decoders: implement minimp3-based MP3 decoder

Closes #36.

src/decoder/mod.rs

@@ -9,6 +9,8 @@ use Source;
 
 #[cfg(feature = "flac")]
 mod flac;
+#[cfg(feature = "mp3")]
+mod mp3;
 #[cfg(feature = "vorbis")]
 mod vorbis;
 #[cfg(feature = "wav")]
@@ -17,15 +19,15 @@ mod wav;
 /// Source of audio samples from decoding a file.
 ///
 /// Supports WAV, Vorbis and Flac.
-#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis"))]
+#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3"))]
 pub struct Decoder<R>(DecoderImpl<R>)
 where
     R: Read + Seek;
 
-#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis")))]
+#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3")))]
 pub struct Decoder<R>(::std::marker::PhantomData<R>);
 
-#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis"))]
+#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3"))]
 enum DecoderImpl<R>
 where
     R: Read + Seek,
@@ -36,6 +38,8 @@ where
     Vorbis(vorbis::VorbisDecoder<R>),
     #[cfg(feature = "flac")]
     Flac(flac::FlacDecoder<R>),
+    #[cfg(feature = "mp3")]
+    Mp3(mp3::Mp3Decoder<R>),
 }
 
 impl<R> Decoder<R>
@@ -71,11 +75,19 @@ where
             },
         };
 
+        #[cfg(feature = "mp3")]
+        let data = match mp3::Mp3Decoder::new(data) {
+            Err(data) => data,
+            Ok(decoder) => {
+                return Ok(Decoder(DecoderImpl::Mp3(decoder)));
+            },
+        };
+
         Err(DecoderError::UnrecognizedFormat)
     }
 }
 
-#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis")))]
+#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3")))]
 impl<R> Iterator for Decoder<R>
 where
     R: Read + Seek,
@@ -87,7 +99,7 @@ where
     }
 }
 
-#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis"))]
+#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3"))]
 impl<R> Iterator for Decoder<R>
 where
     R: Read + Seek,
@@ -103,6 +115,8 @@ where
             DecoderImpl::Vorbis(ref mut source) => source.next(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref mut source) => source.next(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref mut source) => source.next(),
         }
     }
 
@@ -115,11 +129,13 @@ where
             DecoderImpl::Vorbis(ref source) => source.size_hint(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref source) => source.size_hint(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref source) => source.size_hint(),
         }
     }
 }
 
-#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis")))]
+#[cfg(not(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3")))]
 impl<R> Source for Decoder<R>
 where
     R: Read + Seek,
@@ -138,7 +154,7 @@ where
     }
 }
 
-#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis"))]
+#[cfg(any(feature = "wav", feature = "flac", feature = "vorbis", feature = "mp3"))]
 impl<R> Source for Decoder<R>
 where
     R: Read + Seek,
@@ -152,6 +168,8 @@ where
             DecoderImpl::Vorbis(ref source) => source.current_frame_len(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref source) => source.current_frame_len(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref source) => source.current_frame_len(),
         }
     }
 
@@ -164,6 +182,8 @@ where
             DecoderImpl::Vorbis(ref source) => source.channels(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref source) => source.channels(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref source) => source.channels(),
         }
     }
 
@@ -176,6 +196,8 @@ where
             DecoderImpl::Vorbis(ref source) => source.sample_rate(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref source) => source.sample_rate(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref source) => source.sample_rate(),
         }
     }
 
@@ -188,6 +210,8 @@ where
             DecoderImpl::Vorbis(ref source) => source.total_duration(),
             #[cfg(feature = "flac")]
             DecoderImpl::Flac(ref source) => source.total_duration(),
+            #[cfg(feature = "mp3")]
+            DecoderImpl::Mp3(ref source) => source.total_duration(),
         }
     }
 }

src/decoder/mp3.rs

@@ -0,0 +1,79 @@
+use std::io::{Read, Seek};
+use std::time::Duration;
+
+use Source;
+
+use minimp3::{Decoder, Frame};
+
+pub struct Mp3Decoder<R>
+where
+    R: Read + Seek,
+{
+    decoder: Decoder<R>,
+    current_frame: Frame,
+    current_frame_offset: usize,
+}
+
+impl<R> Mp3Decoder<R>
+where
+    R: Read + Seek,
+{
+    pub fn new(data: R) -> Result<Self, ()> {
+        let mut decoder = Decoder::new(data);
+        let current_frame = decoder.next_frame().map_err(|_| ())?;
+
+        Ok(Mp3Decoder {
+            decoder,
+            current_frame,
+            current_frame_offset: 0,
+        })
+    }
+}
+
+impl<R> Source for Mp3Decoder<R>
+where
+    R: Read + Seek
+{
+    #[inline]
+    fn current_frame_len(&self) -> Option<usize> {
+        Some(self.current_frame.data.len())
+    }
+
+    #[inline]
+    fn channels(&self) -> u16 {
+        self.current_frame.channels as _
+    }
+
+    #[inline]
+    fn sample_rate(&self) -> u32 {
+        self.current_frame.sample_rate as _
+    }
+
+    #[inline]
+    fn total_duration(&self) -> Option<Duration> {
+        None
+    }
+}
+
+impl<R> Iterator for Mp3Decoder<R>
+where
+    R: Read + Seek
+{
+    type Item = i16;
+
+    #[inline]
+    fn next(&mut self) -> Option<i16> {
+        if self.current_frame_offset == self.current_frame.data.len() {
+            self.current_frame_offset = 0;
+            match self.decoder.next_frame() {
+                Ok(frame) => self.current_frame = frame,
+                _ => return None,
+            }
+        }
+
+        let v = self.current_frame.data[self.current_frame_offset];
+        self.current_frame_offset += 1;
+
+        return Some(v);
+    }
+}