clack_host/process/

audio_buffers.rs

//! Types to manipulate input and output audio buffers for processing.

use crate::util::check_collection_clap_size_overflow;
use clack_common::process::AudioPortProcessingInfo;
use clap_sys::audio_buffer::clap_audio_buffer;
use core::array::IntoIter;

pub struct InputChannel<'a, T> {
    pub buffer: &'a mut [T],
    pub is_constant: bool,
}

impl<'a, T> InputChannel<'a, T> {
    #[inline]
    pub fn from_buffer<D: ?Sized + AsMut<[T]> + 'a>(buffer: &'a mut D, is_constant: bool) -> Self {
        Self {
            buffer: buffer.as_mut(),
            is_constant,
        }
    }

    #[inline]
    pub fn variable<D: ?Sized + AsMut<[T]> + 'a>(buffer: &'a mut D) -> Self {
        Self::from_buffer(buffer, false)
    }

    #[inline]
    pub fn constant<D: ?Sized + AsMut<[T]> + 'a>(buffer: &'a mut D) -> Self {
        Self::from_buffer(buffer, true)
    }
}

pub enum AudioPortBufferType<I32, I64> {
    F32(I32),
    F64(I64),
}

impl<I32> AudioPortBufferType<I32, IntoIter<InputChannel<'static, f64>, 0>> {
    #[inline]
    pub fn f32_input_only(iterator: I32) -> Self {
        Self::F32(iterator)
    }
}

impl<I32> AudioPortBufferType<I32, IntoIter<&'static mut [f64], 0>> {
    #[inline]
    pub fn f32_output_only(iterator: I32) -> Self {
        Self::F32(iterator)
    }
}

impl<I64> AudioPortBufferType<IntoIter<InputChannel<'static, f32>, 0>, I64> {
    #[inline]
    pub fn f64_input_only(iterator: I64) -> Self {
        Self::F64(iterator)
    }
}

impl<I64> AudioPortBufferType<IntoIter<&'static mut [f32], 0>, I64> {
    #[inline]
    pub fn f64_output_only(iterator: I64) -> Self {
        Self::F64(iterator)
    }
}

pub struct AudioPortBuffer<I32, I64> {
    pub channels: AudioPortBufferType<I32, I64>,
    pub latency: u32,
}

// bikeshed
pub struct AudioPorts {
    buffer_lists: Vec<*mut f32>, // Can be f32 or f64, cast on-demand
    buffer_configs: Vec<clap_audio_buffer>,
}

// SAFETY: The pointers are only temporary storage, they are not used unless AudioPorts is exclusively borrowed
unsafe impl Send for AudioPorts {}
// SAFETY: The pointers are only temporary storage, they are not used unless AudioPorts is exclusively borrowed
unsafe impl Sync for AudioPorts {}

impl AudioPorts {
    #[cfg(feature = "clack-plugin")]
    pub fn from_plugin_audio_mut<'a>(
        audio: &'a mut clack_plugin::prelude::Audio,
    ) -> (InputAudioBuffers<'a>, OutputAudioBuffers<'a>) {
        let frames_count = audio.frames_count();
        let (ins, outs) = audio.raw_buffers();

        // SAFETY: the validity of the buffers is guaranteed by the Audio type
        unsafe {
            (
                InputAudioBuffers::from_raw_buffers(ins, frames_count),
                OutputAudioBuffers::from_raw_buffers(outs, frames_count),
            )
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn from_plugin_audio(
        audio: clack_plugin::prelude::Audio,
    ) -> (InputAudioBuffers, OutputAudioBuffers) {
        let frames_count = audio.frames_count();
        let (ins, outs) = audio.to_raw_buffers();

        // SAFETY: the validity of the buffers is guaranteed by the Audio type
        unsafe {
            (
                InputAudioBuffers::from_raw_buffers(ins, frames_count),
                OutputAudioBuffers::from_raw_buffers(outs, frames_count),
            )
        }
    }

    pub fn with_capacity(total_channel_count: usize, port_count: usize) -> Self {
        let mut bufs = Self {
            buffer_configs: Vec::with_capacity(port_count),
            buffer_lists: Vec::with_capacity(total_channel_count),
        };
        bufs.resize_buffer_configs(port_count);

        bufs
    }

    #[inline]
    pub fn port_capacity(&self) -> usize {
        self.buffer_configs.len()
    }

