Ajoute une fonction de transcodage xxx-> flac en stream à pmoflac

pmoflac/src/transcode.rs

@@ -0,0 +1,394 @@
+//! High-level audio transcoding helpers.
+//!
+//! This module exposes convenience utilities to convert any format supported by
+//! `pmoflac` into a streaming FLAC pipeline. When the input is already FLAC the
+//! transcoder bypasses any re-encoding and simply forwards the original byte
+//! stream.
+
+use std::{
+    io,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use tokio::io::{AsyncRead, AsyncReadExt, BufReader, ReadBuf};
+
+use crate::{
+    autodetect::{decode_audio_stream, DecodeAudioError, DecodedAudioStream},
+    encode_flac_stream, EncoderOptions, FlacEncodedStream, FlacError, PcmFormat, StreamInfo,
+};
+
+const READ_CHUNK: usize = 4096;
+
+/// List of audio codecs supported by the transcoder.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum AudioCodec {
+    Flac,
+    Mp3,
+    OggVorbis,
+    OggOpus,
+    Wav,
+    Aiff,
+}
+
+/// Options controlling how the transcoder operates.
+#[derive(Debug, Clone)]
+pub struct TranscodeOptions {
+    /// Encoder options forwarded to the FLAC backend.
+    pub encoder_options: EncoderOptions,
+}
+
+impl Default for TranscodeOptions {
+    fn default() -> Self {
+        Self {
+            encoder_options: EncoderOptions::default(),
+        }
+    }
+}
+
+/// Stream returned by [`transcode_to_flac_stream`].
+pub struct FlacTranscodeStream {
+    inner: FlacTranscodeInner,
+}
+
+enum FlacTranscodeInner {
+    Passthrough(Pin<Box<dyn AsyncRead + Send>>),
+    Encoded(FlacEncodedStream),
+}
+
+impl FlacTranscodeStream {
+    fn passthrough<R>(reader: R) -> Self
+    where
+        R: AsyncRead + Send + 'static,
+    {
+        Self {
+            inner: FlacTranscodeInner::Passthrough(Box::pin(reader)),
+        }
+    }
+
+    fn encoded(stream: FlacEncodedStream) -> Self {
+        Self {
+            inner: FlacTranscodeInner::Encoded(stream),
+        }
+    }
+
+    /// Returns true when the input was already FLAC and no re-encoding was required.
+    pub fn is_passthrough(&self) -> bool {
+        matches!(self.inner, FlacTranscodeInner::Passthrough(_))
+    }
+
+    /// Waits for the encoding task (if any) to finish.
+    pub async fn wait(self) -> Result<(), FlacError> {
+        match self.inner {
+            FlacTranscodeInner::Passthrough(_) => Ok(()),
+            FlacTranscodeInner::Encoded(stream) => stream.wait().await,
+        }
+    }
+}
+
+impl AsyncRead for FlacTranscodeStream {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        match &mut self.as_mut().get_mut().inner {
+            FlacTranscodeInner::Passthrough(reader) => reader.as_mut().poll_read(cx, buf),
+            FlacTranscodeInner::Encoded(stream) => Pin::new(stream).poll_read(cx, buf),
+        }
+    }
+}
+
+/// Result of a successful FLAC transcoding pipeline.
+pub struct TranscodeToFlac {
+    codec: AudioCodec,
+    info: StreamInfo,
+    stream: FlacTranscodeStream,
+}
+
+impl TranscodeToFlac {
+    fn new(codec: AudioCodec, info: StreamInfo, stream: FlacTranscodeStream) -> Self {
+        Self {
+            codec,
+            info,
+            stream,
+        }
+    }
+
+    /// Returns the codec that was detected for the input stream.
+    pub fn input_codec(&self) -> AudioCodec {
+        self.codec
+    }
+
+    /// Returns the PCM characteristics (or FLAC metadata when passthrough) of the input.
+    pub fn input_stream_info(&self) -> &StreamInfo {
+        &self.info
+    }
+
+    /// Indicates whether the transcoder forwarded the original FLAC stream unchanged.
+    pub fn is_passthrough(&self) -> bool {
+        self.stream.is_passthrough()
+    }
+
+    /// Consumes the result and yields the FLAC stream.
+    pub fn into_stream(self) -> FlacTranscodeStream {
+        self.stream
+    }
+
+    /// Consumes the result and returns the associated information with the stream.
+    pub fn into_parts(self) -> (AudioCodec, StreamInfo, FlacTranscodeStream) {
+        (self.codec, self.info, self.stream)
+    }
+}
+
+/// Error type returned by [`transcode_to_flac_stream`].
