Glossary

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Terms, domain nouns, and abbreviations used in ESP-GMF code and documentation, listed in alphabetical order.

A2DP

Advanced Audio Distribution Profile

Classic Bluetooth audio transport protocol for bidirectional audio streams.

Acquire-Release

Data access protocol for data ports

The read side calls acquire_in to obtain a payload, then release_in to return it. The write side calls acquire_out to obtain an empty payload, then release_out to submit it downstream.

AEC

Acoustic Echo Cancellation

Removes the loudspeaker output component from the microphone signal.

AFE

Audio Front-End

A set of algorithms that process raw microphone data, including AEC, NS, VAD, and WakeNet modules.

ALC

Automatic Level Control

Adjusts gain independently per channel.

AVRCP

Audio/Video Remote Control Profile

Used for playback control, metadata, and notifications.

BMGR / Board Manager

Board Manager

A YAML-based board hardware configuration system (esp_board_manager); a code generator translates the YAML into C initialization code.

Cache

Byte cache

esp_gmf_cache provides a byte-level sliding buffer that accumulates bytes from multiple payloads into a contiguous cache, then reads them back in arbitrary lengths. Commonly used by decoders to parse protocol or frame headers.

Capability

Capability descriptor

The mechanism by which an element declares its capabilities externally. Each capability descriptor node uses an EIGHTCC to identify the capability category and can carry performance information and attribute ranges, which the pool, pipeline, or application queries to select an element.

Data Bus

Data bus

The data queue underlying a port, providing four implementations: ringbuffer, fifo, block, and pbuf, responsible for cross-thread synchronization and buffering.

DRC

Dynamic Range Control

Compresses the signal according to a knee curve.

EIGHTCC

Eight Character Code

An 8-character algorithm category identifier defined in esp_gmf_caps_def.h, describing the algorithm type of an element (e.g., AUDDEC / AUDEQ).

Element

Processing unit

The processing unit in ESP-GMF, corresponding to one specific algorithm. Each element implements three fixed lifecycle functions: open / process / close.

EQ

Equalizer

Adjusts frequency response by band.

FourCC

Four Character Code

A 32-bit identifier using 4 ASCII characters to represent an encoding or container format, defined in esp_fourcc.h.

GMF

General Multimedia Framework

A lightweight general-purpose software framework built by Espressif for IoT multimedia applications.

GOP

Group of Pictures

The number of frames between two I-frames in video encoding.

HFP

Hands-Free Profile

Classic Bluetooth hands-free calling protocol.

IO

External interface

Special elements at the head or tail of a pipeline that connect to external data sources or sinks, implemented based on esp_gmf_io_t for file, HTTP, flash, codec, and I2S read/write capabilities.

is_done

End-of-stream flag (esp_gmf_payload_t field)

Set to 1 when the source IO reaches the end of its data; downstream elements process it in turn, triggering close at each stage.

Job

Work unit

The specific work unit scheduled by a task, registered in the task’s job list according to the element’s open / process / close phases. Can be marked for single or unlimited execution.

Job Stack

Job stack

The structure inside a task that stores jobs temporarily suspended by TRUNCATE. After downstream consumers process data, the task can return to the suspended job and continue execution.

MBC

Multi-Band Compressor

Compresses each frequency band independently.

Method

Runtime method

A runtime control action exposed by an element outside of open / process / close, described by esp_gmf_method_t with method name, execution function, and parameter description. Applications can call methods by name to adjust parameters such as volume, target sample rate, or target resolution.

NS

Noise Suppression

A sub-module within AFE.

OAL

Operating System Abstraction Layer

Encapsulates memory, mutex, thread, and system statistics interfaces related to the operating system and ESP-IDF.

Payload

Payload

The data carrier (esp_gmf_payload_t) flowing between elements, containing a data buffer, valid length, end-of-stream flag, timestamp, and other fields.

Pipeline

Pipeline

The orchestrator of a processing chain, connecting multiple elements in sequence and exposing run / stop / pause / resume / reset / seek control interfaces.

Pool

Pool

A template registry for elements and IO components (esp_gmf_pool_t), used to instantiate pipelines by name.

Port

Port

The data read/write interface exposed by an element, using the acquire-release protocol to access payloads. The underlying data queue is provided by a data bus.

PPA

Pixel Processing Accelerator

A hardware acceleration unit on ESP32-P4/ESP32-S3, supporting color conversion, scaling, rotation, and cropping.

PTS

Presentation Time Stamp

Used for audio/video synchronization.

QP

Quantization Parameter

The quantization parameter in video encoding, affecting compression ratio and image quality.

SE

Speech Enhancement

A sub-module within AFE.

Task

Task

A FreeRTOS thread encapsulated by the framework, running in esp_gmf_task.c, executing jobs one by one.

URL Score

URL scoring mechanism

The IO selection mechanism. Each IO implements a get_score callback to evaluate URL match quality; the pool selects the IO with the highest score.

VAD

Voice Activity Detection

Determines whether the current frame contains speech.

VCMD

Voice Command Detection

Recognizes preset command phrases based on the MultiNet model.

WWE / WakeNet

Wake Word Engine

Detects a specific wake word to trigger device activation.

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