sfxmix-audio-processing

SfxMix Audio Processing

Instructions

Preserve Audio Quality

Keep intermediate processing lossless. Pipeline steps should write temporary audio as WAV PCM unless the user is explicitly exporting to a compressed final format such as MP3 or OGG.

Compression belongs at the final save() boundary. Do not add MP3 encoding inside actions such as concat, mix, silence generation, filters, trim, or chunk splitting.

Match the Fluent API

Public methods should be chainable and return this. Add work to this.actions, then implement the actual processing in _processActions().

Use domain names that describe the audio behavior. For silence-detected sound segments, use chunk terminology:

sfx
    .add('input.wav')
    .split({ chunk: 1 })
    .save('second_chunk.wav');

split() Defaults

The default chunk splitting options are:

{
    chunk: 0,
    threshold: -35,
    silenceDuration: 0.03,
    paddingStart: 0,
    paddingEnd: 30,
    minDuration: 0.01
}

chunk is zero-based. chunk: 0 keeps the first detected non-silent segment; chunk: 1 keeps the second.

Function Reference

Use README.md as the user-facing source for API examples and docs. When changing a public method or filter, keep this reference, README.md, and index.js aligned.

Public API

• constructor(config = {}): Initializes an action queue, current file state, output bitrate, and a unique temp directory. config.bitrate defaults to 64000; use null to let FFmpeg choose. config.tmpDir overrides the OS temp base.
• add(input): Queues an audio file for concatenation. Returns this.
• mix(input, options = {}): Queues a mix against the current audio. If called first, it behaves like add(input). options.duration supports 'longest', 'shortest', or 'first'; default is 'longest'. Returns this.
• silence(milliseconds): Queues generated silence in milliseconds. Returns this.
• filter(filterName, options = {}): Queues a named FFmpeg audio filter. Returns this.
• trim(options = {}): Queues leading/trailing silence trimming while preserving internal silence. Defaults: startDuration: 0, startThreshold: -30, stopDuration: 0.05, stopThreshold: -30, paddingStart: 0, paddingEnd: 0. Returns this.
• split(options = {}): Queues extraction of one silence-detected non-silent chunk. Defaults are listed above. Returns this.
• normalize(tp = -1.5): Convenience wrapper for filter('normalize', { tp }). Returns this.
• save(output, outputOptions = {}): Processes queued actions, writes the final output, resets the instance, and resolves with the absolute output path. Custom outputOptions are passed to convertAudio().
• isTruncated(options = {}): Terminal analysis operation. Processes queued actions, checks whether the audio tail is above options.threshold, resets the instance, and resolves { truncated, tailRmsDb, tailPeakDb, duration, threshold, tailDuration }. Defaults: tailDuration: 50, threshold: -30.
• reset(): Clears queued actions and current file state. Returns this.

Conversion Helpers

• convertAudio(inputFile, outputFile, outputOptions = {}): Converts audio to the requested output path. Without custom options, chooses codec/format from the extension: OGG/Opus, WAV/PCM, FLAC, AAC/M4A, or MP3/libmp3lame.
• convertToOgg(inputFile, outputFile, options = {}): Backward-compatible alias for convertAudio().

Supported Filters

• normalize: EBU R128 loudness normalization. Options: i, lra, tp.
• telephone: High-pass plus low-pass telephone effect. Options: lowFreq, highFreq.
• echo: FFmpeg aecho. Options: inGain, outGain, delays, decays.
• highpass: Requires frequency.
• lowpass: Requires frequency.
• volume: Requires volume.
• equalizer: Requires frequency, width, and gain.
• flanger: Options: delay, depth, regen, width, speed, shape, phase, interp.
• pitch: Requires pitch in semitones.
• tremolo: Options: frequency.
• phaser: Options: in_gain, out_gain, delay, decay, speed, type.
• tempo: Requires x. Values outside FFmpeg's single-filter 0.5 to 2.0 range are split into chained atempo filters.

Internal Processing Helpers

• getTempFile(prefix, extension = 'wav'): Builds unique temp file paths inside the instance temp directory.
• applyIntermediateOutput(command, outputFile): Forces intermediate FFmpeg output to WAV PCM.
• cleanup(): Removes the instance temp directory.
• _processActions(): Runs queued add, mix, silence, filter, trim, and split actions in order.
• safeDeleteFile(filePath, maxRetries = 3): Deletes temp files with retry backoff.
• isTempFile(filename): Checks whether a path belongs to the instance temp directory.
• concatenateAudioFiles(inputFiles, outputFile): Concatenates files with FFmpeg's concat filter.
• mixAudioFiles(inputFile1, inputFile2, outputFile, options = {}): Mixes two inputs with FFmpeg's amix.
• _analyzeTail(filePath, options = {}): Reads the tail as PCM samples and computes RMS/peak dB metrics.
• getAudioInfo(inputFile): Reads channel count, sample rate, and bitrate through ffprobe.
• generateSilence(durationMs, outputFile, audioInfo = null): Generates PCM silence matching provided audio metadata when available.
• applyFilter(inputFile, filterName, options, outputFile): Resolves a filter chain and writes a filtered intermediate WAV.
• applyTrim(inputFile, options, outputFile): Applies leading/trailing silence removal.
• applySplit(inputFile, options, outputFile): Detects silence boundaries and extracts the requested chunk.
• getAudioDuration(inputFile): Reads duration through ffprobe.
• parseSilenceEvent(line): Parses FFmpeg silencedetect stderr lines.
• detectSilence(inputFile, options = {}): Runs silencedetect and returns ordered silence events.
• getNonSilentSegments(silenceEvents, duration, minDuration = 0.01): Converts silence events into non-silent segments.
• getFilterChain(filterName, options): Maps supported filter names and options to FFmpeg filter strings.