    fn resize_buffer_configs(&mut self, new_size: usize) {
        if new_size > self.buffer_configs.len() {
            self.buffer_configs.resize(
                new_size,
                clap_audio_buffer {
                    data32: core::ptr::null_mut(),
                    data64: core::ptr::null_mut(),
                    channel_count: 0,
                    latency: 0,
                    constant_mask: 0,
                },
            );
        }
    }

    pub fn with_input_buffers<'a, I, Iter, ChannelIter32, ChannelIter64>(
        &'a mut self,
        iter: I,
    ) -> InputAudioBuffers<'a>
    where
        I: IntoIterator<Item = AudioPortBuffer<ChannelIter32, ChannelIter64>, IntoIter = Iter>,
        Iter: ExactSizeIterator<Item = AudioPortBuffer<ChannelIter32, ChannelIter64>>,
        ChannelIter32: IntoIterator<Item = InputChannel<'a, f32>>,
        ChannelIter64: IntoIterator<Item = InputChannel<'a, f64>>,
    {
        let iter = iter.into_iter();
        self.resize_buffer_configs(iter.len());
        self.buffer_lists.clear();

        let mut min_channel_buffer_length = u32::MAX;
        let mut total = 0;
        let mut has_reallocated = false;

        for (i, port) in iter.enumerate() {
            total = i + 1;

            let last = self.buffer_lists.len();

            let mut constant_mask = 0u64;
            let is_f64 = match port.channels {
                AudioPortBufferType::F32(channels) => {
                    for channel in channels {
                        min_channel_buffer_length = min_channel_buffer_length
                            .min(saturate_usize_to_clap_size(channel.buffer.len()));
                        if channel.is_constant {
                            constant_mask |= 1 << i as u64
                        }

                        check_collection_clap_size_overflow(&self.buffer_lists);

                        if self.buffer_lists.len() >= self.buffer_lists.capacity() {
                            has_reallocated = true;
                        }

                        self.buffer_lists.push(channel.buffer.as_mut_ptr().cast())
                    }
                    false
                }
                AudioPortBufferType::F64(channels) => {
                    for channel in channels {
                        min_channel_buffer_length = min_channel_buffer_length
                            .min(saturate_usize_to_clap_size(channel.buffer.len()));
                        if channel.is_constant {
                            constant_mask |= 1 << i as u64
                        }

                        check_collection_clap_size_overflow(&self.buffer_lists);

                        if self.buffer_lists.len() >= self.buffer_lists.capacity() {
                            has_reallocated = true;
                        }

                        self.buffer_lists.push(channel.buffer.as_mut_ptr().cast())
                    }
                    true
                }
            };

            let buffers = self.buffer_lists.get_mut(last..).unwrap_or(&mut []);

            // PANIC: this can only panic with an invalid implementation of ExactSizeIterator
            let descriptor = &mut self.buffer_configs[i];
            #[allow(clippy::cast_possible_truncation)]
            // We already checked above that it cannot be overflowed
            {
                descriptor.channel_count = buffers.len() as u32;
            }
            descriptor.latency = port.latency;
            descriptor.constant_mask = constant_mask;

            if is_f64 {
                descriptor.data64 = buffers.as_mut_ptr().cast();
                descriptor.data32 = core::ptr::null_mut();
            } else {
                descriptor.data64 = core::ptr::null_mut();
                descriptor.data32 = buffers.as_mut_ptr();
            }
        }

        // If a realloc occurred, we must rewrite all the pointers.
        // Thankfully, we know we wrote them sequentially, and we stored the lengths, so it's easy
        // to find them back.
        if has_reallocated {
            let mut last_len = 0;
            for descriptor in &mut self.buffer_configs[..total] {
                let channel_count = descriptor.channel_count as usize;
                let buffers = self
                    .buffer_lists
                    .get_mut(last_len..channel_count)
                    .unwrap_or(&mut []);
                last_len += channel_count;

                if descriptor.data32.is_null() {
                    descriptor.data64 = buffers.as_mut_ptr().cast();
                } else {
                    descriptor.data32 = buffers.as_mut_ptr();
                }
            }
        }

