Audio Processing Guide

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Complete reference for GPU-accelerated audio operations in ExCubecl.

AudioSamples Struct

%ExCubecl.AudioSamples{
  handle:      #Reference<...>,   # GPU buffer (f32 planar PCM)
  channels:    2,
  sample_rate: 48000,
  frames:      1024,              # samples per channel
  pts:         0                 # presentation timestamp (µs)
}

Mixing

# Simple mix (equal gain)
{:ok, mixed} = ExCubecl.Audio.mix([track_a, track_b])

# Mix with per-track gain
{:ok, mixed} = ExCubecl.Audio.mix([track_a, track_b], gains: [0.7, 0.5])

# Mix many tracks
{:ok, mixed} = ExCubecl.Audio.mix(
  [dialogue, music, sfx],
  gains: [1.0, 0.3, 0.6]
)

The pcm_mix kernel sums N tracks with per-channel gain on the GPU.

Overlay with Ducking

# Overlay foreground on background, ducking background by 12dB
{:ok, mixed} = ExCubecl.Audio.overlay(bg, fg, duck_level: -12)

# Custom duck level
{:ok, mixed} = ExCubecl.Audio.overlay(bg, fg, duck_level: -6)

Resampling

# 44.1kHz → 48kHz
{:ok, resampled} = ExCubecl.Audio.resample(samples, from: 44100, to: 48000)

# 48kHz → 44.1kHz
{:ok, resampled} = ExCubecl.Audio.resample(samples, from: 48000, to: 44100)

Uses GPU-accelerated linear interpolation. For higher quality, use the biquad_filter kernel for band-limited resampling.

Channel Conversion

# Stereo → Mono (downmix)
{:ok, mono} = ExCubecl.Audio.channels(samples, :stereo, :mono)

# Mono → Stereo (upmix)
{:ok, stereo} = ExCubecl.Audio.channels(mono_samples, :mono, :stereo)

# Supported layouts: :mono, :stereo, :surround_51, :surround_71

GPU Audio Filters

# EQ (via biquad filter)
{:ok, eq'd} = ExCubecl.Filter.apply(samples, :eq,
  bands: [{:high_pass, 80}, {:shelf_high, 8000, 3.0}])

# Compressor
{:ok, compressed} = ExCubecl.Filter.apply(samples, :compressor,
  threshold: -18, ratio: 4.0)

# Reverb (FFT convolution)
{:ok, reverbed} = ExCubecl.Filter.apply(samples, :reverb,
  room_size: 0.5, wet: 0.2)

# Normalize
{:ok, normalized} = ExCubecl.Filter.apply(samples, :normalize)

Audio Filter Chains

{:ok, result} = ExCubecl.Filter.chain(samples, [
  {:eq, [bands: [{:high_pass, 80}]]},
  {:compressor, [threshold: -18, ratio: 4.0]},
  {:normalize, []}
])

Pipeline Integration

ExCubecl.pipeline()
|> ExCubecl.pipeline_add(%{op: :read_frame, source: src})
|> ExCubecl.pipeline_add(%{op: :filter, kernel: :pcm_mix, params: %{gains: [0.7, 0.5]}})
|> ExCubecl.pipeline_add(%{op: :filter, kernel: :biquad_filter, params: %{bands: [{:high_pass, 80}]}})
|> ExCubecl.pipeline_add(%{op: :encode, encoder: enc})
|> ExCubecl.pipeline_run()