beat_detector/

lib.rs

/*
MIT License

Copyright (c) 2021 Philipp Schuster

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
*/

#![deny(
clippy::all,
clippy::cargo,
clippy::nursery,
// clippy::restriction,
// clippy::pedantic
)]
// now allow a few rules which are denied by the above statement
// --> they are ridiculous and not necessary
#![allow(
    clippy::suboptimal_flops,
    clippy::redundant_pub_crate,
    clippy::fallible_impl_from
)]
#![deny(missing_debug_implementations)]
#![deny(rustdoc::all)]

use crate::strategies::lpf::LpfBeatDetector;
use crate::strategies::spectrum::SABeatDetector;
use crate::strategies::window_stats::WindowStats;
use crate::strategies::AnalysisState;

pub mod record;
mod strategies;

/// Struct that holds information about a detected beat.
#[derive(Debug)]
pub struct BeatInfo {
    relative_ms: u32,
    // todo intensity
}
impl BeatInfo {
    #[inline(always)]
    pub const fn new(relative_ms: u32) -> Self {
        Self { relative_ms }
    }

    #[inline(always)]
    pub const fn relative_ms(&self) -> u32 {
        self.relative_ms
    }
}

/// Common abstraction over a beat detection strategy. Each strategy keeps ongoing
/// audio samples, for example from microphone. Strategies should have an internal
/// mutable state via interior mutability to compare sample windows (and analysis)
/// against previous values.
pub trait Strategy {
    /// Checks if inside the samples window a new beat was recognized.
    /// If so, it returns `Some` with [`BeatInfo`] as payload.
    ///
    /// Implementations may buffer previous samples and combine them with the latest,
    /// i.e. make a sliding window.
    fn is_beat(&self, samples: &[i16]) -> Option<BeatInfo>;

    /// Convenient getter to get the [`StrategyKind`] of a strategy.
    /// This is a 1:1 mapping.
    fn kind(&self) -> StrategyKind;

    /// A nice name for the algorithm, displayable in user interfaces.
    // "where Self: Sized" => compiler gave me this hint
    // => prevents "`Strategy` cannot be made into an object"
    fn name() -> &'static str
    where
        Self: Sized;

    /// A textual description of the algorithm to help the user to select
    /// the right one.
    // "where Self: Sized" => compiler gave me this hint
    // => prevents "`Strategy` cannot be made into an object"
    fn description() -> &'static str
    where
        Self: Sized;

    /// Duration in ms after each beat. Useful do prevent the same beat to be
    /// detected as two beats. This is a constant per strategy, because more
    /// advanced strategies can cope with small durations (50ms) whereas
    /// "stupid"/basic strategies may need 400ms.
    /// This is a function instead of an associated constant, because
    /// otherwise the build fails with "`Strategy` cannot be made into an object"
    // "where Self: Sized" => compiler gave me this hint
    // => prevents "`Strategy` cannot be made into an object"
    fn min_duration_between_beats_ms() -> u32
    where
        Self: Sized;

    /// Common implementation for all strategies which checks if
    /// the last beat is beyond the threshold. Of not, we can return early
    /// and do not need to check if a beat is in the given sample.
    #[inline(always)]
    fn last_beat_beyond_threshold(&self, state: &AnalysisState) -> bool
    where
        Self: Sized,
    {
        // only check this if at least a single beat was recognized
        if state.beat_time_ms() > 0 {
            let threshold = state.last_beat_timestamp() + Self::min_duration_between_beats_ms();
            if state.beat_time_ms() < threshold {
                return false;
            }
        }
        true
    }

    /// Common implementation for all strategies which checks if
    /// the current windows/frames max amplitude (i16) is above a value where
    /// a beat could happen in theory (discard noise/silence/break between songs)
    #[inline(always)]
    fn amplitude_high_enough(&self, w_stats: &WindowStats) -> bool {
        const MIN_AMPLITUDE_THRESHOLD: i16 = (i16::MAX as f32 * 0.3) as i16;
        w_stats.max() >= MIN_AMPLITUDE_THRESHOLD as u16
    }
}

/// Enum that conveniently and easily makes all [`Strategy`]s provided by this crate accessible.
/// This enum provides the bare minimum functionality to access the strategies. All deeper
/// functionality must be defined inside the implementations.
#[derive(Debug, PartialEq, Eq, Hash)]
#[non_exhaustive] // more will come in the future
pub enum StrategyKind {
    /// Corresponds to [`strategies::lpf::LpfBeatDetector`].
    LPF,
    /// Corresponds to [`strategies::spectrum::SABeatDetector`]
    Spectrum,
}

impl StrategyKind {
    /// Creates a concrete detector object, i.e. a struct that implements
    /// [`Strategy`] on that you can continuously analyze your input audio data.
    #[inline(always)]
    fn detector(&self, sampling_rate: u32) -> Box<dyn Strategy + Send> {
        match self {
            StrategyKind::LPF => Box::new(LpfBeatDetector::new(sampling_rate)),
            StrategyKind::Spectrum => Box::new(SABeatDetector::new(sampling_rate)),
            // _ => panic!("Unknown Strategy"),
        }
    }

    /// Convenient wrapper for ['Strategy::name'].
    pub fn name(&self) -> &'static str {
        match self {
            StrategyKind::LPF => LpfBeatDetector::name(),
            StrategyKind::Spectrum => SABeatDetector::name(),
            // _ => panic!("Unknown Strategy"),
        }
    }

    /// Convenient wrapper for ['Strategy::description'].
    pub fn description(&self) -> &'static str {
        match self {
            StrategyKind::LPF => LpfBeatDetector::description(),
            StrategyKind::Spectrum => SABeatDetector::description(),
            // _ => panic!("Unknown Strategy"),
        }
    }

