docs: add casting/streaming research document
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# Casting/Streaming Research for QBZ
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## Overview
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This document outlines options for adding audio casting/streaming capabilities to QBZ, allowing users to stream music to external devices like Chromecast, DLNA receivers, AirPlay speakers, etc.
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---
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## 1. Chromecast (Google Cast)
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### The Challenge
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Google Cast protocol is proprietary and Google does not provide official SDKs for desktop Linux applications. The protocol uses:
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- mDNS for device discovery
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- CASTV2 protocol over TLS for control
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- HTTP streaming for media delivery
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### FOSS Options
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#### rust-cast
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- **Repo**: https://github.com/nicoulaj/rust-cast (archived)
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- **Status**: Archived, last updated 2020
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- **Notes**: Basic implementation but unmaintained
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#### pychromecast (Python)
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- **Repo**: https://github.com/home-assistant/pychromecast
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- **Status**: Active (used by Home Assistant)
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- **Notes**: Python library, would require FFI bridge or separate process
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- **Viability**: Good reference implementation
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#### catt (CLI tool)
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- **Repo**: https://github.com/skorokithakis/catt
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- **Status**: Active
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- **Notes**: CLI tool wrapping pychromecast, could spawn as subprocess
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- **Viability**: Quick integration via CLI, but adds Python dependency
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### Recommendation
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**Medium difficulty**. Best approach would be to either:
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1. Port pychromecast logic to Rust (significant effort)
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2. Use catt as subprocess for MVP (adds Python dependency)
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3. Wait for a maintained Rust crate to emerge
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---
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## 2. DLNA/UPnP (Digital Living Network Alliance)
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### The Protocol
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DLNA uses UPnP for device discovery and control. More open than Chromecast.
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### FOSS Options
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#### rupnp (Rust)
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- **Repo**: https://github.com/jakobhellermann/rupnp
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- **Status**: Active
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- **Features**: UPnP device discovery and control
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- **Viability**: Good foundation for DLNA support
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#### gupnp (GLib/C)
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- **Repo**: https://gitlab.gnome.org/GNOME/gupnp
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- **Status**: Active, mature
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- **Notes**: GNOME project, would need Rust bindings
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- **Viability**: Solid but requires C FFI
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#### miniupnpc (C)
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- **Status**: Active, widely used
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- **Notes**: Focused on port forwarding, less relevant for media
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### Recommendation
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**Easier than Chromecast**. `rupnp` provides a good Rust-native foundation. Would need to implement:
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1. DLNA Media Renderer discovery
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2. AVTransport service control
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3. HTTP server for streaming audio to renderer
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---
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## 3. AirPlay (Apple)
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### The Protocol
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AirPlay 1 (audio) is somewhat documented. AirPlay 2 adds features but is more complex.
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### FOSS Options
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#### shairport-sync
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- **Repo**: https://github.com/mikebrady/shairport-sync
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- **Status**: Active, excellent
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- **Notes**: AirPlay *receiver* (not sender) - opposite of what we need
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#### uxplay
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- **Repo**: https://github.com/FDH2/UxPlay
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- **Status**: Active
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- **Notes**: Also a receiver, not sender
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#### raop-player (C)
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- **Repo**: https://github.com/philippe44/raop-player
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- **Status**: Active
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- **Notes**: AirPlay sender! Can stream to AirPlay devices
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- **Viability**: Best option - would need C FFI bindings
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### Recommendation
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**Medium difficulty**. `raop-player` is the only viable sender implementation. Would require:
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1. C bindings via bindgen
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2. Integration with QBZ audio pipeline
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3. mDNS discovery for AirPlay devices
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---
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## 4. Bluetooth Audio (A2DP)
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### The Protocol
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A2DP (Advanced Audio Distribution Profile) is standard for Bluetooth audio streaming.
