dss-codec

dss-codec

Web Assembly of gaspardpetit/dss-codec

---

dss-codec is a WASM-based decoder for Olympus .dss and .ds2 dictation audio files. It works in browser and Node.js environments and can decode encrypted DS2 input when a password is provided.

For codec internals and deeper technical background, see dss-codec/README.md and dss-codec/CODEC_SPECIFICATION.md.

Capabilities

Input	Machine-readable format	Native rate	Notes
Olympus .dss	dss_sp	11025 Hz	DSS SP
Grundig/PH9607 .dss	grundig_sp	16000 Hz	Grundig DSS SP
.ds2 standard-play	ds2_sp	12000 Hz	DS2 SP
.ds2 quality-play mode 6	ds2_qp	16000 Hz	DS2 QP
.ds2 quality-play mode 7	ds2_qp7	16000 Hz	DS2 QP7
Encrypted .ds2	A corresponding ds2_* format after inspection/decode	12000 or 16000 Hz	Password required for decode or decrypt

• inspect(...) reports format, nativeRate, and encryption.
• encryption is a stable machine-readable identifier such as none, ds2_aes_128, or ds2_aes_256.
• Decoded audio exposed to JavaScript is mono Float32Array PCM normalized to [-1.0, 1.0].
• decrypt(...) and decryptWithPassword(...) return plain container bytes. For encrypted DS2 input, this normalizes back to plain .ds2 bytes.

Install

npm install dss-codec

• Node.js >=18 is required.
• The package ships entrypoints for bundlers, browser apps, direct browser module loading, and Node.js consumers.

Demo

• Hosted demo: https://gaspardpetit.github.io/dss-codec-wasm/

The repository includes a plain HTML reference integration in examples/simple-html. It inspects DSS and DS2 files in the browser, prompts for a password when needed, decodes to PCM, builds a WAV for playback, and draws a waveform locally in the browser.

• Local demo: npm run demo
• Standalone demo build: npm run build:standalone

Quick Start

import { readFile } from "node:fs/promises";
import { decode, decodeWithPassword, inspect } from "dss-codec";

const bytes = new Uint8Array(await readFile("recording.ds2"));
const inspection = inspect(bytes);

try {
  const password =
    inspection.encryption === "none"
      ? undefined
      : new TextEncoder().encode("1234");

  const result = password
    ? decodeWithPassword(bytes, password)
    : decode(bytes);

  try {
    console.log(result.format);      // "dss_sp" | "grundig_sp" | "ds2_sp" | "ds2_qp" | "ds2_qp7"
    console.log(result.nativeRate);  // 11025 | 12000 | 16000
    console.log(result.samples);     // Float32Array mono PCM in [-1, 1]
  } finally {
    result.free();
  }
} finally {
  inspection.free();
}

Use inspect(...) first when the caller may receive a mix of plain and encrypted inputs. If the source is encrypted, pass password bytes to decodeWithPassword(...).

Entrypoints

• dss-codec: default package entry for Node.js and most bundler/browser usage.
• dss-codec/web: browser-oriented entry with explicit async init(...) control for WASM loading.
• dss-codec/wasm: public WASM asset export for toolchains that need the .wasm file URL explicitly.

Bundlers And Workers

dss-codec/web already falls back to runtime-relative WASM loading with new URL("dss_codec_wasm_bg.wasm", import.meta.url). Some worker and bundler setups handle dependency assets more reliably when the WASM file is imported explicitly:

import init, { decode } from "dss-codec/web";
import wasmUrl from "dss-codec/wasm?url";

await init(wasmUrl);

const result = decode(fileBytes);
try {
  console.log(result.nativeRate);
} finally {
  result.free();
}

For direct browser module usage without a bundler, import from dss-codec/web and await init(...) before calling the decode APIs.

API Overview

Inspection

• inspect(data: Uint8Array) -> InspectResult
• isEncryptedDs2(data: Uint8Array) -> boolean

InspectResult exposes:

• format: string
• nativeRate: number
• encryption: string

Full Decode

• decode(data: Uint8Array) -> DecodeResult
• decodeWithPassword(data: Uint8Array, password: Uint8Array) -> DecodeResult

DecodeResult exposes:

• format: string
• nativeRate: number
• samples: Float32Array

Container Decryption

• decrypt(data: Uint8Array) -> Uint8Array
• decryptWithPassword(data: Uint8Array, password: Uint8Array) -> Uint8Array

These APIs return plain container bytes. They are useful when the caller needs normalized .ds2 bytes instead of decoded PCM.

Streaming Decode

• new StreamDecoder()
• StreamDecoder.withPassword(password: Uint8Array)
• streamer.push(chunk: Uint8Array) -> Float32Array
• streamer.finish() -> Float32Array
• streamer.format -> string | undefined
• streamer.nativeRate -> number | undefined

import { StreamDecoder, inspect } from "dss-codec";

const header = fileChunks[0];
const inspection = inspect(header);

let streamer;
try {
  streamer =
    inspection.encryption === "none"
      ? new StreamDecoder()
      : StreamDecoder.withPassword(new TextEncoder().encode("1234"));
} finally {
  inspection.free();
}

const pcmChunks = [];

try {
  for (const chunk of fileChunks) {
    const samples = streamer.push(chunk);
    if (samples.length > 0) {
      pcmChunks.push(samples);
    }

    console.log(streamer.format);      // may be undefined until enough input is buffered
    console.log(streamer.nativeRate);  // may be undefined until format detection completes
  }

  const tail = streamer.finish();
  if (tail.length > 0) {
    pcmChunks.push(tail);
  }
} finally {
  streamer.free();
}

Returned Data And Integration Notes

• DecodeResult and InspectResult are WASM-backed objects. Read their properties, then call free() when finished.
• Password-taking APIs expect password bytes, not a JavaScript string. Use new TextEncoder().encode(passwordString) when needed.
• nativeRate is the source format's native sample rate. The package does not resample during JavaScript decode.
• Decoded samples are always mono PCM. Convert or resample them in application code if a downstream system requires another layout.
• inspect(...) is useful when deciding whether to call decode(...) or decodeWithPassword(...).

Development

Prerequisites:

• Rust with wasm32-unknown-unknown
• wasm-bindgen-cli
• Node.js 18+
• The ext/dss-codec git submodule checked out locally

Build package artifacts:

git submodule update --init --recursive
rustup target add wasm32-unknown-unknown
cargo install wasm-bindgen-cli --version 0.2.126

npm run build

This generates:

• dist/browser for bundlers and browser apps
• dist/node for Node.js consumers
• dist/web for direct browser module usage with explicit init(...)

Verify the packed npm artifact as installed by consumers:

npm run test:pack

Publishing is tag-driven. The npm publish workflow uses Git tags such as v1.0.0 as the release version source of truth.