1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109

use std::time::Duration;

use crate::{Sample, Source};

use super::SeekError;

/// Internal function that builds a `Speed` object.
pub fn speed<I>(input: I, factor: f32) -> Speed<I> {
    Speed { input, factor }
}

/// Filter that modifies each sample by a given value.
#[derive(Clone, Debug)]
pub struct Speed<I> {
    input: I,
    factor: f32,
}

impl<I> Speed<I>
where
    I: Source,
    I::Item: Sample,
{
    /// Modifies the speed factor.
    #[inline]
    pub fn set_factor(&mut self, factor: f32) {
        self.factor = factor;
    }

    /// Returns a reference to the inner source.
    #[inline]
    pub fn inner(&self) -> &I {
        &self.input
    }

    /// Returns a mutable reference to the inner source.
    #[inline]
    pub fn inner_mut(&mut self) -> &mut I {
        &mut self.input
    }

    /// Returns the inner source.
    #[inline]
    pub fn into_inner(self) -> I {
        self.input
    }
}

impl<I> Iterator for Speed<I>
where
    I: Source,
    I::Item: Sample,
{
    type Item = I::Item;

    #[inline]
    fn next(&mut self) -> Option<I::Item> {
        self.input.next()
    }

    #[inline]
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.input.size_hint()
    }
}

impl<I> ExactSizeIterator for Speed<I>
where
    I: Source + ExactSizeIterator,
    I::Item: Sample,
{
}

impl<I> Source for Speed<I>
where
    I: Source,
    I::Item: Sample,
{
    #[inline]
    fn current_frame_len(&self) -> Option<usize> {
        self.input.current_frame_len()
    }

    #[inline]
    fn channels(&self) -> u16 {
        self.input.channels()
    }

    #[inline]
    fn sample_rate(&self) -> u32 {
        (self.input.sample_rate() as f32 * self.factor) as u32
    }

    #[inline]
    fn total_duration(&self) -> Option<Duration> {
        self.input.total_duration().map(|d| d.mul_f32(self.factor))
    }

    #[inline]
    fn try_seek(&mut self, pos: Duration) -> Result<(), SeekError> {
        /* TODO: This might be wrong, I do not know how speed achieves its speedup
         * so I can not reason about the correctness.
         * <dvdsk noreply@davidsk.dev> */

        // even after 24 hours of playback f32 has enough precision
        let pos_accounting_for_speedup = pos.mul_f32(self.factor);
        self.input.try_seek(pos_accounting_for_speedup)
    }
}