Expose per-player SlimProto sync tuning parameters for Squeezelite groups

[papadopouloskyriakos]

Problem

I run a fleet of 7 Squeezelite speakers (RPi Zero 2 W + DigiAMP+/HiFiBerry DAC+) in a whole-house synchronized group. With Lyrion Music Server (LMS), they play in perfect sync. I tried migrating to Music Assistant but could not achieve stable synchronized playback despite extensive configuration attempts.

The core issue: MA's Squeezelite provider hardcodes sync parameters that LMS exposes as per-player settings. Without these, it's not possible to tune for different hardware chains, WiFi conditions, and room placements.

What LMS exposes that MA doesn't

Parameter	LMS	MA (current)	Why it matters
minSyncAdjust	Per-player, user-configurable (ms)	Hardcoded MIN_DEVIATION_ADJUST = 8ms	Controls how aggressively sync corrections happen. 8ms is too tight for WiFi speakers in different rooms — causes constant micro-corrections and audio artifacts. 30ms is inaudible across rooms.
playDelay	Per-player, 0-10000ms	CONF_SYNC_ADJUST (-500 to +500ms)	One of my speakers is a Sonos Play:5 where the RPi feeds line-in via DAC → analog → Play:5 amp. This adds ~2000ms latency that needs per-player compensation. The current ±500ms range is insufficient.
bufferSecs	Global, user-configurable	Hardcoded thresholds (marked # TEMP in source)	With 7 WiFi players, the weakest link determines group stability. 3s buffer fails on marginal WiFi (-65 dBm); 5s eliminates mid-playback dropouts at the cost of ~2s play/skip latency.
bufferThreshold	Per-player, 0-255	Hardcoded in aioslimproto	Controls how full the buffer must be before playback starts. Critical for synchronized start across players with different network conditions.
maxBitrate	Per-player (0 = unlimited)	Fixed 96kHz/24-bit for groups	LMS can send native FLAC (987 kbps) directly to speakers that decode it locally at ~2% CPU. Useful for heterogeneous fleets where some players are more capable.

My setup

• 7x RPi Zero 2 W running piCorePlayer + Squeezelite
• 6x IQaudIO DigiAMP+ (TAS5756M), 1x HiFiBerry DAC+ (PCM5102A) feeding Sonos Play:5 line-in
• All on 2.4 GHz WiFi, signal ranging from -36 dBm to -65 dBm
• Synchronized as a single group playing to all rooms simultaneously
• GPIO physical buttons for play/pause/volume on 4 speakers

Proposed solution

1. Expose minSyncAdjust as a per-player setting (or at minimum a global setting) — integer, milliseconds, default 10, range 1-100
2. Extend CONF_SYNC_ADJUST range from ±500ms to at least ±5000ms for hardware chains with significant analog delay
3. Expose buffer tuning — either bufferSecs (simple) or threshold/output_threshold (advanced) as user-configurable settings
4. Optional: per-player max bitrate — allow native codec passthrough vs forced transcoding per player

There's precedent: the AirPlay provider got configurable latency in PR #3210. The Squeezelite provider would benefit from the same treatment.

Workaround

Currently using Lyrion Music Server directly for player management and sync. MA could potentially coexist as a music source provider feeding into LMS, but a native solution would be preferable.