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use crate::{NextSample, Sound};
use super::Wrapper;
// Forked from https://github.com/RustAudio/rodio/blob/d5b9ae3467dab4316ee77b260a5b7432f74866b0/src/conversions/sample_rate.rs
/// Convert a Sound from one sample rate (number of samples per second) to
/// another.
pub struct SampleRateConverter<S: Sound> {
/// The from Sound we are pulling samples from.
inner: S,
/// The output sample rate in samples per second.
to_rate: u32,
/// This is not the samples per second of the output but a possibly scaled
/// down value.
to_rate_scaled: u32,
/// This is not the samples per second of inner but a possibly scaled down
/// value.
from_rate_scaled: u32,
/// One sample per channel, extracted from `inner`.
current_frame: Vec<i16>,
/// The samples right after `current_frame` (one per channel), extracted
/// from `inner`.
next_frame: Vec<i16>,
/// Position of `current_sample` modulo `from_rate_scaled`.
current_frame_pos_in_chunk: u32,
/// The position of the next sample that this sound should return, modulo
/// `to_rate_scaled`. This counter is incremented (modulo
/// `to_rate_scale`) every time the iterator returns a complete frame.
next_output_frame_pos_in_chunk: u32,
/// The buffer containing the samples waiting to be output. Never needs to
/// contain the first channels sample. The highest channel is stored
/// first for efficient Vec::pop retrieval
output_frame: Vec<i16>,
/// The channel count of inner and ourself
channel_count: u16,
/// The number of channels has changed. We need to notify the output.
/// Note that we do not need to notify the output for sample rate changes
/// because we ensure we always output the same output sample rate and
/// we always output full frames.
channel_count_changed: bool,
/// Whether the inner channel last returned Paused or Finished
inner_paused: bool,
}
impl<S> SampleRateConverter<S>
where
S: Sound,
{
/// Create a new SampleRateConverter with an output sample rate of
/// `to_rate`.
pub fn new(inner: S, to_rate: u32) -> SampleRateConverter<S> {
let channel_count = inner.channel_count();
let mut new = SampleRateConverter {
inner,
to_rate,
to_rate_scaled: 0,
from_rate_scaled: 0,
current_frame_pos_in_chunk: 0,
next_output_frame_pos_in_chunk: 0,
current_frame: Vec::new(),
next_frame: Vec::new(),
output_frame: Vec::new(),
channel_count,
channel_count_changed: false,
inner_paused: false,
};
new.init();
new
}
fn init(&mut self) {
let channel_count = self.inner.channel_count();
if self.channel_count != channel_count {
self.channel_count_changed = true;
self.channel_count = channel_count;
}
let from_rate = self.inner.sample_rate();
assert!(from_rate >= 1);
assert!(self.to_rate >= 1);
// finding greatest common divisor
let gcd = {
#[inline]
fn gcd(a: u32, b: u32) -> u32 {
if b == 0 {
a
} else {
gcd(b, a % b)
}
}
gcd(from_rate, self.to_rate)
};
// These will get filled on the first or next call to next_sample
self.current_frame = Vec::new();
self.next_frame = Vec::new();
self.to_rate_scaled = self.to_rate / gcd;
self.from_rate_scaled = from_rate / gcd;
self.current_frame_pos_in_chunk = 0;
self.next_output_frame_pos_in_chunk = 0;
self.output_frame = Vec::with_capacity(channel_count as usize - 1);
}
fn fill_frames(&mut self) -> Result<bool, crate::Error> {
let (first_samples, next_samples) = if self.from_rate_scaled == self.to_rate_scaled {
(Vec::new(), Vec::new())
} else {
let mut collect_frame = || match self.inner.next_frame() {
Ok(f) => Ok(f),
Err(special) => match special {
Ok(NextSample::Sample(_)) => unreachable!(),
Ok(NextSample::MetadataChanged) => Err(None),
Err(e) => Err(Some(e)),
Ok(NextSample::Paused) => {
self.inner_paused = true;
Ok(Vec::new())
}
Ok(NextSample::Finished) => {
self.inner_paused = false;
Ok(Vec::new())
}
},
};
let first = match collect_frame() {
Ok(o) => o,
Err(Some(e)) => return Err(e),
Err(None) => return Ok(false),
};
let next = match collect_frame() {
Ok(o) => o,
Err(Some(e)) => return Err(e),
Err(None) => return Ok(false),
};
(first, next)
};
self.current_frame = first_samples;
self.next_frame = next_samples;
Ok(true)
}
fn next_input_frame(&mut self) -> Result<bool, crate::Error> {
self.current_frame_pos_in_chunk += 1;
std::mem::swap(&mut self.current_frame, &mut self.next_frame);
self.next_frame.clear();
let specials = self.inner.append_next_frame_to(&mut self.next_frame);
match specials {
Ok(()) => (),
Err(Ok(NextSample::Sample(_))) => unreachable!(),
Err(Ok(NextSample::MetadataChanged)) => {
return Ok(false);
}
// We handle not having any more samples left outside this function
Err(Ok(NextSample::Paused)) => self.inner_paused = true,
Err(Ok(NextSample::Finished)) => self.inner_paused = false,
Err(Err(e)) => return Err(e),
}
Ok(true)
}
/// Unwrap the inner Sound.
