Snapcast client for the ESP32. Works on the standard ESP32, does not need versions with extra memory / PSRAM.

Supported codecs:

• PCM
• Flac
• OPUS

Opus allows for 2.5-3s buffer, Flac allows for max 660ms

I've had issues with Flac due to WiFi flakiness - GTK rekeying and channel scanning by the AP cause 1~2s drops.

Building

Note that you can download the pre-built firmware from CI.

Requirements

• Install esp-rust
• cargo install ldproxy espflash

If you want to build the opus backend, you also need:

export CC=xtensa-esp32-elf-gcc
export CXX=xtensa-esp32-elf-g++

To build the project, run make only_build

Note that mDNS (automatic discovery) is not yet implemented, so you must set the IP for the snapcast server on src/main.rs.

Flashing

Requires espflash.

You need to provide the SSID and PASS environment variables, for your wifi settings:

export SSID=<your wifi name>
export PASS=<your wifi password>

These will be embedded into the firmware file with the replacer.py script.

To flash the project into an ESP32 you can run make flashm

Hardware

I use an UDA1334A module with an ESP32-WROOM-32 (a 320KiB RAM model).

Wire the pins according to this table:

ESP	I2s board
D21	WSEL
D19	DIN
D18	BCLK
GND	GND
3v3	VIN

The specific pinout is not required, you only need pins that can output, are not bootstrap pins, and do not output garbage on boot. If you want to change the wiring, you also need to modify the i2s, dout, ws and bclk variables in main().

A pull-down resistor on WSEL makes for quiet reboots; without this, there's a lot of garbled noise until playback starts.

Recommended snapserver settings

chunk_ms = 40
buffer = 2000
codec = opus

Bandwidth

On stereo at 48KHz:

• PCM requires ~1.6Mbit/s
• Flac requires ~1Mbit/s
• Opus requires ~250Kbit/s

All of which seem perfectly fine on the ESP32.

Memory usage

Basic heap analysis:

• On startup, heap low water mark 273KiB
• After setup, heap low water mark 188KiB

Free heap space:

Buffer Duration	PCM	FLAC	OPUS
150ms	167KiB	173KiB	146KiB
500ms	93KiB	117KiB	?
700ms	31KiB*	53KiB	?
2000ms	OOM	OOM	65KiB

* Got a random OOM a few times

TODO

[ ] Host a page with esp tools to provide easy flashing/firmware building