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/**
* Voice-over recording via MediaRecorder.
* Pure helpers (mime type picking, file extension, elapsed formatting, error
* messages) are exported for unit tests; the recorder singleton below owns the
* actual microphone stream.
*/
export const PREFERRED_MIME_TYPES = [
"audio/webm;codecs=opus",
"audio/webm",
"audio/ogg;codecs=opus",
"audio/ogg",
"audio/mp4",
] as const;
export function pickSupportedMimeType({
isTypeSupported,
candidates = PREFERRED_MIME_TYPES,
}: {
isTypeSupported: (mimeType: string) => boolean;
candidates?: readonly string[];
}): string | null {
for (const mimeType of candidates) {
if (isTypeSupported(mimeType)) {
return mimeType;
}
}
return null;
}
const EXTENSION_BY_MIME_SUBTYPE: Record<string, string> = {
webm: "webm",
ogg: "ogg",
mp4: "m4a",
mpeg: "mp3",
wav: "wav",
};
export function getFileExtensionForMimeType({
mimeType,
}: {
mimeType: string;
}): string {
const subtype = mimeType.split("/").at(1)?.split(";").at(0)?.trim() ?? "";
return EXTENSION_BY_MIME_SUBTYPE[subtype] ?? "audio";
}
export function formatElapsedSeconds({
seconds,
}: {
seconds: number;
}): string {
const totalSeconds = Math.max(0, Math.floor(seconds));
const minutes = Math.floor(totalSeconds / 60);
const remainder = totalSeconds % 60;
return `${minutes}:${String(remainder).padStart(2, "0")}`;
}
export function getVoiceOverErrorMessage({
error,
}: {
error: unknown;
}): string {
if (error instanceof DOMException) {
switch (error.name) {
case "NotAllowedError":
case "SecurityError":
return "Microphone access denied. Allow microphone access in your browser settings to record a voice-over.";
case "NotFoundError":
case "OverconstrainedError":
return "No microphone found. Connect a microphone and try again.";
case "NotReadableError":
return "The microphone is already in use by another application.";
default:
return "Could not start voice-over recording.";
}
}
if (error instanceof Error && error.message) {
return error.message;
}
return "Could not start voice-over recording.";
}
export interface VoiceOverRecordingResult {
blob: Blob;
mimeType: string;
durationSeconds: number;
}
interface ActiveRecording {
recorder: MediaRecorder;
stream: MediaStream;
chunks: Blob[];
mimeType: string;
startedAtMs: number;
}
let activeRecording: ActiveRecording | null = null;
function stopStreamTracks({ stream }: { stream: MediaStream }): void {
for (const track of stream.getTracks()) {
track.stop();
}
}
export async function startVoiceOverRecording(): Promise<void> {
if (activeRecording) {
throw new Error("A voice-over recording is already in progress");
}
const mediaDevices = navigator.mediaDevices;
if (!mediaDevices?.getUserMedia) {
throw new Error("Voice-over recording is not supported in this browser");
}
const stream = await mediaDevices.getUserMedia({ audio: true });
try {
const mimeType = pickSupportedMimeType({
isTypeSupported: (candidate) => MediaRecorder.isTypeSupported(candidate),
});
const recorder = mimeType
? new MediaRecorder(stream, { mimeType })
: new MediaRecorder(stream);
const chunks: Blob[] = [];
recorder.addEventListener("dataavailable", (event) => {
if (event.data.size > 0) {
chunks.push(event.data);
}
});
recorder.start();
activeRecording = {
recorder,
stream,
chunks,
mimeType: recorder.mimeType || mimeType || "audio/webm",
startedAtMs: performance.now(),
};
} catch (error) {
stopStreamTracks({ stream });
throw error;
}
}
export function stopVoiceOverRecording(): Promise<VoiceOverRecordingResult> {
const recording = activeRecording;
if (!recording) {
return Promise.reject(
new Error("No voice-over recording is in progress"),
);
}
activeRecording = null;
const { promise, resolve, reject } =
Promise.withResolvers<VoiceOverRecordingResult>();
recording.recorder.addEventListener("stop", () => {
stopStreamTracks({ stream: recording.stream });
resolve({
blob: new Blob(recording.chunks, { type: recording.mimeType }),
mimeType: recording.mimeType,
durationSeconds: Math.max(
0,
(performance.now() - recording.startedAtMs) / 1000,
),
});
});
recording.recorder.addEventListener("error", () => {
stopStreamTracks({ stream: recording.stream });
reject(new Error("Voice-over recording failed"));
});
recording.recorder.stop();
return promise;
}
export function cancelVoiceOverRecording(): void {
const recording = activeRecording;
if (!recording) {
return;
}
activeRecording = null;
try {
recording.recorder.stop();
} catch {
// recorder may already be stopped; tracks are released either way
}
stopStreamTracks({ stream: recording.stream });
}
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