日本語版: README.ja.md

Optional G.722 wideband (HD voice) codec add-on for PCMFlow, aimed at real-time two-way voice over packet radio / network — VoIP, ESP-NOW transceivers, WebSocket / UDP voice links.

G.722 carries 7 kHz audio at 16 kHz sampling using the same 64 kbps wire budget as G.711 — same packet size, twice the audio bandwidth. The codec core is the public-domain sippy/libg722 (Steve Underwood / CMU); this library wraps it behind PCMFlow's PCMSource / PCMSink interfaces.

PCMFlowG722's own code is MIT. The vendored upstream is Public Domain (Steve Underwood's contributions) + a permissive CMU notice, both MIT-compatible — see src/external/LICENSE_libg722.md.

See SPEC.md for the full specification.

What's inside

Two PCM samples map to exactly one G.722 byte. v0.1 exposes only Mode 1 / 64 kbps (the rate used by RTP payload type 9 and essentially all real deployments). Mode 2 / 3 are deferred — see SPEC §"Deferred features".

WAV-container support (WAVE_FORMAT_G722) and G.722 Appendix III/IV PLC are intentionally out of scope for v0.1.

PCMFlow codec family {#pcmflow-codec-family}

PCMFlowG722 is one member of a family of optional codec add-ons for PCMFlow. Pick whichever matches your bandwidth / footprint / quality budget:

Pick G.722 when:

• You have 64 kbps of radio / network budget to spend.
• You want HD-voice quality rather than narrowband telephony — voice intelligibility and "presence" both improve dramatically over G.711.
• A moderate codec footprint (~10 KB Flash + ~512 B RAM per direction) is fine.
• Standardised wire format and patent-free licensing matter (G.722 is an ITU-T 1988 recommendation).

Pick G.711 (PCMFlowG711) when narrowband telephony is enough and you want the smallest possible codec footprint (< 4 KB Flash).

Pick Opus (PCMFlowOpus) when you need bandwidth savings or fullband audio quality.

Headline use case — ESP-NOW HD-voice transceiver

ESP-NOW carries up to 250 byte payloads. A 20 ms G.722 voice frame at 16 kHz produces exactly 160 bytes — same as G.711, but with twice the audio bandwidth. Raw 16 kHz mono 16-bit PCM at the same 20 ms is 640 byte; G.722 compresses 4×.

#include <PCMFlow.h>
#include <PCMFlowG722.h>
#include <esp_now.h>

G722Encoder enc;
G722Decoder dec;
PCMFlow audio;

void setup() {
    audio.setOutputFormat({16000, 1, 16});
    audio.setInputSource(dec);

    dec.begin({16000, 1, 16});
    enc.begin({16000, 1, 16});

    esp_now_init();
    esp_now_register_recv_cb(onEspNowRecv);
}

// Called from the ESP-NOW recv callback: feed bytes into decoder
void onEspNowRecv(const uint8_t *mac, const uint8_t *data, int len) {
    dec.decode(data, len, /*pcm_out=*/nullptr, /*max_frames=*/0);
    // PCMFlow will pump() and play the decoded PCM on the I2S/DAC side
}

End-to-end transceiver sketch (mic ↔ ESP-NOW ↔ DAC) lives in examples/EspNowTransceiver/.

Dependencies

• PCMFlow — provides PCMSource, PCMSink, ByteStream, ByteSink, and the playback pipeline. Declared via depends=PCMFlow in library.properties.

The G.722 codec core itself is vendored under src/external/libg722/ (verbatim subset of sippy/libg722); no external library needs to be installed.

Target platforms

Same posture as PCMFlow: architectures=* in library.properties, with the same realistic constraints — 32-bit MCU with malloc, modest SRAM, ~10 KB of free flash for the codec.

Practical targets: ESP32 / ESP32-S3 / ESP32-C3 / ESP32-C6 / ESP32-P4, RP2040 / RP2350, Teensy 4.x, STM32 F4+, nRF52. AVR (Uno / Mega / Nano) is not a realistic target for G.722 — the ADPCM state plus working buffers eat too much SRAM relative to those parts' ~2 KB SRAM.

Provisional footprint (encoder + decoder): Flash ≤ 12 KB, RAM ~512 B per direction. Detailed targets live in SPEC.md §6.

License

PCMFlowG722's own code: MIT (LICENSE).

The G.722 codec core under src/external/libg722/ is a verbatim subset of sippy/libg722. Its license terms are:

• Codec implementation: Public Domain (Steve Underwood, 2005).
• 1993 CMU contribution: permissive notice with acknowledgement request.
• Sippy Software maintenance: 2-clause BSD.

All three are MIT-compatible. See src/external/LICENSE_libg722.md for the verbatim upstream notices. No additional user-side attribution is required beyond the standard MIT notice; the upstream notice file is shipped in src/external/ for reference and license-hygiene auditing.

Tests

cd tests
uv run --env-file .env pytest                  # host (default)
uv run --env-file .env pytest --profile=esp32  # real ESP32 hardware

See tests/README.md. Same conventions as the parent PCMFlow test suite (pytest-embedded + Arduino CLI, lang-ship:host + esp32:esp32:esp32 profiles).