Opus: Create a ChannelMask for OpusProperties

src/ogg/opus/properties.rs

@@ -2,7 +2,7 @@ use super::find_last_page;
 use crate::error::Result;
 use crate::macros::decode_err;
 use crate::math::RoundedDivision;
-use crate::properties::FileProperties;
+use crate::properties::{ChannelMask, FileProperties};
 
 use std::io::{Read, Seek, SeekFrom};
 use std::time::Duration;
@@ -18,6 +18,7 @@ pub struct OpusProperties {
 	pub(crate) overall_bitrate: u32,
 	pub(crate) audio_bitrate: u32,
 	pub(crate) channels: u8,
+	pub(crate) channel_mask: ChannelMask,
 	pub(crate) version: u8,
 	pub(crate) input_sample_rate: u32,
 }
@@ -31,7 +32,7 @@ impl From<OpusProperties> for FileProperties {
 			sample_rate: Some(input.input_sample_rate),
 			bit_depth: None,
 			channels: Some(input.channels),
-			channel_mask: None,
+			channel_mask: Some(input.channel_mask),
 		}
 	}
 }
@@ -57,6 +58,11 @@ impl OpusProperties {
 		self.channels
 	}
 
+	/// Channel mask
+	pub fn channel_mask(&self) -> ChannelMask {
+		self.channel_mask
+	}
+
 	/// Opus version
 	pub fn version(&self) -> u8 {
 		self.version
@@ -103,6 +109,9 @@ where
 		decode_err!(@BAIL Opus, "Invalid channel count for mapping family");
 	}
 
+	properties.channel_mask =
+		ChannelMask::from_opus_channels(properties.channels).expect("Channel count is valid");
+
 	let last_page = find_last_page(data);
 	let file_length = data.seek(SeekFrom::End(0))?;
 

src/properties/channel_mask.rs

@@ -66,11 +66,59 @@ impl ChannelMask {
 		Self(Self::FRONT_LEFT.0 | Self::FRONT_RIGHT.0)
 	}
 
+	/// Front left+right+center channels
+	#[must_use]
+	pub const fn linear_surround() -> Self {
+		Self(Self::FRONT_LEFT.0 | Self::FRONT_RIGHT.0 | Self::FRONT_CENTER.0)
+	}
+
 	/// The bit mask
 	#[must_use]
 	pub const fn bits(self) -> u32 {
 		self.0
 	}
+
+	/// Create a channel mask from the number of channels in an Opus file
+	///
+	/// See <https://datatracker.ietf.org/doc/html/rfc7845#section-5.1.1.2> for the mapping.
+	pub const fn from_opus_channels(channels: u8) -> Option<Self> {
+		match channels {
+			1 => Some(Self::mono()),
+			2 => Some(Self::stereo()),
+			3 => Some(Self::linear_surround()),
+			4 => Some(Self(
+				Self::FRONT_LEFT.bits()
+					| Self::FRONT_RIGHT.bits()
+					| Self::BACK_LEFT.bits()
+					| Self::BACK_RIGHT.bits(),
+			)),
+			5 => Some(Self(
+				Self::linear_surround().bits() | Self::BACK_LEFT.bits() | Self::BACK_RIGHT.bits(),
+			)),
+			6 => Some(Self(
+				Self::linear_surround().bits()
+					| Self::BACK_LEFT.bits()
+					| Self::BACK_RIGHT.bits()
+					| Self::LOW_FREQUENCY.bits(),
+			)),
+			7 => Some(Self(
+				Self::linear_surround().bits()
+					| Self::SIDE_LEFT.bits()
+					| Self::SIDE_RIGHT.bits()
+					| Self::BACK_CENTER.bits()
+					| Self::LOW_FREQUENCY.bits(),
+			)),
+			8 => {
+				Some(Self(
+					Self::linear_surround().bits()
+						| Self::SIDE_LEFT.bits() | Self::SIDE_RIGHT.bits()
+						| Self::BACK_LEFT.bits() | Self::BACK_RIGHT.bits()
+						| Self::LOW_FREQUENCY.bits(),
+				))
+			},
+			_ => None,
+		}
+	}
 }
 
 impl BitOr for ChannelMask {

src/properties/tests.rs

@@ -229,6 +229,7 @@ const OPUS_PROPERTIES: OpusProperties = OpusProperties {
 	overall_bitrate: 120,
 	audio_bitrate: 120,
 	channels: 2,
+	channel_mask: ChannelMask::stereo(),
 	version: 1,
 	input_sample_rate: 48000,
 };