Support writing stereo wav files.

.gitignore

@@ -16,5 +16,5 @@ Cargo.lock
 __pycache__
 
 bria.mp3
-bria.wav
+bria*.wav
 bria.opus

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "sphn"
-version = "0.1.2"
+version = "0.1.3"
 edition = "2021"
 license = "MIT/Apache-2.0"
 description = "pyo3 wrappers to read/write audio files"

src/lib.rs

@@ -172,14 +172,43 @@ fn read(
 #[pyo3(signature = (filename, data, sample_rate))]
 fn write_wav(
     filename: std::path::PathBuf,
-    data: numpy::PyReadonlyArray1<f32>,
+    data: numpy::PyReadonlyArrayDyn<f32>,
     sample_rate: u32,
 ) -> PyResult<()> {
     let w = std::fs::File::create(&filename).w_f(&filename)?;
     let mut w = std::io::BufWriter::new(w);
     let data = data.as_array();
-    let data = to_cow(&data);
-    wav::write(&mut w, &data, sample_rate).w_f(&filename)?;
+    match data.ndim() {
+        1 => {
+            let data = data.into_dimensionality::<numpy::Ix1>().w()?;
+            let data = to_cow(&data);
+            wav::write_mono(&mut w, &data, sample_rate).w_f(&filename)?;
+        }
+        2 => {
+            let data = data.into_dimensionality::<numpy::Ix2>().w()?;
+            match data.shape() {
+                [1, l] => {
+                    let data = data.into_shape((*l,)).w()?;
+                    let data = to_cow(&data);
+                    wav::write_mono(&mut w, &data, sample_rate).w_f(&filename)?;
+                }
+                [2, l] => {
+                    let data = data.into_shape((2 * *l,)).w()?;
+                    let data = to_cow(&data);
+                    let (pcm1, pcm2) = (&data[..*l], &data[*l..]);
+                    let data = pcm1
+                        .iter()
+                        .zip(pcm2.iter())
+                        .flat_map(|(s1, s2)| [*s1, *s2])
+                        .collect::<Vec<_>>();
+                    println!("{:?}", &data[..20]);
+                    wav::write_stereo(&mut w, &data, sample_rate).w_f(&filename)?
+                }
+                _ => py_bail!("expected one or two channels, got shape {:?}", data.shape()),
+            }
+        }
+        _ => py_bail!("expected one or two dimensions, got shape {:?}", data.shape()),
+    }
     Ok(())
 }
 

src/wav.rs

@@ -22,15 +22,18 @@ impl Sample for i16 {
     }
 }
 
-pub fn write<W: Write, S: Sample>(
+/// The samples are copied as is in the resulting wav files so are assumed to be interleaved by
+/// channel.
+pub fn write_multi<W: Write, S: Sample>(
     w: &mut W,
     samples: &[S],
+    n_channels: u16,
     sample_rate: u32,
 ) -> std::io::Result<()> {
+    // https://en.wikipedia.org/wiki/WAV#WAV_file_header
     let len = 12u32; // header
     let len = len + 24u32; // fmt
     let len = len + samples.len() as u32 * 2 + 8; // data
-    let n_channels = 1u16;
     let bytes_per_second = sample_rate * 2 * n_channels as u32;
     w.write_all(b"RIFF")?;
     w.write_all(&(len - 8).to_le_bytes())?; // total length minus 8 bytes
@@ -40,10 +43,10 @@ pub fn write<W: Write, S: Sample>(
     w.write_all(b"fmt ")?;
     w.write_all(&16u32.to_le_bytes())?; // block len minus 8 bytes
     w.write_all(&1u16.to_le_bytes())?; // PCM
-    w.write_all(&n_channels.to_le_bytes())?; // one channel
+    w.write_all(&n_channels.to_le_bytes())?;
     w.write_all(&sample_rate.to_le_bytes())?;
     w.write_all(&bytes_per_second.to_le_bytes())?;
-    w.write_all(&2u16.to_le_bytes())?; // 2 bytes of data per sample
+    w.write_all(&(n_channels * 2).to_le_bytes())?; // 2 bytes of data per sample and channel
     w.write_all(&16u16.to_le_bytes())?; // bits per sample
 
     // Data block
@@ -54,3 +57,19 @@ pub fn write<W: Write, S: Sample>(
     }
     Ok(())
 }
+
+pub fn write_mono<W: Write, S: Sample>(
+    w: &mut W,
+    samples: &[S],
+    sample_rate: u32,
+) -> std::io::Result<()> {
+    write_multi(w, samples, 1, sample_rate)
+}
+
+pub fn write_stereo<W: Write, S: Sample>(
+    w: &mut W,
+    samples: &[S],
+    sample_rate: u32,
+) -> std::io::Result<()> {
+    write_multi(w, samples, 2, sample_rate)
+}

test/basic.py

@@ -1,3 +1,4 @@
+import numpy as np
 import sphn
 
 filename = "bria.mp3"
@@ -13,7 +14,8 @@
 data, sr = sphn.read(filename)
 print(data.shape, sr)
 
-sphn.write_wav("bria.wav", data[0], sr)
+sphn.write_wav("bria_mono.wav", data[0], sr)
+sphn.write_wav("bria_stereo.wav", np.concatenate([data, data]), sr)
 sphn.write_opus("bria.opus", data, sr)
 
 data_roundtrip, sr_roundtrip = sphn.read_opus("bria.opus")