feat: mp3 decoder wip

Cargo.toml

@@ -7,6 +7,7 @@ version = "0.0.0"
 crate-type = ["cdylib"]
 
 [dependencies]
+minimp3-sys = "0.3.2"
 napi = { git = "https://github.com/napi-rs/napi-rs", default-features = false, features = [
     "napi4",
 ] }

index.js

@@ -136,7 +136,7 @@ function readMetadata(result) {
     return res;
 }
 
-const { CodecType, probe, probeSync, OpusEncoder, getOpusVersion } = binding;
+const { CodecType, probe, probeSync, OpusEncoder, getOpusVersion, Mp3Decoder } = binding;
 const { version } = require('./package.json');
 
 module.exports = {
@@ -147,5 +147,6 @@ module.exports = {
     readMetadata,
     OpusEncoder,
     getOpusVersion,
+    Mp3Decoder,
     version
 };

js-binding.d.ts

@@ -94,6 +94,15 @@ export interface MetadataField {
 }
 export function probe(data: Buffer): Promise<ProbeResult>
 export function probeSync(data: Buffer): ProbeResult
+export interface Mp3DecodedFrame {
+  frameBytes: number
+  frameOffset: number
+  channels: number
+  hz: number
+  layer: number
+  bitrateKbps: number
+  data: Buffer
+}
 export type JsOpusEncoder = OpusEncoder
 export class OpusEncoder {
   constructor(sampleRate: number, channels: number)
@@ -105,3 +114,7 @@ export class OpusEncoder {
   applyDecoderCtl(request: number, value: number): void
   get version(): string
 }
+export class Mp3Decoder {
+  constructor()
+  decode(data: Buffer): Mp3DecodedFrame
+}

js-binding.js

@@ -252,10 +252,11 @@ if (!nativeBinding) {
   throw new Error(`Failed to load native binding`)
 }
 
-const { getOpusVersion, OpusEncoder, CodecType, probe, probeSync } = nativeBinding
+const { getOpusVersion, OpusEncoder, CodecType, probe, probeSync, Mp3Decoder } = nativeBinding
 
 module.exports.getOpusVersion = getOpusVersion
 module.exports.OpusEncoder = OpusEncoder
 module.exports.CodecType = CodecType
 module.exports.probe = probe
 module.exports.probeSync = probeSync
+module.exports.Mp3Decoder = Mp3Decoder

src/decoder/mod.rs

@@ -0,0 +1 @@
+mod mp3;

src/decoder/mp3/mod.rs

@@ -0,0 +1,68 @@
+use minimp3_sys::{mp3d_sample_t, mp3dec_frame_info_t};
+use minimp3_sys::{mp3dec_decode_frame, mp3dec_init, mp3dec_t, MINIMP3_MAX_SAMPLES_PER_FRAME};
+use napi::bindgen_prelude::*;
+use napi::Error;
+use napi::Result;
+use std::mem;
+
+#[napi(object)]
+pub struct Mp3DecodedFrame {
+  pub frame_bytes: i32,
+  pub frame_offset: i32,
+  pub channels: i32,
+  pub hz: i32,
+  pub layer: i32,
+  pub bitrate_kbps: i32,
+  pub data: Buffer,
+}
+
+#[napi]
+pub struct Mp3Decoder {
+  decoder: mp3dec_t,
+}
+
+#[napi]
+impl Mp3Decoder {
+  #[napi(constructor)]
+  pub fn new() -> Self {
+    let mut context = unsafe { mem::zeroed() };
+    unsafe { mp3dec_init(&mut context) };
+
+    Self { decoder: context }
+  }
+
+  #[napi]
+  pub fn decode(&mut self, data: Buffer) -> Result<Mp3DecodedFrame> {
+    let mut frame_info: mp3dec_frame_info_t = unsafe { mem::zeroed() };
+    let buffer = data.as_ref();
+    let input_len = buffer.len();
+    let mut pcm = Vec::with_capacity(MINIMP3_MAX_SAMPLES_PER_FRAME as usize);
+    let samples: usize = unsafe {
+      mp3dec_decode_frame(
+        &mut self.decoder,
+        buffer.as_ptr(),
+        input_len as _,
+        pcm.as_mut_ptr(),
+        &mut frame_info,
+      ) as _
+    };
+
+    if samples > 0 {
+      unsafe {
+        pcm.set_len(samples * frame_info.channels as usize);
+      }
+    }
+
+    let out_vec = unsafe { std::mem::transmute::<&mut [i16], &mut [u8]>(&mut pcm.as_mut()) };
+
+    Ok(Mp3DecodedFrame {
+      frame_bytes: frame_info.frame_bytes,
+      frame_offset: frame_info.frame_offset,
+      channels: frame_info.channels,
+      hz: frame_info.hz,
+      layer: frame_info.layer,
+      bitrate_kbps: frame_info.bitrate_kbps,
+      data: out_vec.to_vec().into(),
+    })
+  }
+}

src/lib.rs

@@ -4,7 +4,6 @@
 #[macro_use]
 extern crate napi_derive;
 
-// mod dasp;
-// mod decoder;
 mod opus;
 mod probe;
+mod decoder;