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### FOSS Options
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#### BlueZ + PipeWire/PulseAudio
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- **Status**: Standard Linux audio stack
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- **Notes**: Already handled at OS level
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- **Viability**: Works out of the box if user pairs device
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#### bluer (Rust)
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- **Repo**: https://github.com/bluez/bluer
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- **Status**: Active, official BlueZ Rust bindings
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- **Notes**: Could use for device discovery/management UI
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### Recommendation
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**Easiest option**. Bluetooth audio "just works" through the Linux audio stack. QBZ could:
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1. Add UI to show paired Bluetooth audio devices
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2. Use `bluer` to list/connect devices
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3. Audio routing handled by PipeWire/PulseAudio automatically
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---
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## 5. Snapcast (Multi-room Audio)
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### The Protocol
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Open source multi-room audio solution. Server-client architecture.
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### FOSS Options
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#### snapcast
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- **Repo**: https://github.com/badaix/snapcast
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- **Status**: Active
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- **Notes**: C++ server/client, could integrate as audio sink
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### Recommendation
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**Niche but interesting**. Good for users with Snapcast setup. Could be added as an audio output option.
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---
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## Implementation Priority Recommendation
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### Phase 1: Quick Wins
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1. **Bluetooth UI** - Use `bluer` to show/manage Bluetooth audio devices
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- Effort: Low
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- Value: High (most users have Bluetooth speakers)
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### Phase 2: DLNA Support
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2. **DLNA/UPnP** - Use `rupnp` for device discovery and streaming
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- Effort: Medium
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- Value: High (many receivers, smart TVs support DLNA)
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### Phase 3: Chromecast (if demand exists)
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3. **Chromecast** - Either subprocess approach or wait for better Rust support
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- Effort: High
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- Value: Medium-High (popular but complex)
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### Phase 4: AirPlay (if demand exists)
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4. **AirPlay** - FFI bindings to `raop-player`
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- Effort: Medium-High
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- Value: Medium (Apple ecosystem users)
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---
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## Architecture Considerations
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### Audio Pipeline Integration
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Current QBZ audio flow:
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```
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Qobuz API → Download → Decode (symphonia) → Rodio Sink → System Audio
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```
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For casting, we'd need:
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```
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Qobuz API → Download → Decode → [Cast Protocol] → External Device
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```
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Options:
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1. **Stream raw audio** - Send decoded PCM to cast device
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2. **Stream URL** - Give cast device the Qobuz stream URL directly (may not work due to auth)
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3. **Local HTTP server** - Transcode and serve via HTTP, give URL to cast device
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### Recommended Architecture
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```
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┌─────────────────┐
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│ Local Speaker │
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│ (Rodio) │
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└────────▲────────┘
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│
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┌──────────┐ ┌──────────┐ ┌───────────┴───────────┐
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│ Qobuz │───▶│ Decode │───▶│ Audio Router │
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│ API │ │(symphonia)│ │ │
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└──────────┘ └──────────┘ └───────────┬───────────┘
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│
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┌────────▼────────┐
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│ HTTP Server │
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│ (for casting) │
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└────────┬────────┘
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│
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┌───────────────────┼───────────────────┐
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│ │ │
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┌────▼────┐ ┌─────▼─────┐ ┌─────▼─────┐
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│ DLNA │ │Chromecast │ │ AirPlay │
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│Renderer │ │ Device │ │ Speaker │
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└─────────┘ └───────────┘ └───────────┘
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```
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---
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## Next Steps
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1. [ ] Decide on priority order based on user needs
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2. [ ] Prototype Bluetooth device UI with `bluer`
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3. [ ] Evaluate `rupnp` for DLNA implementation
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4. [ ] Research Chromecast protocol further if prioritized
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---
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## Resources
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- [UPnP Device Architecture](http://upnp.org/specs/arch/UPnP-arch-DeviceArchitecture-v1.1.pdf)
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- [DLNA Guidelines](https://spirespark.com/dlna/guidelines)
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- [Chromecast Protocol Analysis](https://github.com/nicoulaj/rust-cast/wiki)
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- [AirPlay Protocol Docs](https://nto.github.io/AirPlay.html)
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- [bluer Rust crate](https://docs.rs/bluer/latest/bluer/)
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- [rupnp Rust crate](https://docs.rs/rupnp/latest/rupnp/)
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