pkt); err != nil {
log.Log.Error("capture.main.HandleRecordStream(motiondetection): " + err.Error())
}
} else if pkt.Codec == "PCM_MULAW" {
// TODO: transcode to AAC, some work to do..
// We might need to use ffmpeg to transcode the audio to AAC.
// For now we will skip the audio track.
log.Log.Debug("capture.main.HandleRecordStream(motiondetection): no AAC audio codec detected, skipping audio track.")
}
}
}
Expand All @@ -604,10 +624,18 @@ func HandleRecordStream(queue *packets.Queue, configDirectory string, configurat
lastRecordingTime = pkt.CurrentTime

if mp4Video == nil {
if audioWriter != nil {
audioWriter.Close()
}
log.Log.Warning("capture.main.HandleRecordStream(motiondetection): recording closed without keyframe; no MP4 created")
continue
}

if err := audioWriter.Flush(); err != nil {
log.Log.Error("capture.main.HandleRecordStream(motiondetection): " + err.Error())
}
audioWriter.Close()

// This will close the recording and write the last packet.
if len(mp4Video.SPSNALUs) == 0 && len(configuration.Config.Capture.IPCamera.SPSNALUs) > 0 {
mp4Video.SPSNALUs = configuration.Config.Capture.IPCamera.SPSNALUs
Expand Down
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