Privacy Policy
Free Shadowing by Silverla Lab
Effective Date: August 9, 2026
Privacy Version: 2026-08-09
Website: https://silverla.co  |  Contact: supernovazyg@gmail.com
2.1 Overview
This Privacy Policy explains how Silverla Lab handles information when you use Free Shadowing. Free Shadowing is currently available for Windows and Android, with other platforms potentially offered later. The App helps users practice English pronunciation by shadowing speech from YouTube videos and receiving automated pronunciation feedback.
2.2 Information We Process
Microphone recordings
When you choose to record a pronunciation attempt, the App accesses your microphone and records your speech. A recording may remain on your device as a WAV file or similar local file for replay or practice-history features.
When you submit a recording for cloud pronunciation scoring, your microphone audio leaves your device. It is uploaded to the Free Shadowing backend and then may be sent with reference text and locale information to Microsoft Azure Speech / Pronunciation Assessment. The backend temporarily writes the upload and any converted WAV file to server storage, then deletes those temporary files after processing, including on error paths. Free Shadowing does not intentionally maintain a lasting server-side archive of pronunciation recordings submitted for scoring.
Account information
If you create an optional Silverla ID, we process information such as your email address, username or display name, password hash, account identifiers, email-verification status and timestamps, and authentication/session information. Passwords are stored as server-side hashes rather than readable plaintext. Email verification tokens expire after 24 hours by default; resending confirmation creates a new token and invalidates the previous one.
YouTube and practice information
When you add or practice an episode, we may process a YouTube URL or video identifier, episode information, caption-derived segment text, selected practice segments, pronunciation scores, number of attempts, timestamps, and information needed to associate activity with a guest session or registered account. Practice audio and scores used only for an assessment request are not persistently stored on the backend after that request unless they are separately submitted as ranking data or stored locally by the App.
Leaderboard information
If you participate in rankings, we may store and display your chosen display name, episode identifier, score, number of attempts, guest/account status, update time, and an internal client identifier. Registered ranking entries may also be associated with your internal Silverla user ID so they can be removed when the account is deleted.
Technical and service information
When you connect to our online services, our servers and hosting infrastructure may process technical information such as IP address, request time, requested endpoint or path, application/device information included in network requests, error information, and operational or security logs. Production application code does not intentionally log passwords, session/Bearer tokens, email-verification tokens, microphone audio, or recognized user speech. Verification-token query values are redacted from application access logs.
2.3 Information Stored on Your Device
Depending on how you use the App, Free Shadowing may store episodes, segments, practice attempts, WAV recordings, preferences, session/authentication tokens, account-mode information, user ID, display name, email, and other information needed for local functionality. Local information generally remains on the device unless a feature requires it to be transmitted, synchronized, or processed remotely.
Deleting your Silverla ID clears account/session information from the App but does not automatically delete local practice WAV recordings or unrelated device-only practice data. Removing the App, clearing application data, or deleting local files may remove locally stored information depending on your operating system and App configuration.
2.4 Information Processed or Stored in the Cloud
Depending on the feature, cloud systems may process account data, authentication information, microphone audio submitted for scoring, reference text, YouTube URLs or video identifiers, caption requests, pronunciation results, leaderboard information, and ordinary operational logs.
Free Shadowing's current cloud API is https://podcast-shadow-zhangyue.fly.dev or a successor endpoint. The hostname may change as infrastructure evolves without changing the purposes described here.
2.5 How We Use Information
Provide Free Shadowing features and maintain guest or registered sessions.
Authenticate users and operate Silverla ID accounts.
Process pronunciation attempts and generate automated scores or feedback.
Prepare practice segments from YouTube captions and metadata.
Operate optional leaderboards and rankings.
Send account confirmation, security, or service-related emails where configured.
Troubleshoot errors, secure the service, prevent abuse, and maintain reliability.
Comply with legal obligations and enforce the Terms of Use.
2.6 Microsoft Azure Speech
Free Shadowing uses Microsoft Azure Speech, including real-time Pronunciation Assessment. For a scoring request, microphone audio, reference text, and locale information may be transmitted to Microsoft for processing. Free Shadowing currently uses the SpeechRecognizer + recognize_once() real-time path with PronunciationAssessmentConfig, rather than a batch-transcription workflow.
Microsoft states in its current documentation that, for real-time speech-to-text and pronunciation assessment, customer-provided data is not retained or stored and real-time audio is processed in server memory rather than stored at rest. Free Shadowing does not enable Azure audio/content logging in application code. Microsoft controls its own infrastructure, policies, and documentation, which may change.
The Azure region is set through AZURE_SPEECH_REGION and currently defaults to East US (eastus).
2.7 YouTube
Practice video is streamed through YouTube rather than downloaded by Silverla Lab as a practice video file. The App may use embedded YouTube players, YouTube thumbnails, caption/metadata endpoints, or open a YouTube watch page. When you interact with YouTube content, YouTube/Google may receive playback, cookie, device, network, and other information according to their own technologies, terms, and privacy practices. YouTube may also show its own advertising or perform its own measurement inside its player. Silverla Lab does not use a YouTube advertising SDK and does not control Google's independent processing.
2.8 Dictionary, Translation, TTS, and Other Feature Providers
For dictionary and translation features, the App may send a looked-up English word to services such as dictionaryapi.dev and MyMemory Translate. Dictionary audio may be fetched from the audio host returned by the dictionary service. Operating-system text-to-speech may process a word locally or, depending on your device settings and TTS engine, through a provider-operated cloud service. These services receive only the information needed for the requested feature, plus normal network information such as source IP and user agent.
