diff --git a/crates/audio/README.md b/crates/audio/README.md
index e05ae3e7c..3f321821d 100644
--- a/crates/audio/README.md
+++ b/crates/audio/README.md
@@ -31,7 +31,7 @@ No default features. The shared types (`AudioBuffer`, `AudioInfo`, `ChannelLayou
 | `encode` | every encoder: the WAV, AIFF and FLAC file writers, and the AAC, ALAC and AC-3/E-AC-3 packet encoders | `lossless-encode`, `aac-encode`, `alac-encode`, `ac3-encode`, `eac3-encode` |
 | `lossless-encode` | WAV, AIFF and FLAC writing | `pcm-encode`, `flac-encode` |
 | `pcm-encode` | `encode`, `FileEncoder` for WAV and AIFF; `wav_float_header` | none |
-| `flac-encode` | `encode`, `FileEncoder` for FLAC | craft-media `bitstream` |
+| `flac-encode` | `encode`, `FileEncoder` for FLAC; `flac::Encoder`, the packet encoder for callers that mux FLAC themselves | craft-media `bitstream` |
 | `aac-decode`, `aac-encode` | `aac::Decoder`, `aac::Encoder` | craft-media `bitstream` |
 | `alac-decode` | `alac::Decoder` | none |
 | `alac-encode` | `alac::Encoder` | none |
diff --git a/crates/audio/src/lib.rs b/crates/audio/src/lib.rs
index 4285ca105..cac8f0291 100644
--- a/crates/audio/src/lib.rs
+++ b/crates/audio/src/lib.rs
@@ -22,7 +22,7 @@
 //! - [`peaks`] (feature `peaks`): min/max/RMS pyramid for waveform drawing.
 //! - Codec modules for packet-level use, each with its own features: [`aac`] (`aac-decode`,
 //!   `aac-encode`), [`alac`] (`alac-decode`, `alac-encode`), [`opus`] (`opus-decode`), [`ac3`]
-//!   (`ac3-decode`), [`mpa`] (`mpa-decode`).
+//!   (`ac3-decode`), [`mpa`] (`mpa-decode`), [`flac`] (`flac-encode`: the packet encoder).
 //!
 //! The shared types below build with no features.
 
@@ -51,6 +51,30 @@ mod wav;
 #[cfg(any(feature = "pcm-encode", feature = "flac-encode"))]
 mod write;
 
+/// The FLAC packet encoder (RFC 9639), for a caller that muxes FLAC itself (into MP4, Matroska or
+/// its own `.flac` writer): planar integer samples in, frames out, and the STREAMINFO to patch in
+/// at the end. [`FileEncoder`] and [`encode`] write whole `.flac` files from `f32` instead.
+///
+/// ```
+/// use craft_audio::flac::{Encoder, EncoderConfig, STREAMINFO_OFFSET};
+///
+/// let left: Vec<i32> = (0..48_000).map(|i| ((i as f64 * 0.05).sin() * 20_000.0) as i32).collect();
+/// let right = left.clone();
+/// let mut enc = Encoder::new(EncoderConfig::new(48_000, 2, 16))?;
+/// let mut file = enc.header(&[]);
+/// file.extend(enc.encode(&[&left, &right])?);
+/// file.extend(enc.finish());
+/// let at = STREAMINFO_OFFSET as usize;
+/// file[at..at + 34].copy_from_slice(&enc.streaminfo());
+/// assert_eq!(&file[..4], b"fLaC");
+/// assert!(file.len() < 48_000 * 2 * 2 / 2); // well under half of 16-bit PCM
+/// # Ok::<(), craft_audio::flac::Error>(())
+/// ```
+#[cfg(feature = "flac-encode")]
+pub mod flac {
+    pub use crate::write::flac::encoder::{Encoder, EncoderConfig, Error, STREAMINFO_OFFSET};
+}
+
 pub use buffer::AudioBuffer;
 /// The craft-media this crate is built with, for its containers: using it rather than a separate
 /// dependency keeps the types the two crates share identical.
@@ -135,6 +159,13 @@ impl From<ac3::encoder::Error> for AudioError {
     }
 }
 
