alsa.c

#include <stdio.h>
#include <stdlib.h>
#include <mpg123.h>
#include <alsa/asoundlib.h>

#define PCM_DEVICE "default"

int main(int argc, char *argv[]) {
    if (argc < 2) {
        printf("Usage: %s <mp3 file>\n", argv[0]);
        return 1;
    }

    const char *filename = argv[1];

    // Initialize the MPG123 library
    mpg123_init();
    mpg123_handle *mh = mpg123_new(NULL, NULL);
    if (mpg123_open(mh, filename) != MPG123_OK) {
        fprintf(stderr, "Error opening %s: %s\n", filename, mpg123_strerror(mh));
        return 1;
    }

    // Retrieve the format of the MP3 file
    long rate;
    int channels, encoding;
    if (mpg123_getformat(mh, &rate, &channels, &encoding) != MPG123_OK) {
        fprintf(stderr, "Error getting format: %s\n", mpg123_strerror(mh));
        return 1;
    }

    // Set the output format
    snd_pcm_t *pcm_handle;
    snd_pcm_hw_params_t *params;
    int pcm;
    snd_pcm_uframes_t frames;
    char *buffer;
    int size;

    // Open the PCM device
    if ((pcm = snd_pcm_open(&pcm_handle, PCM_DEVICE, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
        fprintf(stderr, "Error opening PCM device %s: %s\n", PCM_DEVICE, snd_strerror(pcm));
        return 1;
    }

    // Allocate hardware parameters object
    snd_pcm_hw_params_alloca(&params);
    snd_pcm_hw_params_any(pcm_handle, params);

    // Set the desired hardware parameters
    snd_pcm_hw_params_set_access(pcm_handle, params, SND_PCM_ACCESS_RW_INTERLEAVED);
    snd_pcm_hw_params_set_format(pcm_handle, params, SND_PCM_FORMAT_S16_LE);
    snd_pcm_hw_params_set_channels(pcm_handle, params, channels);
    snd_pcm_hw_params_set_rate_near(pcm_handle, params, &rate, 0);

    // Write the parameters to the driver
    if ((pcm = snd_pcm_hw_params(pcm_handle, params)) < 0) {
        fprintf(stderr, "Error setting HW params: %s\n", snd_strerror(pcm));
        return 1;
    }

    // Decode and play the MP3 file
    size_t buffer_size = mpg123_outblock(mh);
    unsigned char *mpg123_buffer = (unsigned char *) malloc(buffer_size * sizeof(unsigned char));
    size_t done;
    int err;

    while ((err = mpg123_read(mh, mpg123_buffer, buffer_size, &done)) == MPG123_OK) {
        // Convert the mpg123_buffer to the correct format and copy to the buffer
        memcpy(buffer, mpg123_buffer, done);
        snd_pcm_writei(pcm_handle, buffer, done / (channels * 2)); // 2 bytes/sample
    }

    // Clean up
    free(buffer);
    free(mpg123_buffer);
    snd_pcm_drain(pcm_handle);
    snd_pcm_close(pcm_handle);
    mpg123_close(mh);
    mpg123_delete(mh);
    mpg123_exit();

    return 0;
}

alsa.zig

const std = @import("std");
const c = @cImport({
    @cInclude("mpg123.h");
    @cInclude("alsa/asoundlib.h");
});

pub fn brr(allocator: std.mem.Allocator, file: []const u8) !void {
    _ = c.mpg123_init();
    const handle = c.mpg123_new(null, null) orelse {
        std.log.warn("Failed to create mpg123 handle\n", .{});
        return;
    };

    const file_path: [*c]const u8 = @ptrCast(file);
    if (c.mpg123_open(handle, file_path) != c.MPG123_OK) {
        std.log.warn("Failed to open the file: {s}\n", .{file_path});
        return;
    }

    var encoding: c_int = 0;
    var channels: c_int = 0;
    var rate: c_long = 0;
    if (c.mpg123_getformat(handle, &rate, &channels, &encoding) != c.MPG123_OK) {
        std.log.warn("Failed to get format\n", .{});
        return;
    }

    var pcm: ?*c.snd_pcm_t = undefined;
    if (c.snd_pcm_open(&pcm, "default", c.SND_PCM_STREAM_PLAYBACK, 0) < 0) {
        std.log.warn("Failed to open ALSA device\n", .{});
        return;
    }

    var dir: c_int = 0;
    var params: ?*c.snd_pcm_hw_params_t = null;
    if (c.snd_pcm_hw_params_malloc(&params) < 0) {
        std.log.warn("Failed to allocate ALSA hardware parameters\n", .{});
        return;
    }

    _ = c.snd_pcm_hw_params_any(pcm, params);
    _ = c.snd_pcm_hw_params(pcm, params);
    _ = c.snd_pcm_hw_params_set_access(pcm, params, c.SND_PCM_ACCESS_RW_INTERLEAVED);
    _ = c.snd_pcm_hw_params_set_format(pcm, params, c.SND_PCM_FORMAT_S16_LE);
    _ = c.snd_pcm_hw_params_set_channels(pcm, params, @as(c_uint, @intCast(channels)));
    _ = c.snd_pcm_hw_params_set_rate_near(pcm, params, @as(*c_uint, @ptrCast(&rate)), &dir);
    if (c.snd_pcm_hw_params(pcm, params) < 0) {
        std.log.warn("Failed to set ALSA hardware parameters\n", .{});
        return;
    }

    const buffer_size = c.mpg123_outblock(handle);
    var done: usize = 0;

    var mpg123_buffer: []u8 = try allocator.alloc(u8, buffer_size);
    _ = &mpg123_buffer;
    defer allocator.free(mpg123_buffer);

    while (c.mpg123_read(handle, @as(?*anyopaque, @ptrCast(mpg123_buffer.ptr)), buffer_size, &done) == c.MPG123_OK) {
        _ = c.snd_pcm_writei(pcm, @as(?*anyopaque, @ptrCast(mpg123_buffer.ptr)), done / 4);
    }
    _ = c.mpg123_delete(handle);
    _ = c.snd_pcm_hw_params_free(params);
    _ = c.snd_pcm_close(pcm);
    _ = c.mpg123_exit();
}