2.9 Hosting and Email Providers
Our backend is currently hosted on Fly.io. Fly.io and related infrastructure may process network and operational information necessary to host and secure the service, including IP addresses and application stdout/stderr. Application logs may be retained for a limited operational period by the hosting provider or longer if exported by the operator.
If SMTP email is configured, a transactional email provider may receive your email address, username, and confirmation link/token as needed to deliver account-confirmation messages. Free Shadowing does not intentionally include email-verification tokens in production application logs.
2.10 Sale, Sharing, Advertising, and Analytics
Free Shadowing does not currently sell personal information, use personal information for cross-context behavioral advertising, or include third-party advertising or behavioral-tracking SDKs. The App currently does not include Firebase Analytics, Sentry, AdMob, Meta SDKs, AppsFlyer, Mixpanel, or similar analytics/advertising SDKs.
Some third-party services used to provide App functionality may independently receive information necessary to provide those services. For example, YouTube may receive playback and device-related information, Microsoft Azure Speech receives pronunciation audio and reference text for assessment, dictionary or translation services receive words submitted for lookup, and our hosting provider handles traffic to the backend. These functional disclosures are different from selling personal information or using it for cross-context behavioral advertising.
2.11 Data Retention
2.12 Account and Data Deletion
Registered users can delete their Silverla ID from the App through Account settings. The deletion process removes the account record, email, username, password hash, verification information, username index entry, and active sessions for that user. Registered leaderboard entries reliably associated with that Silverla user ID are also removed.
Some legacy registered ranking rows created before user-ID association was consistently stored may use an older local client identifier and cannot always be reliably matched to the deleted account. Those legacy rows may remain. Guest ranking entries are not removed by deleting a registered account because they are not authenticated to that account.
Deleting an account does not automatically delete local WAV recordings or other device-only practice files. You may need to remove those separately through the App, device, or operating-system controls.
You may also contact supernovazyg@gmail.com with privacy or deletion questions.
2.13 Security
We use reasonable technical and organizational measures appropriate to the service. Current measures include server-side password hashing, authenticated session tokens, verification-token expiration, production log redaction for verification tokens, and temporary-file cleanup for pronunciation audio. Production application code does not intentionally log passwords, session tokens, microphone audio, or recognized user speech. No internet service or storage system can guarantee absolute security.
2.14 Children's Privacy
Free Shadowing is intended for users age 13 or older and is not directed to U.S. children under 13. We do not knowingly seek to collect personal information from children under 13. If we learn that personal information was collected from a child contrary to applicable requirements, we will take reasonable steps to delete it.
If you are under the age at which you can independently consent to use an online service or to the processing of personal information where you live, you may use Free Shadowing only with any legally required parent or guardian authorization. In the EEA, UK, and other jurisdictions, additional age rules may apply, including a default age of 16 for certain data-processing consent where local law does not provide a lower age.
2.15 International Data Transfers
Free Shadowing uses internet-based infrastructure and third-party providers. Information may therefore be processed in countries other than the country where you live, including the United States and locations where our service providers operate. Those countries may have privacy laws different from those in your jurisdiction. Where applicable law requires a specific transfer mechanism or contractual protection, we will use an appropriate mechanism.
2.16 California Privacy Rights
California residents may have rights under the California Consumer Privacy Act, as amended (CCPA/CPRA), to the extent that law applies to Silverla Lab and the particular processing. Depending on applicability, those rights may include the right to know or access personal information, request deletion, request correction, receive information about categories of personal information and disclosures, opt out of sale or sharing, limit certain uses of sensitive personal information where applicable, and exercise rights without unlawful discrimination.
Free Shadowing does not currently sell personal information or use personal information for cross-context behavioral advertising. If those practices change, we will update this Privacy Policy and provide any legally required opt-out mechanism before or when the change takes effect.
California privacy requests may be sent to supernovazyg@gmail.com with the subject "California Privacy Request." We may need to verify your identity before responding. An authorized agent may submit a request where permitted by law, subject to applicable verification requirements.
2.17 Other U.S. State Privacy Rights
Residents of other U.S. states may have additional rights under applicable privacy laws, which may include access, correction, deletion, portability, or certain opt-out rights. Where those laws apply, you may submit a request to supernovazyg@gmail.com and identify the state and type of request. We may request information reasonably necessary to verify the request.
2.18 EEA and UK Users
If European or UK data-protection law applies to a particular user or processing activity, additional rights may apply, including rights of access, correction, deletion, restriction, portability, objection, and complaint to a supervisory authority. The legal basis and specific obligations may depend on the feature used, the user's location and age, and the role of applicable service providers. Nothing in this policy limits rights that applicable law makes non-waivable.
2.19 Automated Pronunciation Assessment
Pronunciation scores and related feedback may be generated automatically. Results can be affected by microphone quality, background noise, accent, speaking speed, caption errors, differences between expected text and actual video speech, and technical limitations of the speech provider. Free Shadowing's scoring is intended as a learning aid and should not be used to make employment, admissions, immigration, medical, or other consequential decisions about a person.
2.20 Changes to This Privacy Policy
We may update this Privacy Policy as Free Shadowing develops. When changes are material, we will provide notice as appropriate through the App, website, email, or another reasonable method. Where applicable law requires consent for a new use of information, we will request that consent. The Effective Date and Privacy Version identify the applicable version.
2.21 Contact Us
Privacy questions or requests may be sent to Silverla Lab at supernovazyg@gmail.com or through https://silverla.co.