+#[cfg(feature = "flac-encode")]
+impl From<flac::Error> for AudioError {
+    fn from(e: flac::Error) -> Self {
+        AudioError::Encode(format!("FLAC: {e}"))
+    }
+}
+
 #[cfg(feature = "mpa-decode")]
 impl From<mpa::Error> for AudioError {
     fn from(e: mpa::Error) -> Self {
diff --git a/crates/audio/src/write/flac/encoder.rs b/crates/audio/src/write/flac/encoder.rs
index 02a22a0c0..a7a453d20 100644
--- a/crates/audio/src/write/flac/encoder.rs
+++ b/crates/audio/src/write/flac/encoder.rs
@@ -13,18 +13,30 @@ use super::predict::{Effort, Subframe};
 /// Byte offset of the 34-byte STREAMINFO body in [`Encoder::header`].
 pub const STREAMINFO_OFFSET: u64 = 8;
 
+/// Why the encoder refused a configuration or a block of samples.
+#[non_exhaustive]
 #[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
 pub enum Error {
+    /// The configuration is outside what FLAC can code; the text names the field.
     #[error("invalid configuration: {0}")]
     InvalidConfig(&'static str),
+    /// A block had a different number of channels than the configuration.
     #[error("expected {expected} channels, got {got}")]
-    Channels { expected: usize, got: usize },
+    Channels {
+        /// The configured channel count.
+        expected: usize,
+        /// The channels in the block.
+        got: usize,
+    },
+    /// The channels of a block differ in length.
     #[error("channels of unequal length")]
     UnequalChannels,
+    /// A sample is outside the configured sample size.
     #[error("sample {0} does not fit the configured sample size")]
     SampleRange(i32),
 }
 
+/// What to encode and how hard to try.
 #[derive(Clone, Debug)]
 pub struct EncoderConfig {
     /// 1 to 1 048 575 Hz.
@@ -41,11 +53,14 @@ pub struct EncoderConfig {
 }
 
 impl EncoderConfig {
+    /// 4096-sample blocks at level 5.
     pub fn new(sample_rate: u32, channels: u8, bits_per_sample: u8) -> Self {
         EncoderConfig { sample_rate, channels, bits_per_sample, block_size: 4096, level: 5 }
     }
 }
 
+/// The packet encoder: [`Encoder::header`], then frames from [`Encoder::encode`] and
+/// [`Encoder::finish`], then [`Encoder::streaminfo`] over [`STREAMINFO_OFFSET`].
 pub struct Encoder {
     cfg: EncoderConfig,
     effort: Effort,
@@ -61,6 +76,7 @@ pub struct Encoder {
 }
 
 impl Encoder {
+    /// An encoder for `cfg`, or [`Error::InvalidConfig`] when FLAC cannot code it.
     pub fn new(cfg: EncoderConfig) -> Result<Self, Error> {
         if !(1..=8).contains(&cfg.channels) {
             return Err(Error::InvalidConfig("1 to 8 channels"));
@@ -174,6 +190,12 @@ impl Encoder {
         Ok(out)
     }
 
+    /// Samples per channel waiting for a full block: the length of the frame [`Encoder::finish`]
+    /// would write.
+    pub fn pending_samples(&self) -> usize {
+        self.pending.first().map_or(0, Vec::len)
+    }
+
     /// Encode what is left as a final, shorter frame.
     pub fn finish(&mut self) -> Vec<u8> {
         if self.pending.first().is_none_or(Vec::is_empty) {
diff --git a/crates/audio/src/write/flac/mod.rs b/crates/audio/src/write/flac/mod.rs
index f2674d427..6f562e6e2 100644
--- a/crates/audio/src/write/flac/mod.rs
+++ b/crates/audio/src/write/flac/mod.rs
@@ -2,7 +2,7 @@
 //! (linear prediction, stereo decorrelation, STREAMINFO MD5) into any `Write + Seek`.
 
 mod crc;
-mod encoder;
+pub(crate) mod encoder;
 mod frame;
 mod md5;
 mod predict;
@@ -49,7 +49,7 @@ fn mask_comment(channels: usize, mask: Option<u32>) -> Option<String> {
 }
 
 fn encoder_error(e: encoder::Error) -> AudioError {
-    AudioError::Encode(format!("FLAC: {e}"))
+    e.into()
 }
 
 /// A FLAC stream written block by block; [`Writer::finish`] fills in the STREAMINFO sizes, sample
diff --git a/crates/audio/src/write/mod.rs b/crates/audio/src/write/mod.rs
index eaad8e961..25c9b2528 100644
--- a/crates/audio/src/write/mod.rs
+++ b/crates/audio/src/write/mod.rs
@@ -4,7 +4,7 @@
 #[cfg(feature = "pcm-encode")]
 mod aiff;
 #[cfg(feature = "flac-encode")]
-mod flac;
+pub(crate) mod flac;
 mod pcm;
 #[cfg(feature = "pcm-encode")]
 mod wav;