file_backend/
file_backend.rs

1//! Read a track from a file/image backing instead of a physical drive.
2//!
3//! `cd-da-reader` doesn't bake in any image format (CHD, BIN/CUE, ...). Instead
4//! you implement [`AudioSectorReader`] for your backing — supplying raw CD-DA
5//! sectors (2352 bytes/sector, 16-bit signed little-endian stereo) — and reuse
6//! the crate's TOC/track machinery via [`read_track`] and [`create_wav`].
7//!
8//! This example uses a tiny in-memory backing so it stays dependency-free. A
9//! real backing (e.g. CHD via `libchdman-rs`) would decode sectors in
10//! `read_audio_sectors` and build its TOC from the image's track metadata.
11//!
12//! Run with: `cargo run --example file_backend`
13mod common;
14
15use cd_da_reader::{
16    AudioSectorReader, Toc, Track, create_wav, lba_to_msf, open_track_stream, read_track,
17};
18
19/// A backing that holds whole-disc PCM in memory and slices it per sector.
20struct InMemoryDisc {
21    /// Whole-disc PCM, laid out as 2352 bytes per sector.
22    pcm: Vec<u8>,
23}
24
25impl AudioSectorReader for InMemoryDisc {
26    type Error = std::io::Error;
27
28    fn read_audio_sectors(&self, start_lba: u32, count: u32) -> Result<Vec<u8>, Self::Error> {
29        let start = start_lba as usize * 2352;
30        let end = start + count as usize * 2352;
31        self.pcm.get(start..end).map(<[u8]>::to_vec).ok_or_else(|| {
32            std::io::Error::new(std::io::ErrorKind::UnexpectedEof, "read past end of disc")
33        })
34    }
35}
36
37fn main() -> Result<(), Box<dyn std::error::Error>> {
38    let output_dir = common::fresh_output_dir("file_backend")?;
39
40    // A real backing derives this TOC from the image's own track metadata.
41    // Here we fabricate a 2-track disc: 2 seconds + 3 seconds of audio.
42    let track1_sectors = 75 * 2;
43    let track2_sectors = 75 * 3;
44    let total_sectors = track1_sectors + track2_sectors;
45
46    let toc = Toc {
47        first_track: 1,
48        last_track: 2,
49        tracks: vec![
50            Track {
51                number: 1,
52                start_lba: 0,
53                start_msf: lba_to_msf(0),
54                is_audio: true,
55            },
56            Track {
57                number: 2,
58                start_lba: track1_sectors,
59                start_msf: lba_to_msf(track1_sectors),
60                is_audio: true,
61            },
62        ],
63        leadout_lba: total_sectors,
64    };
65
66    // Silence, just for the demo — a real backing decodes actual audio here.
67    let disc = InMemoryDisc {
68        pcm: vec![0u8; total_sectors as usize * 2352],
69    };
70
71    for track in &toc.tracks {
72        let pcm = read_track(&disc, &toc, track.number)?;
73        println!(
74            "track {}: {} bytes ({} sectors)",
75            track.number,
76            pcm.len(),
77            pcm.len() / 2352
78        );
79
80        let wav = create_wav(pcm);
81        let output_path = output_dir.join(format!("track{:02}.wav", track.number));
82        std::fs::write(&output_path, wav)?;
83        println!("  wrote {}", output_path.display());
84    }
85
86    // The same backing can be streamed instead of buffered: pull sector-aligned
87    // chunks so a player never holds a whole track in memory at once. (A backing
88    // whose tracks are addressed contiguously — a gap-stripped extract — would
89    // open with `TrackBounds::Gapless`, or supply its own bounds via
90    // `open_track_stream_at`; this demo TOC has no trailing data track, so plain
91    // `open_track_stream` is equivalent.)
92    let mut stream = open_track_stream(&disc, &toc, 1)?;
93    let (mut chunks, mut bytes) = (0u32, 0usize);
94    while let Some(chunk) = stream.next_chunk()? {
95        chunks += 1;
96        bytes += chunk.len();
97    }
98    println!(
99        "streamed track 1: {bytes} bytes in {chunks} chunks ({:.1}s of audio)",
100        stream.total_seconds()
101    );
102
103    Ok(())
104}
file_backend/file_backend.rs

file_backend/
file_backend.rs
