initial (& perhaps final) commit

2 files changed, 104 insertions, 0 deletions

diff --git a/src/README.md b/src/README.md
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+++ b/src/README.md
@@ -0,0 +1 @@
+# seamless-loop
diff --git a/src/main.rs b/src/main.rs
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+++ b/src/main.rs
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+/*
+SEAMLESS LOOP
+For more information see README.md.
+---
+License:
+do what the fuck you want to
+*/
+
+use clap::Parser;
+use std::fs::File;
+use std::fmt::{Debug, Display};
+use anyhow::{Result, Context};
+
+/// Turn a .wav file into a seamless loop.
+#[derive(Parser, Debug)]
+struct Args {
+	/// Input file
+	file: String,
+	
+	/// Output file. Defaults to "x-seamless.wav" for input file "x.wav".
+	#[arg(short)]
+	output: Option<String>,
+	
+	/// Duration in seconds of the fade.
+	#[arg(short, default_value_t = 0.03)]
+	duration: f32,
+}
+
+trait AudioSample: Copy + Debug + Display {
+	fn interpolate(self, other: Self, t: f32) -> Self;
+}
+
+macro_rules! impl_audio_sample {
+	($type:ty, $min:expr, $max:expr) => {
+		impl AudioSample for $type {
+			fn interpolate(self, other: Self, t: f32) -> Self {
+				let a = self as f32;
+				let b = other as f32;
+				(a * (1.0 - t) + b * t).clamp($min, $max) as Self
+			}
+		}
+	}
+}
+
+impl_audio_sample!(u8, 0.0, 255.0);
+impl_audio_sample!(i16, -32767.0, 32767.0);
+// NOTE: twenty-two bit samples are shifted left by 8 by the wav crate, so this is correct for them
+impl_audio_sample!(i32, -i32::MAX as f32, i32::MAX as f32);
+impl_audio_sample!(f32, -1.0, 1.0);
+
+fn make_seamless<T: AudioSample>(data: &mut Vec<T>, channels: u16, fade_samples: usize) -> Result<()> {
+	let channels: usize = channels.into();
+	let audio_samples = data.len();
+	if fade_samples * 2 >= audio_samples {
+		return Err(anyhow::anyhow!("Fade duration is too long (must be less than half of audio file's duration)."));
+	}
+	if audio_samples % channels != 0 {
+		return Err(anyhow::anyhow!("Sample count is not multiple of channel count (this shouldn't happen)."));
+	}
+	let fade_frames = fade_samples / channels;
+	let audio_frames = audio_samples / channels;
+	for i in 0..fade_frames {
+		let t = i as f32 / (fade_frames as f32);
+		let j = audio_frames - fade_frames + i;
+		for c in 0..channels {
+			data[channels * i + c] = data[channels * j + c].interpolate(data[channels * i + c], t);
+		}
+	}
+	data.truncate((audio_frames - fade_frames) * channels);
+	Ok(())
+}
+
+fn main() -> Result<()> {
+	let args = Args::parse();
+	let input = &args.file;
+	let output = args.output.unwrap_or_else(|| {
+		let name = input.strip_suffix(".wav").unwrap_or(input);
+		name.to_string() + "-seamless.wav"
+	});
+	let mut input_file = File::open(input).with_context(|| format!("Couldn't open input file {input}"))?;
+	let (header, mut data) = wav::read(&mut input_file)?;
+	drop(input_file);
+	
+	let samples = header.sampling_rate as f32 * args.duration;
+	if !samples.is_finite() || samples < 0.0 || samples > usize::MAX as f32 {
+		return Err(anyhow::anyhow!("Bad duration"));
+	}
+	let samples = samples as usize;
+	let channels = header.channel_count;
+	use wav::BitDepth;
+	match &mut data {
+		BitDepth::Eight(data) => make_seamless(data, channels, samples)?,
+		BitDepth::Sixteen(data) => make_seamless(data, channels, samples)?,
+		BitDepth::TwentyFour(data) => make_seamless(data, channels, samples)?,
+		BitDepth::ThirtyTwoFloat(data) => make_seamless(data, channels, samples)?,
+		BitDepth::Empty => return Err(anyhow::anyhow!("No audio data")),
+	}
+	
+	let mut output_file = File::create(&output).with_context(|| format!("Couldn't open output file {output}"))?;
+	wav::write(header, &data, &mut output_file)?;
+	
+	Ok(())
+}