Microphone

A redroid device has no microphone of its own: apps that record hear silence. The Microphone card on the session page replaces what they hear, for every app and every kind of recording (voice notes, speech recognition, calls in a WebView), until you turn it off.

Source	What apps hear
Off	Silence, the device’s own microphone
Line-up tone	A steady 1 kHz tone at −18 dBFS, the broadcast test tone
Beeps	A 100 ms 1 kHz beep at the start of every second, to measure delay
Pink noise	Steady noise across all frequencies
A media file	An audio file, or the sound of a video, from your media library, on repeat
Your microphone	This browser’s microphone, live, for as long as you keep it on

Click the card to turn whatever plays off. Choosing another source stops the one before, including your microphone in another tab. Your microphone asks for the browser’s permission the first time and stops when you close the session page.

The card is there only on devices whose microphone can be replaced: redroid sessions on Android 11 and later. Phones keep their own microphone (and Holtdroid denies it to the app under test, see Phones).

Media library

Files you add to the library belong to you, not to a session, so every session can play them. The library also holds the images and videos the camera shows. Anything ffmpeg reads works: MP3, AAC, Opus, WAV, FLAC, or a video, whose sound is played. Files keep their format; nothing is converted on upload, and the sound is resampled to what the app records at.

Each user has media.quota (5 GiB by default; per role and per user in the users auth mode, see Authentication), and one file can be up to media.maxFileSize (1 GiB). Files stay until you delete them.

How it works

The agent starts a small helper on the device that registers an Android audio policy: every recording is routed to a remote submix that the helper plays into. The agent feeds it with ffmpeg (test signals and files, in real time) or with the samples your browser sends over a WebSocket (16-bit mono at 48 kHz, about 100 KB/s). When the helper exits, Android drops the policy and the microphone is silent again.

Configuration

media:
  enabled: true # the library and its API; on by default
  quota: 5GiB # per user; 0 = no limit
  maxFileSize: 1GiB # largest file
  storage: # optional: where files go; default is the shared storage under media/
    type: s3
    s3: { endpoint: https://s3.example.com, bucket: holtdroid, prefix: media }

Test signals and your microphone work with the library turned off.