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Mic Splice

Sets and Functions

  1. $P$ — the set of participants (anonymous until named).
  2. $\mathrm{track}: P \to \mathit{AudioTrack} \cup {\bot}$ — the active local audio track for each participant.
  3. $\mathrm{subscribeState}: P \to {\text{none}, \text{lowBW}}$ — each participant's subscription state (no full audio playback).
  4. $\mathrm{sessionActive} \in {\text{true}, \text{false}}$ — indicates if a recording session is currently in progress.
  5. $\mathrm{multitrackFiles} \subseteq \mathcal{P}(\mathit{AudioFile})$ — the set of finalized session recordings (each file = separate channels per participant).
  6. $\mathrm{currentRecording} \in \mathit{AudioFile} \cup {\bot}$ — the in-progress multitrack file (or $\bot$ if no active session).
  7. $\mathrm{S3Bucket}$ — the configured S3-compatible storage.
  8. $\mathrm{S3Notification}$ — mechanism that fires when new uploads appear, so the system can refresh download links.

Invariants

  1. Always No Video
    $$ \forall p \in P:\ \mathrm{track}(p).\mathrm{kind} = \text{audio-only} $$ (No participant ever establishes a video track.)

  2. No Audio Playback
    $$ \forall p \in P:\ \mathrm{subscribeState}(p) = \text{lowBW} \implies \text{audio-element is muted} $$ (Playback is always muted; only minimal "speaking indicator" subscriptions.)

  3. User-Initiated Recording

    • A recording session starts only when a participant clicks "Record."
    • The session continues until stopped or all participants leave.

  4. Unified Timeline
    $\mathrm{currentRecording}$ continues on the server even if any $p \in P$ disconnects.

  5. Finalization Required for Download
    $$ \text{Only } f \in \mathrm{multitrackFiles} \text{ (finalized) can be downloaded.} $$

  6. S3-Compatible Upload
    $$ \forall f \in \mathrm{multitrackFiles}:\ f \text{ is stored in } \mathrm{S3Bucket} $$ (Recorded files automatically upload via S3-compatible APIs.)

  7. S3 Notifications

    • Whenever the bucket changes (new file or updated file), $\mathrm{S3Notification}$ is fired, prompting the UI to fetch updated file links.

Events and Transitions

  1. Join

    • Trigger: A new participant $p$ arrives.
    • Effects:
      $$ P \leftarrow P \cup {p}; \quad \mathrm{track}(p) \leftarrow \text{new AudioTrack}(\text{defaultMic}); \quad \mathrm{subscribeState}(p) \leftarrow \text{lowBW} $$

  2. Start Recording

    • Trigger: A participant clicks "Record."
    • Effects:
      • If $\mathrm{sessionActive} = \text{true}$, finalize the current recording: $$ \mathrm{multitrackFiles} \leftarrow \mathrm{multitrackFiles} \cup {\mathrm{currentRecording}}; \quad \mathrm{currentRecording} \text{ is pushed to } \mathrm{S3Bucket} $$
      • Begin a fresh server-side recording: $$ \mathrm{sessionActive} \leftarrow \text{true}; \quad \mathrm{currentRecording} \leftarrow \text{new LiveKitRecordingHandle} $$

  3. Stop Recording

    • Trigger: A participant clicks "Stop."
    • Effects:
      $$ \mathrm{multitrackFiles} \leftarrow \mathrm{multitrackFiles} \cup {\mathrm{currentRecording}}; \quad \mathrm{currentRecording} \rightarrow \mathrm{S3Bucket}; \quad \mathrm{currentRecording} \leftarrow \bot; \quad \mathrm{sessionActive} \leftarrow \text{false} $$
    • (Files remain available for download after they have been finalized.)

  4. Download

    • Trigger: A participant requests any previously finalized file $f$.
    • Precondition: $f \in \mathrm{multitrackFiles}$.
    • Effect: Return a download link from $\mathrm{S3Bucket}$.

  5. S3 Bucket Update

    • Trigger: $\mathrm{S3Notification}$ fires when new uploads appear.
    • Effect: The UI refreshes with updated file links.

  6. Leave

    • Trigger: Participant $p$ leaves.
    • Effects:
      $$ P \leftarrow P \setminus {p}; \quad \mathrm{track}(p) \leftarrow \bot $$ If $P = \varnothing$ and $\mathrm{sessionActive} = \text{true}$, then finalize: $$ \mathrm{multitrackFiles} \leftarrow \mathrm{multitrackFiles} \cup {\mathrm{currentRecording}}; \quad \mathrm{currentRecording} \rightarrow \mathrm{S3Bucket}; \quad \mathrm{sessionActive} \leftarrow \text{false}; \quad \mathrm{currentRecording} \leftarrow \bot $$