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21-arrangement-wav-export.md

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Feature: 21 Arrangement WAV Export

Status

In Review

Goal

Render the current arrangement to a downloadable WAV file.

Context

Users eventually need a final audio file from the arrangement they build in the browser. WAV is the first export target because it can be generated directly from PCM audio without adding a codec dependency.

Export should use the audio engine's musical data and scheduling rules, not UI timers.

Scope

Included:

  • Add an export action for the current arrangement.
  • Render the full arrangement length to audio, starting at bar 1.
  • Use OfflineAudioContext or an equivalent offline audio rendering path.
  • Include arranged hybrid clips, imported audio clips, synth/sampler instruments, and mixer routing that exist at the time this feature is implemented.
  • Apply track mute, solo, volume, and master gain if mixer routing exists.
  • Encode rendered PCM to a downloadable WAV Blob.
  • Use a predictable first export format, such as stereo 44.1 kHz 16-bit PCM WAV.
  • Show export progress, busy state, and failure feedback.
  • Block export with a clear error if required sample data is unavailable.

Excluded:

  • MP3, FLAC, AAC, or compressed export.
  • Stem export.
  • Realtime recording.
  • Mastering processors such as loudness normalization or limiting.
  • Cloud upload.
  • Exporting only selected clips.
  • Background worker rendering unless needed for responsiveness.

Constraints

  • Do not rely on React timers or visual playheads for export timing.
  • Do not mutate live playback state while exporting.
  • Keep offline rendering code separate from React components.
  • Keep exported audio deterministic for the same project data and sample assets where practical.
  • Do not add an encoder dependency unless native WAV encoding is insufficient and the PR justifies the dependency.

Done when

  • A user can click export and download a WAV file.
  • The WAV duration matches the arrangement length.
  • Arranged clips render at their expected positions.
  • Missing sample data produces a clear export error.
  • Live playback can still work after export completes or fails.
  • The PR documents which instruments and clip types are included in the first export pass.

Verification

Run:

  • npm run typecheck --if-present
  • npm run lint --if-present
  • npm run test --if-present
  • npm run build --if-present

Manual check:

  • Build a short arrangement with at least one drum clip and one pitched clip.
  • Export WAV.
  • Open the WAV in a media player or DAW.
  • Confirm the file duration and clip timing are correct.
  • Confirm export failure is clear when a required imported sample is missing.

PR notes

  • Summarize the offline rendering path.
  • State the WAV format details.
  • Mention unsupported clip or instrument types, if any.