servo_media_audio/
analyser_node.rs

1/* This Source Code Form is subject to the terms of the Mozilla Public
2 * License, v. 2.0. If a copy of the MPL was not distributed with this
3 * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
4
5use std::cmp;
6use std::f32::consts::PI;
7use std::sync::{Arc, OnceLock};
8
9use malloc_size_of_derive::MallocSizeOf;
10use servo_base::generic_channel::GenericCallback;
11
12use crate::audio_node::{
13    AudioNodeEngine, AudioNodeType, BlockInfo, ChannelInfo, ChannelInterpretation,
14};
15use crate::block::{Block, Chunk, FRAMES_PER_BLOCK_USIZE};
16
17#[derive(AudioNodeCommon)]
18pub(crate) struct AnalyserNode {
19    channel_info: ChannelInfo,
20    callback: Arc<OnceLock<GenericCallback<Block>>>,
21}
22
23impl AnalyserNode {
24    pub fn new(callback: Arc<OnceLock<GenericCallback<Block>>>, channel_info: ChannelInfo) -> Self {
25        Self {
26            callback,
27            channel_info,
28        }
29    }
30}
31
32impl AudioNodeEngine for AnalyserNode {
33    fn node_type(&self) -> AudioNodeType {
34        AudioNodeType::AnalyserNode
35    }
36
37    fn process(&mut self, inputs: Chunk, _: &BlockInfo) -> Chunk {
38        debug_assert!(inputs.len() == 1);
39
40        let mut push = inputs.blocks[0].clone();
41        push.mix(1, ChannelInterpretation::Speakers);
42
43        if let Some(callback) = self.callback.get() {
44            let _ = callback.send(push);
45        }
46
47        // analyser node doesn't modify the inputs
48        inputs
49    }
50}
51
52/// From <https://webaudio.github.io/web-audio-api/#dom-analysernode-fftsize>
53pub const MAX_FFT_SIZE: usize = 32768;
54pub const MAX_BLOCK_COUNT: usize = MAX_FFT_SIZE / FRAMES_PER_BLOCK_USIZE;
55
56/// The actual analysis is done on the DOM side. We provide
57/// the actual base functionality in this struct, so the DOM
58/// just has to do basic shimming
59#[derive(MallocSizeOf)]
60pub struct AnalysisEngine {
61    /// The number of past sample-frames to consider in the FFT
62    fft_size: usize,
63    smoothing_constant: f64,
64    min_decibels: f64,
65    max_decibels: f64,
66    /// This is a ring buffer containing the last MAX_FFT_SIZE
67    /// sample-frames
68    data: Box<[f32; MAX_FFT_SIZE]>,
69    /// The index of the current block
70    current_block: usize,
71    /// Have we computed the FFT already?
72    fft_computed: bool,
73    /// Cached blackman window data
74    blackman_windows: Vec<f32>,
75    /// The smoothed FFT data (in frequency domain)
76    smoothed_fft_data: Vec<f32>,
77    /// The computed FFT data, in decibels
78    computed_fft_data: Vec<f32>,
79    /// The windowed time domain data
80    /// Used during FFT computation
81    windowed: Vec<f32>,
82}
83
84impl AnalysisEngine {
85    pub fn new(
86        fft_size: usize,
87        smoothing_constant: f64,
88        min_decibels: f64,
89        max_decibels: f64,
90    ) -> Self {
91        debug_assert!((32..=32768).contains(&fft_size));
92        // must be a power of two
93        debug_assert!(fft_size & (fft_size - 1) == 0);
94        debug_assert!((0. ..=1.).contains(&smoothing_constant));
95        debug_assert!(max_decibels > min_decibels);
96        Self {
97            fft_size,
98            smoothing_constant,
99            min_decibels,
100            max_decibels,
101            data: Box::new([0.; MAX_FFT_SIZE]),
102            current_block: MAX_BLOCK_COUNT - 1,
103            fft_computed: false,
104            blackman_windows: Vec::with_capacity(fft_size),
105            computed_fft_data: Vec::with_capacity(fft_size / 2),
106            smoothed_fft_data: Vec::with_capacity(fft_size / 2),
107            windowed: Vec::with_capacity(fft_size),
108        }
109    }
110
111    pub fn set_fft_size(&mut self, fft_size: usize) {
112        debug_assert!((32..=32768).contains(&fft_size));
113        // must be a power of two
114        debug_assert!(fft_size & (fft_size - 1) == 0);
115        self.fft_size = fft_size;
116        self.fft_computed = false;
117    }
118
119    pub fn get_fft_size(&self) -> usize {
120        self.fft_size
121    }
122
123    pub fn set_smoothing_constant(&mut self, smoothing_constant: f64) {
124        debug_assert!((0. ..=1.).contains(&smoothing_constant));
125        self.smoothing_constant = smoothing_constant;
126        self.fft_computed = false;
127    }
128
129    pub fn get_smoothing_constant(&self) -> f64 {
130        self.smoothing_constant
131    }
132
133    pub fn set_min_decibels(&mut self, min_decibels: f64) {
134        debug_assert!(min_decibels < self.max_decibels);
135        self.min_decibels = min_decibels;
136    }
137
138    pub fn get_min_decibels(&self) -> f64 {
139        self.min_decibels
140    }
141
142    pub fn set_max_decibels(&mut self, max_decibels: f64) {
143        debug_assert!(self.min_decibels < max_decibels);
144        self.max_decibels = max_decibels;
145    }
146
147    pub fn get_max_decibels(&self) -> f64 {
148        self.max_decibels
149    }
150
151    fn advance(&mut self) {
152        self.current_block += 1;
153        if self.current_block >= MAX_BLOCK_COUNT {
154            self.current_block = 0;
155        }
156    }
157
158    /// Get the data of the current block
159    fn curent_block_mut(&mut self) -> &mut [f32] {
