Android (Kotlin)

Most people who will use your app carry an Android phone. This page builds the two halves of a voice feature: a small server route that holds your key, and the Kotlin code that records, uploads and plays.

Android app  ──(your login)──►  your server  ──(NAMU_API_KEY)──►  api.namuai-lab.com

Never put your Namu key in the app. An APK can be unpacked in minutes, and the key would let anyone spend your allowance.

1. The server route

Any server works. Two routes in Python with Flask and the Python library (pip install namu-ai):

server.py

from flask import Flask, request, Response
from namu import Namu, NamuError

app = Flask(__name__)
namu = Namu()

@app.post("/api/transcribe")
def transcribe():
    # 1. check your own user (session, token...) here
    audio = request.files["file"].read()
    try:
        result = namu.transcribe(audio, language=request.form.get("language", "ha"))
    except NamuError as e:
        return {"error": e.type}, e.status
    return {"text": result["text"]}

@app.post("/api/speak")
def speak():
    try:
        audio = namu.speech(request.json["text"], voice=request.json.get("voice", "nadia"), format="mp3")
    except NamuError as e:
        return {"error": e.type}, e.status
    return Response(audio, mimetype="audio/mpeg")

2. Record a voice note

MediaRecorder writes AAC in an M4A file: small, and read by the API as it is. Ask for the microphone permission first (android.permission.RECORD_AUDIO).

Recorder.kt

import android.content.Context
import android.media.MediaRecorder
import java.io.File

class Recorder(private val context: Context) {
    private var recorder: MediaRecorder? = null
    val file: File get() = File(context.cacheDir, "note.m4a")

    fun start() {
        recorder = MediaRecorder(context).apply {
            setAudioSource(MediaRecorder.AudioSource.MIC)
            setOutputFormat(MediaRecorder.OutputFormat.MPEG_4)
            setAudioEncoder(MediaRecorder.AudioEncoder.AAC)
            setAudioChannels(1)          // mono: half the bytes, same words
            setAudioSamplingRate(16_000)
            setAudioEncodingBitRate(32_000)
            setOutputFile(file.absolutePath)
            prepare()
            start()
        }
    }

    fun stop() {
        recorder?.apply { stop(); release() }
        recorder = null
    }
}

MediaRecorder(context) needs Android 12 (API 31); on older versions use MediaRecorder().

3. Send it and read the text

With OkHttp (com.squareup.okhttp3:okhttp). Run it off the main thread, in a coroutine:

VoiceApi.kt

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.withContext
import okhttp3.MediaType.Companion.toMediaType
import okhttp3.MultipartBody
import okhttp3.OkHttpClient
import okhttp3.Request
import okhttp3.RequestBody.Companion.asRequestBody
import okhttp3.RequestBody.Companion.toRequestBody
import org.json.JSONObject
import java.io.File
import java.util.concurrent.TimeUnit

class VoiceApi(private val baseUrl: String, private val token: String) {
    // Generous timeouts: mobile networks are slow, and a model waking up can take a minute.
    private val http = OkHttpClient.Builder()
        .connectTimeout(30, TimeUnit.SECONDS)
        .readTimeout(5, TimeUnit.MINUTES)
        .writeTimeout(2, TimeUnit.MINUTES)
        .build()

    suspend fun transcribe(note: File, language: String = "ha"): String = withContext(Dispatchers.IO) {
        val body = MultipartBody.Builder().setType(MultipartBody.FORM)
            .addFormDataPart("file", note.name, note.asRequestBody("audio/mp4".toMediaType()))
            .addFormDataPart("language", language)
            .build()
        val request = Request.Builder().url("$baseUrl/api/transcribe")
            .header("Authorization", "Bearer $token")   // your user's token, not the Namu key
            .post(body).build()
        http.newCall(request).execute().use { response ->
            val json = JSONObject(response.body!!.string())
            if (!response.isSuccessful) error(json.optString("error", "failed"))
            json.getString("text")
        }
    }

    suspend fun speak(text: String, into: File): File = withContext(Dispatchers.IO) {
        val body = JSONObject(mapOf("text" to text, "voice" to "nadia")).toString()
            .toRequestBody("application/json".toMediaType())
        val request = Request.Builder().url("$baseUrl/api/speak")
            .header("Authorization", "Bearer $token").post(body).build()
        http.newCall(request).execute().use { response ->
            if (!response.isSuccessful) error("speak failed: ${response.code}")
            into.outputStream().use { response.body!!.byteStream().copyTo(it) }
        }
        into
    }
}

4. Play the answer

val reply = api.speak("Na gode! Mun karɓi saƙonku.", File(cacheDir, "reply.mp3"))
MediaPlayer().apply {
    setDataSource(reply.absolutePath)
    setOnCompletionListener { release() }
    prepare()
    start()
}

Keep note.m4a until the transcription succeeds: if the network drops, retry from the file instead of asking the person to speak again. More habits in building for weak networks.

Get started

SDKs and tools

Mobile apps

Resources

1. The server route

2. Record a voice note

3. Send it and read the text

4. Play the answer

​1. The server route

​2. Record a voice note

​3. Send it and read the text

​4. Play the answer

1. The server route

2. Record a voice note

3. Send it and read the text

4. Play the answer