+#[derive(thiserror::Error, Debug)]
+pub enum TranscodeError {
+    #[error("decode error: {0}")]
+    Decode(#[from] DecodeAudioError),
+    #[error("encode error: {0}")]
+    Encode(#[from] FlacError),
+}
+
+/// Transcodes any supported audio stream into FLAC using a fully streaming pipeline.
+///
+/// This function combines the automatic format detection logic with the streaming
+/// decoders and the FLAC encoder. The input is never fully buffered in memory:
+/// chunks are decoded and immediately re-encoded, allowing low-latency pipelines
+/// suitable for HTTP downloads or on-the-fly conversions.
+pub async fn transcode_to_flac_stream<R>(
+    reader: R,
+    options: TranscodeOptions,
+) -> Result<TranscodeToFlac, TranscodeError>
+where
+    R: AsyncRead + Unpin + Send + 'static,
+{
+    let mut reader = BufReader::new(reader);
+    let mut prefix = Vec::new();
+
+    if let Some(info) = detect_flac_passthrough(&mut reader, &mut prefix).await? {
+        let passthrough_reader = PrefixedReader::new(prefix, reader);
+        let stream = FlacTranscodeStream::passthrough(passthrough_reader);
+        return Ok(TranscodeToFlac::new(AudioCodec::Flac, info, stream));
+    }
+
+    let prefixed_reader = PrefixedReader::new(prefix, reader);
+    let decoded = decode_audio_stream(prefixed_reader).await?;
+    match decoded {
+        DecodedAudioStream::Flac(stream) => {
+            transcode_from_decoded(AudioCodec::Flac, stream, options.encoder_options).await
+        }
+        DecodedAudioStream::Mp3(stream) => {
+            transcode_from_decoded(AudioCodec::Mp3, stream, options.encoder_options).await
+        }
+        DecodedAudioStream::OggVorbis(stream) => {
+            transcode_from_decoded(AudioCodec::OggVorbis, stream, options.encoder_options).await
+        }
+        DecodedAudioStream::OggOpus(stream) => {
+            transcode_from_decoded(AudioCodec::OggOpus, stream, options.encoder_options).await
+        }
+        DecodedAudioStream::Wav(stream) => {
+            transcode_from_decoded(AudioCodec::Wav, stream, options.encoder_options).await
+        }
+        DecodedAudioStream::Aiff(stream) => {
+            transcode_from_decoded(AudioCodec::Aiff, stream, options.encoder_options).await
+        }
+    }
+}
+
+async fn transcode_from_decoded<E>(
+    codec: AudioCodec,
+    stream: crate::decoder_common::DecodedStream<E>,
+    encoder_options: EncoderOptions,
+) -> Result<TranscodeToFlac, TranscodeError>
+where
+    E: std::error::Error + From<String> + Send + 'static,
+{
+    let info = stream.info().clone();
+    let pcm_format = PcmFormat {
+        sample_rate: info.sample_rate,
+        channels: info.channels,
+        bits_per_sample: info.bits_per_sample,
+    };
+
+    let flac_stream = encode_flac_stream(stream, pcm_format, encoder_options).await?;
+    Ok(TranscodeToFlac::new(
+        codec,
+        info,
+        FlacTranscodeStream::encoded(flac_stream),
+    ))
+}
+
+async fn detect_flac_passthrough<R>(
+    reader: &mut BufReader<R>,
+    prefix: &mut Vec<u8>,
+) -> Result<Option<StreamInfo>, DecodeAudioError>
+where
+    R: AsyncRead + Unpin,
+{
+    ensure_prefix_len(reader, prefix, 4).await?;
+    if &prefix[..4] != b"fLaC" {
+        return Ok(None);
+    }
+
+    ensure_prefix_len(reader, prefix, 8).await?;
+    let block_header = &prefix[4..8];
+    let block_type = block_header[0] & 0x7F;
+    let block_len = ((block_header[1] as usize) << 16)
+        | ((block_header[2] as usize) << 8)
+        | block_header[3] as usize;
+
+    if block_type != 0 || block_len < 34 {
+        return Ok(None);
+    }
+
+    let total_len = 8 + block_len;
+    ensure_prefix_len(reader, prefix, total_len).await?;
+    let stream_info_block = &prefix[8..total_len];
+    Ok(parse_flac_stream_info(stream_info_block))
+}
+
+async fn ensure_prefix_len<R>(
+    reader: &mut BufReader<R>,
+    buf: &mut Vec<u8>,
+    target_len: usize,
+) -> Result<(), DecodeAudioError>
+where
+    R: AsyncRead + Unpin,
+{
