3b85604b41
PRD-local-recording.md: Dual-path architecture for podcast-quality interviews — local lossless WAV recording alongside live call, with sync markers for post-session alignment, resumable upload to a self-hosted mixer service that produces normalized multi-track output. PRD-studio-quality.md: Documents the Opus 32k/48k/64k studio tiers, when to use them, cross-codec interop, and backward compatibility. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
57 lines
2.5 KiB
Markdown
57 lines
2.5 KiB
Markdown
# PRD: Studio Quality Tiers (Opus 32k/48k/64k)
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## Status: Implemented
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Studio quality tiers have been added to the wire protocol and all clients.
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## What Was Added
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### Wire Protocol (codec_id.rs)
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Three new `CodecId` variants using the 4-bit header space (values 6-8):
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| CodecId | Wire Value | Bitrate | Frame | Use Case |
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|---------|-----------|---------|-------|----------|
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| Opus32k | 6 | 32 kbps | 20ms | Studio low — noticeable improvement over 24k for voice |
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| Opus48k | 7 | 48 kbps | 20ms | Studio — excellent voice, captures nuance |
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| Opus64k | 8 | 64 kbps | 20ms | Studio high — near-transparent quality |
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### Quality Profiles
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| Profile | Codec | FEC | Bandwidth (with FEC) |
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|---------|-------|-----|---------------------|
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| STUDIO_32K | Opus 32k | 10% | ~35 kbps |
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| STUDIO_48K | Opus 48k | 10% | ~53 kbps |
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| STUDIO_64K | Opus 64k | 10% | ~70 kbps |
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FEC is set to 10% (vs 20% for GOOD) — studio assumes a good network.
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### Client Support
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| Client | Selection | Status |
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|--------|-----------|--------|
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| Desktop (Tauri) | Quality slider in Settings (8 levels) | Done |
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| CLI | `--profile studio-64k` / `studio-48k` / `studio-32k` | Done |
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| Android | Needs codec picker update in SettingsScreen.kt | TODO |
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| Web | Needs UI | TODO |
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### Cross-Codec Interop
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All decoder auto-switch paths (call.rs, desktop engine.rs) handle the new codec IDs. A studio-64k client can talk to a codec2-1200 client — the receiver auto-switches.
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## When to Use Studio Tiers
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- **Podcast recording sessions**: Use studio-64k for best quality (combined with local WAV recording for pristine output)
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- **Music collaboration**: Opus at 48-64k captures instrument harmonics much better than 24k
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- **Good network conditions**: Only useful when bandwidth isn't constrained; the extra bits are wasted on lossy networks
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## When NOT to Use
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- **Mobile data**: Stick with Auto/GOOD — studio tiers use 2-3x the bandwidth
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- **High packet loss**: Studio profiles use minimal FEC (10%); degraded networks need DEGRADED or CATASTROPHIC profiles with 50-100% FEC
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- **Large group calls**: Each participant's stream multiplies bandwidth; 64k * 10 participants = 640 kbps incoming
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## Backward Compatibility
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Old clients (before this change) will receive packets with CodecId 6/7/8 which they don't recognize. The `from_wire()` returns `None` for unknown values, causing the packet to be dropped. Old clients can still *send* to new clients fine (they use CodecId 0-5). This is acceptable for a pre-release protocol.
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