    /// Returns a vector with all strategy kinds to iterate over them.
    pub fn values() -> Vec<Self> {
        vec![Self::LPF, Self::Spectrum]
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use minimp3::{Decoder as Mp3Decoder, Error as Mp3Error, Frame as Mp3Frame};
    use std::collections::HashMap;
    use std::fs::File;

    // opened the file in Audacity and looked where the
    // beats are
    const SAMPLE_1_EXPECTED_BEATS_MS: [u32; 6] = [300, 2131, 2297, 4303, 6143, 6310];

    #[test]
    fn test_sample_1_print_beats() {
        let (sample_1_audio_data, sampling_rate) = read_mp3_to_mono("res/sample_1.mp3");
        // assert 44,1kHz because it makes things easier
        assert_eq!(
            sampling_rate, 44100,
            "The sampling rate of the MP3 examples must be 44100Hz."
        );

        // 1/44100 * 1024 == 1024/44100 == 0.046439s == 23,2ms
        let window_length = 1024;

        let map =
            apply_samples_to_all_strategies(window_length, &sample_1_audio_data, sampling_rate);

        for (strategy, beats) in map {
            println!("Strategy {:?} found beats at:", strategy);
            for beat in beats {
                println!("  {}ms", beat.relative_ms());
            }
        }
    }

    /// TODO this test only works for a "pretty good" beat detection algorithm, because
    ///  beats are close together. This doesn't work for the two existing ones.
    ///  Make this test more tolerant, i.e. only for the "good algorithms" that
    ///  hopefully come in the future.
    #[test]
    #[ignore]
    fn test_sample_1_beat_detection() {
        let (sample_1_audio_data, sampling_rate) = read_mp3_to_mono("res/sample_1.mp3");
        // assert 44,1kHz because it makes things easier
        assert_eq!(
            sampling_rate, 44100,
            "The sampling rate of the MP3 examples must be 44100Hz."
        );

        // 1/44100 * 1024 == 1024/44100 == 0.046439s == 23,2ms
        let window_length = 1024;

        let map =
            apply_samples_to_all_strategies(window_length, &sample_1_audio_data, sampling_rate);

        const DIFF_WARN_MS: u32 = 30;
        const DIFF_ERROR_MS: u32 = 60;

        for (strategy, beats) in map {
            assert_eq!(
                SAMPLE_1_EXPECTED_BEATS_MS.len(),
                beats.len(),
                "Strategy {:?} must detect {} beats in sample 1!",
                strategy,
                SAMPLE_1_EXPECTED_BEATS_MS.len()
            );
            for (i, beat) in beats.iter().enumerate() {
                let abs_diff =
                    (SAMPLE_1_EXPECTED_BEATS_MS[i] as i64 - beat.relative_ms() as i64).abs() as u32;
                assert!(abs_diff < DIFF_ERROR_MS, "[{:?}]: Recognized beat[{}] should not be more than {} ms away from the actual value; is {}ms", strategy, i, DIFF_ERROR_MS, abs_diff);
                if abs_diff >= DIFF_WARN_MS {
                    eprintln!("[{:?}]: WARN: Recognized beat[{}] should is less than {}ms away from the actual value; is: {}ms", strategy, i, DIFF_WARN_MS, abs_diff);
                };
            }
        }
    }

    fn apply_samples_to_all_strategies(
        window_length: usize,
        samples: &[i16],
        _sampling_rate: u32,
    ) -> HashMap<StrategyKind, Vec<BeatInfo>> {
        // we pad with zeroes until the audio data length is a multiple
        // of the window length
        let mut samples = Vec::from(samples);
        let remainder = samples.len() % window_length;
        if remainder != 0 {
            samples.extend_from_slice(&vec![0; remainder])
        }

        let window_count = samples.len() / window_length;

        // all strategies
        let strategies = vec![StrategyKind::LPF, StrategyKind::Spectrum];

        let mut map = HashMap::new();

        for strategy in strategies {
            let detector = strategy.detector(44100);
            let mut beats = Vec::new();
            for i in 0..window_count {
                let window = &samples[i * window_length..(i + 1) * window_length];
                let beat = detector.is_beat(window);
                if let Some(beat) = beat {
                    beats.push(beat);
                }
            }
            map.insert(strategy, beats);
        }

        map
    }

    /// Reads an MP3 and returns the audio data as mono channel + the sampling rate in Hertz.
    fn read_mp3_to_mono(file: &str) -> (Vec<i16>, u32) {
        let mut decoder = Mp3Decoder::new(File::open(file).unwrap());

        let mut sampling_rate = 0;
        let mut mono_samples = vec![];
        loop {
            match decoder.next_frame() {
                Ok(Mp3Frame {
                    data: samples_of_frame,
                    sample_rate,
                    channels,
                    ..
                }) => {
                    // that's a bird weird of the original API. Why should channels or sampling
                    // rate change from frame to frame?

                    // Should be constant throughout the MP3 file.
                    sampling_rate = sample_rate;

                    if channels == 2 {
                        for (i, sample) in samples_of_frame.iter().enumerate().step_by(2) {
                            let sample = *sample as i32;
                            let next_sample = samples_of_frame[i + 1] as i32;
                            mono_samples.push(((sample + next_sample) as f32 / 2.0) as i16);
                        }
                    } else if channels == 1 {
                        mono_samples.extend_from_slice(&samples_of_frame);
                    } else {
                        panic!("Unsupported number of channels={}", channels);
                    }
                }
                Err(Mp3Error::Eof) => break,
                Err(e) => panic!("{:?}", e),
            }
        }

        (mono_samples, sampling_rate as u32)
    }
}