160        let index = FRAMES_PER_BLOCK_USIZE * self.current_block;
161        &mut self.data[index..(index + FRAMES_PER_BLOCK_USIZE)]
162    }
163
164    /// Given an index from 0 to fft_size, convert it into an index into
165    /// the backing array
166    fn convert_index(&self, index: usize) -> usize {
167        let offset = self.fft_size - index;
168        let last_element = (1 + self.current_block) * FRAMES_PER_BLOCK_USIZE - 1;
169        if offset > last_element {
170            MAX_FFT_SIZE - offset + last_element
171        } else {
172            last_element - offset
173        }
174    }
175
176    /// Given an index into the backing array, increment it
177    fn advance_index(&self, index: &mut usize) {
178        *index += 1;
179        if *index >= MAX_FFT_SIZE {
180            *index = 0;
181        }
182    }
183
184    pub fn push(&mut self, mut block: Block) {
185        debug_assert!(block.chan_count() == 1);
186        self.advance();
187        if !block.is_silence() {
188            self.curent_block_mut().copy_from_slice(block.data_mut());
189        }
190        self.fft_computed = false;
191    }
192
193    /// <https://webaudio.github.io/web-audio-api/#blackman-window>
194    fn compute_blackman_windows(&mut self) {
195        if self.blackman_windows.len() == self.fft_size {
196            return;
197        }
198        const ALPHA: f32 = 0.16;
199        const ALPHA_0: f32 = (1. - ALPHA) / 2.;
200        const ALPHA_1: f32 = 1. / 2.;
201        const ALPHA_2: f32 = ALPHA / 2.;
202        self.blackman_windows.resize(self.fft_size, 0.);
203        let coeff = PI * 2. / self.fft_size as f32;
204        for n in 0..self.fft_size {
205            self.blackman_windows[n] = ALPHA_0 - ALPHA_1 * (coeff * n as f32).cos() +
206                ALPHA_2 * (2. * coeff * n as f32).cos();
207        }
208    }
209
210    fn apply_blackman_window(&mut self) {
211        self.compute_blackman_windows();
212        self.windowed.resize(self.fft_size, 0.);
213
214        let mut data_idx = self.convert_index(0);
215        for n in 0..self.fft_size {
216            self.windowed[n] = self.blackman_windows[n] * self.data[data_idx];
217            self.advance_index(&mut data_idx);
218        }
219    }
220
221    fn compute_fft(&mut self) {
222        if self.fft_computed {
223            return;
224        }
225        self.fft_computed = true;
226        self.apply_blackman_window();
227        self.computed_fft_data.resize(self.fft_size / 2, 0.);
228        self.smoothed_fft_data.resize(self.fft_size / 2, 0.);
229
230        for k in 0..(self.fft_size / 2) {
231            let mut sum_real = 0.;
232            let mut sum_imaginary = 0.;
233            let factor = -2. * PI * k as f32 / self.fft_size as f32;
234            for n in 0..(self.fft_size) {
235                sum_real += self.windowed[n] * (factor * n as f32).cos();
236                sum_imaginary += self.windowed[n] * (factor * n as f32).sin();
237            }
238            let sum_real = sum_real / self.fft_size as f32;
239            let sum_imaginary = sum_imaginary / self.fft_size as f32;
240            let magnitude = (sum_real * sum_real + sum_imaginary * sum_imaginary).sqrt();
241            self.smoothed_fft_data[k] = (self.smoothing_constant * self.smoothed_fft_data[k] as f64 +
242                (1. - self.smoothing_constant) * magnitude as f64)
243                as f32;
244            self.computed_fft_data[k] = 20. * self.smoothed_fft_data[k].log(10.);
245        }
246    }
247
248    pub fn fill_time_domain_data(&self, dest: &mut [f32]) {
249        let mut data_idx = self.convert_index(0);
250        let end = cmp::min(self.fft_size, dest.len());
251        for entry in &mut dest[0..end] {
252            *entry = self.data[data_idx];
253            self.advance_index(&mut data_idx);
254        }
255    }
256
257    pub fn fill_byte_time_domain_data(&self, dest: &mut [u8]) {
258        let mut data_idx = self.convert_index(0);
259        let end = cmp::min(self.fft_size, dest.len());
260        for entry in &mut dest[0..end] {
261            let result = 128. * (1. + self.data[data_idx]);
262            *entry = clamp_255(result);
263            self.advance_index(&mut data_idx)
264        }
265    }
266
267    pub fn fill_frequency_data(&mut self, dest: &mut [f32]) {
268        self.compute_fft();
269        let len = cmp::min(dest.len(), self.computed_fft_data.len());
270        dest[0..len].copy_from_slice(&self.computed_fft_data[0..len]);
271    }
272
273    pub fn fill_byte_frequency_data(&mut self, dest: &mut [u8]) {
274        self.compute_fft();
275        let len = cmp::min(dest.len(), self.computed_fft_data.len());
276        let ratio = 255. / (self.max_decibels - self.min_decibels);
277        for (index, freq) in dest[0..len].iter_mut().enumerate() {
278            let result = ratio * (self.computed_fft_data[index] as f64 - self.min_decibels);
279            *freq = clamp_255(result as f32);
280        }
281    }
282}
283
284fn clamp_255(val: f32) -> u8 {
285    if val > 255. {
286        255
287    } else if val < 0. {
288        0
289    } else {
290        val as u8
291    }
292}
servo_media_audio/analyser_node.rs

servo_media_audio/
analyser_node.rs
