MP4: Support property reading for files with FLAC audio

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Added
 - **Vorbis Comments**: `VorbisComments::{pictures, set_picture, remove_picture}`
 - **Tag**: `Tag::{set_picture, remove_picture}`
+- **MP4**: Support property reading for files with FLAC audio
 
 ### Changed
 - **ID3v2**: `ID3v2Tag` now derives `Eq`

src/flac/block.rs

@@ -5,11 +5,11 @@ use std::io::{Read, Seek};
 
 use byteorder::{BigEndian, ReadBytesExt};
 
-pub(super) struct Block {
+pub(crate) struct Block {
 	pub(super) byte: u8,
 	pub(super) ty: u8,
 	pub(super) last: bool,
-	pub(super) content: Vec<u8>,
+	pub(crate) content: Vec<u8>,
 	pub(super) start: u64,
 	pub(super) end: u64,
 }

src/flac/mod.rs

@@ -4,8 +4,8 @@
 //!
 //! * See [`FlacFile`]
 
-mod block;
-mod properties;
+pub(crate) mod block;
+pub(crate) mod properties;
 mod read;
 #[cfg(feature = "vorbis_comments")]
 pub(crate) mod write;

src/flac/properties.rs

@@ -47,8 +47,9 @@ where
 
 	if sample_rate > 0 && total_samples > 0 {
 		let length = (u64::from(total_samples) * 1000) / u64::from(sample_rate);
-		if length > 0 {
-			properties.duration = Duration::from_millis(length);
+		properties.duration = Duration::from_millis(length);
+
+		if length > 0 && file_length > 0 && stream_length > 0 {
 			properties.overall_bitrate = Some(((file_length * 8) / length) as u32);
 			properties.audio_bitrate = Some(((stream_length * 8) / length) as u32);
 		}

src/mp4/properties.rs

@@ -20,6 +20,7 @@ pub enum Mp4Codec {
 	AAC,
 	ALAC,
 	MP3,
+	FLAC,
 }
 
 impl Default for Mp4Codec {
@@ -341,9 +342,9 @@ where
 					match fourcc {
 						b"mp4a" => mp4a_properties(&mut stsd_reader, &mut properties)?,
 						b"alac" => alac_properties(&mut stsd_reader, &mut properties)?,
+						b"fLaC" => flac_properties(&mut stsd_reader, &mut properties)?,
 						// Maybe do these?
-						// TODO: dfla (https://github.com/xiph/flac/blob/master/doc/isoflac.txt)
-						// TODO: dops
+						// TODO: dops (opus)
 						// TODO: wave (https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html#//apple_ref/doc/uid/TP40000939-CH205-134202)
 						_ => {},
 					}
@@ -585,6 +586,64 @@ where
 	Ok(())
 }
 
+fn flac_properties<R>(stsd: &mut R, properties: &mut Mp4Properties) -> Result<()>
+where
+	R: Read + Seek,
+{
+	properties.codec = Mp4Codec::FLAC;
+
+	// Skipping 16 bytes
+	//
+	// Reserved (6)
+	// Data reference index (2)
+	// Version (2)
+	// Revision level (2)
+	// Vendor (4)
+	stsd.seek(SeekFrom::Current(16))?;
+
+	properties.channels = stsd.read_u16::<BigEndian>()? as u8;
+	properties.bit_depth = Some(stsd.read_u16::<BigEndian>()? as u8);
+
+	// Skipping 4 bytes
+	//
+	// Compression ID (2)
+	// Packet size (2)
+	stsd.seek(SeekFrom::Current(4))?;
+
+	properties.sample_rate = u32::from(stsd.read_u16::<BigEndian>()?);
+
+	let _reserved = stsd.read_u16::<BigEndian>()?;
+
+	let dfla_atom = AtomInfo::read(stsd)?;
+	match dfla_atom.ident {
+		// There should be a dfla atom, but it's not worth erroring if absent.
+		AtomIdent::Fourcc(ref fourcc) if fourcc == b"dfla" => {},
+		_ => return Ok(()),
+	}
+
+	// Skipping 4 bytes
+	//
+	// Version (1)
+	// Flags (3)
+	stsd.seek(SeekFrom::Current(4))?;
+
+	if dfla_atom.len - 12 < 18 {
+		// The atom isn't long enough to hold a STREAMINFO block, also not worth an error.
+		return Ok(());
+	}
+
+	let stream_info_block = crate::flac::block::Block::read(stsd)?;
+	let flac_properties =
+		crate::flac::properties::read_properties(&mut &stream_info_block.content[..], 0, 0)?;
+
+	// Safe to unwrap, since these fields are guaranteed to be present
+	properties.sample_rate = flac_properties.sample_rate.unwrap();
+	properties.bit_depth = flac_properties.bit_depth;
+	properties.channels = flac_properties.channels.unwrap();
+
+	Ok(())
+}
+
 // Used to calculate the bitrate, when it isn't readily available to us
 fn mdat_length<R>(data: &mut R) -> Result<u64>
 where

src/properties.rs

@@ -153,6 +153,17 @@ mod tests {
 		channels: 2,
 	};
 
+	const MP4_FLAC_PROPERTIES: Mp4Properties = Mp4Properties {
+		codec: Mp4Codec::FLAC,
+		extended_audio_object_type: None,
+		duration: Duration::from_millis(1428),
+		overall_bitrate: 280, // TODO: FFmpeg reports 279
+		audio_bitrate: 275,
+		sample_rate: 48000,
+		bit_depth: Some(16),
+		channels: 2,
+	};
+
 	const OPUS_PROPERTIES: OpusProperties = OpusProperties {
 		duration: Duration::from_millis(1428),
 		overall_bitrate: 120,
@@ -275,6 +286,14 @@ mod tests {
 		)
 	}
 
+	#[test]
+	fn mp4_flac_properties() {
+		assert_eq!(
+			get_properties::<Mp4File>("tests/files/assets/minimal/mp4_codec_flac.mp4"),
+			MP4_FLAC_PROPERTIES
+		)
+	}
+
 	#[test]
 	fn opus_properties() {
 		assert_eq!(