132 lines
4.2 KiB
Markdown
132 lines
4.2 KiB
Markdown
# Native Sample Rate Fix
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## Issue
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When loading a 96kHz FLAC file, the server was:
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1. Resampling it down to 48kHz "for Opus compatibility"
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2. Then negotiating with client
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3. Client advertises 96kHz/24bit support
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4. Server can't match because it already downsampled to 48kHz
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5. Falls through to Opus at 48kHz
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**Result:** Hi-res 96kHz FLAC delivered as Opus 48kHz 😢
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## Root Cause: Premature Resampling
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In `internal/server/audio_source.go:91-95`:
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```go
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// If source is not 48kHz, wrap with resampler for Opus compatibility
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if source.SampleRate() != 48000 {
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log.Printf("Resampling %s from %d Hz to 48000 Hz for Opus compatibility",
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displayName, source.SampleRate())
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return NewResampledSource(source, 48000), nil
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}
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```
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This was **premature optimization** - assuming Opus would be needed before checking what the client supports!
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## Fix Applied
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### 1. Removed Auto-Resampling
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`internal/server/audio_source.go`:
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```go
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// Note: We no longer auto-resample here. Sources are kept at native sample rate.
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// If Opus encoding is needed and source isn't 48kHz, resampling happens per-client in audio engine.
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// This allows PCM clients to receive hi-res audio at native rates!
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return source, nil
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```
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### 2. Updated Format Negotiation
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`internal/server/audio_engine.go` - `negotiateCodec()`:
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**Before:** Would pick any codec without checking if it matches the source
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**After:** Prioritizes formats in this order:
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1. **PCM at native sample rate** (preserves hi-res quality)
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2. Opus only if source is 48kHz (Opus native rate)
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3. FLAC (not implemented yet)
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4. Fallback to PCM
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```go
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// Check newer support_formats array first (spec-compliant)
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// Prioritize PCM at native rate to preserve hi-res audio quality
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for _, format := range client.Capabilities.SupportFormats {
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// Check if client supports PCM at our native sample rate
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if format.Codec == "pcm" && format.SampleRate == sourceRate && format.BitDepth == DefaultBitDepth {
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return "pcm"
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}
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}
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// If no PCM match at native rate, consider compressed codecs
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for _, format := range client.Capabilities.SupportFormats {
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// Only use Opus if source is 48kHz (Opus native rate)
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// For other rates, prefer PCM to avoid resampling
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if format.Codec == "opus" && sourceRate == 48000 {
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return "opus"
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}
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}
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```
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## Expected Behavior Now
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### Test Tone (192kHz/24bit)
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- Client advertises: [192kHz/24bit PCM, ..., Opus]
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- Server has: 192kHz/24bit source
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- **Match:** PCM 192kHz/24bit ✅
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- **Delivery:** `pcm 192000Hz 2ch 24bit`
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### 96kHz FLAC
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- Client advertises: [192kHz/24bit, 176kHz/24bit, **96kHz/24bit**, ..., Opus]
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- Server has: 96kHz/24bit FLAC
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- **Match:** PCM 96kHz/24bit ✅
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- **Delivery:** `pcm 96000Hz 2ch 24bit`
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### 48kHz MP3
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- Client advertises: [..., 48kHz/16bit, Opus]
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- Server has: 48kHz/16bit MP3
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- **Match:** PCM 48kHz/16bit OR Opus 48kHz ✅
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- **Delivery:** `pcm 48000Hz 2ch 16bit` (PCM prioritized)
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### 44.1kHz MP3
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- Client advertises: [..., 44.1kHz/16bit, Opus]
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- Server has: 44.1kHz/16bit MP3
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- **Match:** PCM 44.1kHz/16bit ✅
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- **Delivery:** `pcm 44100Hz 2ch 16bit`
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## What About Opus for Non-48kHz?
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For now, Opus is **only** used if:
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1. Source is already 48kHz, AND
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2. Client advertises Opus support
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If source is non-48kHz (like 96kHz FLAC):
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- Server will ALWAYS prefer PCM at native rate
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- No resampling, preserves full hi-res quality
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- Client handles any resampling needed on their end
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**Future:** Could add per-client resampling for Opus if client specifically requests it and doesn't support native PCM rate. But for hi-res use cases, PCM is always better anyway!
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## Testing
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```bash
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# Rebuild
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go build -o resonate-server ./cmd/resonate-server
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# Test 1: 192kHz test tone (should use PCM 192kHz)
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./resonate-server -debug -no-tui
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# Test 2: 96kHz FLAC (should use PCM 96kHz, NOT resample to 48kHz)
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./resonate-server -debug -no-tui -audio ~/Downloads/Sample_BeeMoved_96kHz24bit.flac
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# Player should show:
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# - Test 1: "Stream starting: pcm 192000Hz 2ch 24bit"
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# - Test 2: "Stream starting: pcm 96000Hz 2ch 24bit"
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```
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## Benefits
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✅ Hi-res audio preserved at native sample rates
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✅ No unnecessary downsampling
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✅ PCM prioritized over lossy compression
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✅ Better sound quality for hi-res files
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✅ Still supports Opus when appropriate (48kHz sources)
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