///
/// It is guaranteed that the inner Sound is at the start of a Frame.
/// (i.e. the inner sound has not been partially incremented inside a frame)
pub fn into_inner(self) -> S {
self.inner
}
}
impl<S> Sound for SampleRateConverter<S>
where
S: Sound,
{
fn channel_count(&self) -> u16 {
self.inner.channel_count()
}
fn sample_rate(&self) -> u32 {
self.to_rate
}
fn next_sample(&mut self) -> Result<NextSample, crate::Error> {
if self.channel_count_changed {
self.channel_count_changed = false;
return Ok(NextSample::MetadataChanged);
}
// the algorithm below doesn't work if `self.from_rate_scaled ==
// self.to_rate_scaled`
if self.from_rate_scaled == self.to_rate_scaled {
debug_assert_eq!(self.from_rate_scaled, 1);
let next = self.inner.next_sample()?;
match next {
NextSample::Sample(_) | NextSample::Paused | NextSample::Finished => {
return Ok(next);
}
NextSample::MetadataChanged => {
if self.inner.sample_rate() != self.to_rate {
self.init();
}
return Ok(NextSample::MetadataChanged);
}
}
}
// Short circuit if there are some samples waiting in the already processed
// frame
if let Some(sample) = self.output_frame.pop() {
return Ok(NextSample::Sample(sample));
}
// Coming back from being paused or first run. Refill our frames.
if self.current_frame.is_empty() && !self.fill_frames()? {
self.init();
return self.next_sample();
}
// The frame we are going to return from this function will be a linear
// interpolation between `self.current_frame` and `self.next_frame`.
if self.next_output_frame_pos_in_chunk == self.to_rate_scaled {
// If we jump to the next frame, we reset the whole state.
self.next_output_frame_pos_in_chunk = 0;
if !self.next_input_frame()? {
self.init();
return self.next_sample();
}
while self.current_frame_pos_in_chunk != self.from_rate_scaled {
if !self.next_input_frame()? {
self.init();
return self.next_sample();
}
}
self.current_frame_pos_in_chunk = 0;
} else {
// Finding the position of the first sample of the linear interpolation.
let req_left_sample = (self.from_rate_scaled * self.next_output_frame_pos_in_chunk
/ self.to_rate_scaled)
% self.from_rate_scaled;
// Advancing `self.current_frame`, `self.next_frame` and
// `self.current_frame_pos_in_chunk` until the latter variable
// matches `req_left_sample`.
while self.current_frame_pos_in_chunk != req_left_sample {
if !self.next_input_frame()? {
self.init();
return self.next_sample();
}
debug_assert!(self.current_frame_pos_in_chunk < self.from_rate_scaled);
}
}
// Merging `self.current_frame` and `self.next_frame` into `self.output_frame`.
// Note that `self.output_frame` can be truncated if there is not enough data in
// `self.next_frame`.
let mut result = None;
let numerator =
(self.from_rate_scaled * self.next_output_frame_pos_in_chunk) % self.to_rate_scaled;
// If we are coming back from a pause where the next frame was empty,
// lets fill both frames
if self.current_frame.is_empty() && !self.next_frame.is_empty() {
let has_next = self.next_input_frame()?;
if !has_next {
self.init();
return self.next_sample();
}
}
for (index, (cur, next)) in self
.current_frame
.iter()
.zip(self.next_frame.iter())
.enumerate()
// push frames in reverse for efficient retrieval
.rev()
{
let sample = linear_interpolation(*cur, *next, numerator, self.to_rate_scaled);
if index == 0 {
result = Some(sample);
} else {
self.output_frame.push(sample);
}
}
// Incrementing the counter for the next iteration.
self.next_output_frame_pos_in_chunk += 1;
if let Some(sample) = result {
Ok(NextSample::Sample(sample))
} else {
// If there are no more samples for next_frame we still want to send
// current_frame to the output
if !self.current_frame.is_empty() {
self.current_frame.reverse();
let r = NextSample::Sample(self.current_frame.pop().unwrap());
std::mem::swap(&mut self.output_frame, &mut self.current_frame);
debug_assert!(self.current_frame.is_empty());
Ok(r)
} else {
// Set things up so we will attempt to pull for more frames again
self.current_frame_pos_in_chunk = 0;
self.next_output_frame_pos_in_chunk = 0;
if self.inner_paused {
Ok(NextSample::Paused)
} else {
Ok(NextSample::Finished)
}
}
}
}
fn on_start_of_batch(&mut self) {
self.inner.on_start_of_batch()
}
}
impl<S: Sound> Wrapper for SampleRateConverter<S> {
type Inner = S;
fn inner(&self) -> &S {
&self.inner
}
fn inner_mut(&mut self) -> &mut Self::Inner {
&mut self.inner
}
fn into_inner(self) -> S {
self.inner
}
}
fn linear_interpolation(first: i16, second: i16, numerator: u32, denominator: u32) -> i16 {
(first as i64 + (second as i64 - first as i64) * numerator as i64 / denominator as i64) as i16
}
#[cfg(test)]
#[path = "./tests/sample_rate_converter.rs"]
mod tests;