Format Negotiation Fix

Issue

User reported seeing "Format: pcm 48000Hz Stereo 16-bit" instead of the expected "Format: pcm 192000Hz Stereo 24-bit" when connecting to the server.

Root Cause

The server's negotiateCodec() function was only checking for codec type (pcm/opus/flac) but not matching the sample rate and bit depth from the client's advertised SupportFormats array.

Previous Behavior

// Only checked codec type, ignored format details
for _, format := range client.Capabilities.SupportFormats {
    if format.Codec == "opus" {
        return "opus"
    }
    // ...
}

This meant:

Server would pick "pcm" codec
But then use its own DefaultSampleRate and DefaultBitDepth
Never checked if client actually supports those values
Could result in format mismatch

Fix Applied

Updated negotiateCodec() to check full format specification:

// Check newer support_formats array first (spec-compliant)
// Pick first format that matches what we can provide
for _, format := range client.Capabilities.SupportFormats {
    // Check if we can provide this format
    if format.Codec == "pcm" && format.SampleRate == e.source.SampleRate() && format.BitDepth == DefaultBitDepth {
        return "pcm"
    }
    // ... opus/flac checks
}

How It Works Now

Server iterates through client's SupportFormats (in order of preference)
For PCM, checks if server can provide the exact sample rate AND bit depth
Returns "pcm" codec only if there's a full format match
Falls back to opus/flac if no PCM match
Final fallback to "pcm" if no codecs match

Client Advertisement (Already Correct)

The player was already advertising correctly:

SupportFormats: []protocol.AudioFormat{
    {Codec: "pcm", Channels: 2, SampleRate: 192000, BitDepth: 24},  // First!
    {Codec: "pcm", Channels: 2, SampleRate: 176400, BitDepth: 24},
    {Codec: "pcm", Channels: 2, SampleRate: 96000, BitDepth: 24},
    {Codec: "pcm", Channels: 2, SampleRate: 88200, BitDepth: 24},
    {Codec: "pcm", Channels: 2, SampleRate: 48000, BitDepth: 16},
    {Codec: "pcm", Channels: 2, SampleRate: 44100, BitDepth: 16},
    {Codec: "opus", Channels: 2, SampleRate: 48000, BitDepth: 16},
}

Expected Result

With test tone source (192kHz/24-bit):

Client advertises: [192kHz/24bit, 176.4kHz/24bit, 96kHz/24bit, ..., 48kHz/16bit]
Server has: 192kHz/24bit source
Match found: First format (192kHz/24bit PCM)
Client receives: stream/start with 192kHz/24bit

Improved Logging

Added detailed format logging:

Audio engine: added client Mac with codec pcm (format: 192000Hz/24bit/2ch)

Testing

To verify fix works:

Stop any running server/player processes
Rebuild server: go build -o resonate-server ./cmd/resonate-server
Start server: ./resonate-server -debug
Start player: ./resonate-player -stream-logs
Check player log for: Stream starting: pcm 192000Hz 2ch 24bit
Check server log for: Audio engine: added client ... (format: 192000Hz/24bit/2ch)

Potential Issues Debugged

If still seeing 48kHz/16-bit:

Check you're using the NEW binaries (rebuild both)
Check server logs show "192000Hz/24bit" in format line
If connected to Music Assistant instead of our server, it may only support 48kHz/16bit
Check player capabilities are being sent correctly (enable debug logging)

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