Function ModelTranscriptionLive

core/backend/transcript_live.go:205–278

ModelTranscriptionLive loads the transcription backend, opens the bidirectional AudioTranscriptionLive RPC, sends the session config, and BLOCKS until the backend's ready ack. A grpcerrors. IsLiveTranscriptionUnsupported error means the backend (or the loaded model) cannot do live transcription and

(ctx context.Context, language string,
	ml *model.ModelLoader, modelConfig config.ModelConfig, appConfig *config.ApplicationConfig,
	onEvent func(LiveTranscriptionEvent))

// background goroutine — in order, one event at a time — for every response
// the backend streams, ending with the Final event triggered by Close.
func ModelTranscriptionLive(ctx context.Context, language string,
	ml *model.ModelLoader, modelConfig config.ModelConfig, appConfig *config.ApplicationConfig,
	onEvent func(LiveTranscriptionEvent)) (LiveTranscriptionSession, error) {

	transcriptionModel, err := loadTranscriptionModel(ctx, ml, modelConfig, appConfig)
	if err != nil {
		return nil, err
	}

	// The derived cancel out-lives this call inside the session: Close uses
	// it to unwind the stream (and, in embed mode, the server-side recv
	// pump, which only stops on send-close or context cancellation).
	streamCtx, cancel := context.WithCancel(ctx)
	stream, err := transcriptionModel.AudioTranscriptionLive(streamCtx)
	if err != nil {
		cancel()
		return nil, err
	}

	fail := func(err error) (LiveTranscriptionSession, error) {
		_ = stream.CloseSend()
		cancel()
		return nil, err
	}

	if err := stream.Send(&proto.TranscriptLiveRequest{
		Payload: &proto.TranscriptLiveRequest_Config{Config: &proto.TranscriptLiveConfig{
			Language:   language,
			SampleRate: liveSampleRate,
		}},
	}); err != nil {
		return fail(err)
	}

	// Ready-ack contract: the backend answers a successful open with a
	// {ready:true} response before any transcript data; unsupported
	// backends surface Unimplemented here instead.
	ack, err := stream.Recv()
	if err != nil {
		return fail(err)
	}
	if !ack.GetReady() {
		return fail(fmt.Errorf("live transcription: backend %q broke the ready-ack contract (first response carried data)", modelConfig.Backend))
	}

	s := &liveTranscriptionSession{
		stream:   stream,
		cancel:   cancel,
		recvDone: make(chan struct{}),
		trace:    newLiveTraceState(modelConfig, appConfig, language),
	}

	go func() {
		defer close(s.recvDone)
		for {
			resp, err := stream.Recv()
			if err != nil {
				if !errors.Is(err, io.EOF) && streamCtx.Err() == nil {