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Architecture

This page shows dengjen-tts’s own structure as a C4 Container, Component, and Code diagram. For how it fits into the wider ZirekHQ speech stack, see the org-wide System Context diagram.

Container

dengjen-tts is a single Rust workspace exposing the same synthesis engine through four different frontends. Go and Java bindings call the C ABI frontend directly rather than being separate frontends of their own.

C4Container
    Person(caller, "Caller", "CLI user, bound language, or another process")

    System_Boundary(dengjen, "dengjen-tts") {
        Container(cli, "dengjen", "Rust binary")
        Container(capi, "libdengjen", "C ABI", "Consumed by the Go and Java bindings")
        Container(pyext, "pydengjen", "Python extension")
        Container(grpc, "dengjen-tts-grpc", "gRPC server", "Vendored by dengjen-nvda")
        Container(engine, "Synthesis engine", "Rust library", "See Component diagram")
    }

    Rel(caller, cli, "Invokes")
    Rel(caller, capi, "Calls, via Go/Java bindings")
    Rel(caller, pyext, "Imports")
    Rel(caller, grpc, "Calls over gRPC")
    Rel(cli, engine, "Uses")
    Rel(capi, engine, "Uses")
    Rel(pyext, engine, "Uses")
    Rel(grpc, engine, "Uses")

Component

The engine’s model backends (Piper, Kokoro, MeloTTS) implement a shared DengjenModel trait; the engine itself wraps a chosen model in a decorator that adds prosody post-processing and parallel/batched dispatch.

C4Component
    Container_Boundary(engine, "Synthesis engine") {
        Component(core, "dengjen-tts-core", "Rust crate", "Defines the DengjenModel trait and shared types (Audio, SynthesisConfig, DengjenError)")
        Component(synth, "DengjenSpeechSynthesizer", "Rust struct (dengjen-tts / synth crate)", "Wraps an inner DengjenModel; applies prosody and dispatches via a rayon thread pool")
        Component(piper, "dengjen-tts-piper", "Rust crate", "VitsModel / VitsStreamingModel")
        Component(kokoro, "dengjen-tts-kokoro", "Rust crate", "KokoroModel")
        Component(melotts, "dengjen-tts-melotts", "Rust crate", "MeloTTSModel")
        Component(sonic, "dengjen-sonic-sys", "FFI binding", "libsonic, used for prosody (pitch/speed) adjustment")
    }

    Rel(synth, core, "Implements")
    Rel(piper, core, "Implements")
    Rel(kokoro, core, "Implements")
    Rel(melotts, core, "Implements")
    Rel(synth, piper, "Wraps one model, e.g.")
    Rel(synth, sonic, "Post-processes via")

Code

The interesting shape here is that DengjenSpeechSynthesizer is a decorator: it implements the exact same DengjenModel trait it wraps, rather than exposing a separate API for "a model with prosody applied."

classDiagram
    class DengjenModel {
        <<trait>>
        +phonemize_text()
        +speak_batch()
        +speak_one_sentence()
        +audio_output_info()
    }
    class VitsModel
    class VitsStreamingModel
    class KokoroModel
    class MeloTTSModel
    class DengjenSpeechSynthesizer {
        -backend: Arc~DengjenModel~
        +speak_batch()
    }

    DengjenModel <|.. VitsModel
    DengjenModel <|.. VitsStreamingModel
    DengjenModel <|.. KokoroModel
    DengjenModel <|.. MeloTTSModel
    DengjenModel <|.. DengjenSpeechSynthesizer
    DengjenSpeechSynthesizer o-- DengjenModel : wraps

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