+    let mut tmp = [0u8; READ_CHUNK];
+    while buf.len() < target_len {
+        let needed = target_len - buf.len();
+        let chunk_len = tmp.len().min(needed);
+        let read = reader
+            .read(&mut tmp[..chunk_len])
+            .await
+            .map_err(DecodeAudioError::from)?;
+        if read == 0 {
+            return Err(DecodeAudioError::UnknownFormat);
+        }
+        buf.extend_from_slice(&tmp[..read]);
+    }
+    Ok(())
+}
+
+fn parse_flac_stream_info(block: &[u8]) -> Option<StreamInfo> {
+    if block.len() < 34 {
+        return None;
+    }
+
+    let min_block_size = u16::from_be_bytes([block[0], block[1]]);
+    let max_block_size = u16::from_be_bytes([block[2], block[3]]);
+
+    let sample_rate =
+        ((block[10] as u32) << 12) | ((block[11] as u32) << 4) | ((block[12] as u32) >> 4);
+
+    let channels = ((block[12] & 0x0E) >> 1) + 1;
+    let bits_per_sample = ((((block[12] & 0x01) as u32) << 4) | ((block[13] as u32) >> 4)) + 1;
+
+    let total_samples = ((block[13] as u64 & 0x0F) << 32)
+        | ((block[14] as u64) << 24)
+        | ((block[15] as u64) << 16)
+        | ((block[16] as u64) << 8)
+        | (block[17] as u64);
+
+    Some(StreamInfo {
+        sample_rate,
+        channels,
+        bits_per_sample: bits_per_sample as u8,
+        total_samples: if total_samples == 0 {
+            None
+        } else {
+            Some(total_samples)
+        },
+        max_block_size,
+        min_block_size,
+    })
+}
+
+struct PrefixedReader<R> {
+    prefix: Vec<u8>,
+    position: usize,
+    reader: R,
+}
+
+impl<R> PrefixedReader<R> {
+    fn new(prefix: Vec<u8>, reader: R) -> Self {
+        Self {
+            prefix,
+            position: 0,
+            reader,
+        }
+    }
+}
+
+unsafe impl<R: Send> Send for PrefixedReader<R> {}
+impl<R: Unpin> Unpin for PrefixedReader<R> {}
+
+impl<R: AsyncRead + Unpin> AsyncRead for PrefixedReader<R> {
+    fn poll_read(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+        buf: &mut ReadBuf<'_>,
+    ) -> Poll<io::Result<()>> {
+        if self.position < self.prefix.len() && buf.remaining() > 0 {
+            let remaining = self.prefix.len() - self.position;
+            let to_copy = remaining.min(buf.remaining());
+            buf.put_slice(&self.prefix[self.position..self.position + to_copy]);
+            self.position += to_copy;
+            return Poll::Ready(Ok(()));
+        }
+
+        Pin::new(&mut self.reader).poll_read(cx, buf)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::io::Cursor;
+    use tokio::io::AsyncReadExt;
+
+    #[tokio::test]
+    async fn transcode_roundtrip_flac_passthrough() -> Result<(), Box<dyn std::error::Error>> {
+        let pcm_samples = vec![0i16; 44_100 * 2];
+        let pcm_bytes: Vec<u8> = pcm_samples
+            .iter()
+            .flat_map(|sample| sample.to_le_bytes())
+            .collect();
+
+        let pcm_format = PcmFormat {
+            sample_rate: 44_100,
+            channels: 2,
+            bits_per_sample: 16,
+        };
+
+        let mut source_stream = encode_flac_stream(
+            Cursor::new(pcm_bytes.clone()),
+            pcm_format,
+            EncoderOptions::default(),
+        )
+        .await?;
+
+        let mut flac_data = Vec::new();
+        source_stream.read_to_end(&mut flac_data).await?;
+        source_stream.wait().await?;
+
+        let result =
+            transcode_to_flac_stream(Cursor::new(flac_data.clone()), TranscodeOptions::default())
+                .await?;
+
+        assert_eq!(result.input_codec(), AudioCodec::Flac);
+        assert!(result.is_passthrough());
+        assert_eq!(result.input_stream_info().sample_rate, 44_100);
+        assert_eq!(result.input_stream_info().channels, 2);
+
+        let mut stream = result.into_stream();
+        let mut output = Vec::new();
+        stream.read_to_end(&mut output).await?;
+        stream.wait().await?;
+
+        assert_eq!(output, flac_data);
+        Ok(())
+    }
+}