        InputAudioBuffers {
            buffers: &self.buffer_configs[..total],
            frames_count: if min_channel_buffer_length == u32::MAX {
                None
            } else {
                Some(min_channel_buffer_length)
            },
        }
    }

    pub fn with_output_buffers<'a, I, Iter, ChannelIter32, ChannelIter64>(
        &'a mut self,
        iter: I,
    ) -> OutputAudioBuffers<'a>
    where
        I: IntoIterator<Item = AudioPortBuffer<ChannelIter32, ChannelIter64>, IntoIter = Iter>,
        Iter: ExactSizeIterator<Item = AudioPortBuffer<ChannelIter32, ChannelIter64>>,
        ChannelIter32: IntoIterator<Item = &'a mut [f32]>,
        ChannelIter64: IntoIterator<Item = &'a mut [f64]>,
    {
        let iter = iter.into_iter();
        self.resize_buffer_configs(iter.len());
        self.buffer_lists.clear();

        let mut min_channel_buffer_length = u32::MAX;
        let mut total = 0;
        let mut has_reallocated = false;

        for (i, port) in iter.enumerate() {
            total = i + 1;

            let last = self.buffer_lists.len();

            let is_f64 = match port.channels {
                AudioPortBufferType::F32(channels) => {
                    for channel in channels {
                        min_channel_buffer_length = min_channel_buffer_length
                            .min(saturate_usize_to_clap_size(channel.len()));

                        check_collection_clap_size_overflow(&self.buffer_lists);

                        if self.buffer_lists.len() >= self.buffer_lists.capacity() {
                            has_reallocated = true;
                        }

                        self.buffer_lists.push(channel.as_mut_ptr().cast())
                    }
                    false
                }
                AudioPortBufferType::F64(channels) => {
                    for channel in channels {
                        min_channel_buffer_length = min_channel_buffer_length
                            .min(saturate_usize_to_clap_size(channel.len()));

                        check_collection_clap_size_overflow(&self.buffer_lists);

                        if self.buffer_lists.len() >= self.buffer_lists.capacity() {
                            has_reallocated = true;
                        }

                        self.buffer_lists.push(channel.as_mut_ptr().cast())
                    }
                    true
                }
            };

            let buffers = self.buffer_lists.get_mut(last..).unwrap_or(&mut []);

            // PANIC: this can only panic with an invalid implementation of ExactSizeIterator
            let descriptor = &mut self.buffer_configs[i];
            #[allow(clippy::cast_possible_truncation)]
            // We already checked above that it cannot be overflowed
            {
                descriptor.channel_count = buffers.len() as u32;
            }
            descriptor.latency = port.latency;
            descriptor.constant_mask = 0;

            if is_f64 {
                descriptor.data64 = buffers.as_mut_ptr().cast();
                descriptor.data32 = core::ptr::null_mut();
            } else {
                descriptor.data64 = core::ptr::null_mut();
                descriptor.data32 = buffers.as_mut_ptr();
            }
        }

        // If a realloc occurred, we must rewrite all the pointers.
        // Thankfully, we know we wrote them sequentially, and we stored the lengths, so it's easy
        // to find them back.
        if has_reallocated {
            let mut last_len = 0;
            for descriptor in &mut self.buffer_configs[..total] {
                let channel_count = descriptor.channel_count as usize;
                let buffers = self
                    .buffer_lists
                    .get_mut(last_len..channel_count)
                    .unwrap_or(&mut []);
                last_len += channel_count;

                if descriptor.data32.is_null() {
                    descriptor.data64 = buffers.as_mut_ptr().cast();
                } else {
                    descriptor.data32 = buffers.as_mut_ptr();
                }
            }
        }

        OutputAudioBuffers {
            buffers: &mut self.buffer_configs[..total],
            frames_count: if min_channel_buffer_length == u32::MAX {
                None
            } else {
                Some(min_channel_buffer_length)
            },
        }
    }

    #[inline]
    pub fn port_count(&self) -> usize {
        self.buffer_configs.len()
    }
}

#[inline]
const fn saturate_usize_to_clap_size(value: usize) -> u32 {
    if value > u32::MAX as usize {
        u32::MAX - 1
    } else {
        #[allow(clippy::cast_possible_truncation)] // We just checked it above, it cannot overflow
        {
            value as u32
        }
    }
}

pub struct InputAudioBuffers<'a> {
    buffers: &'a [clap_audio_buffer],
    frames_count: Option<u32>,
}

impl<'a> InputAudioBuffers<'a> {
    #[inline]
    pub const fn empty() -> Self {
        Self {
            buffers: &[],
            frames_count: None,
        }
    }

    /// Shortens the [`frames_count`] of these input buffers.
    ///
    /// This does not actually change the underlying buffers themselves, it only reduces the
    /// slice that will be exposed to the plugin.
    ///
    /// This method does nothing if `max_buffer_size` is greater or equal than the current [`frames_count`].
    ///
    /// [`frames_count`]: self.frames_count
    pub fn truncate(&mut self, max_buffer_size: u32) {
        if let Some(frames_count) = self.frames_count {
            self.frames_count = Some(frames_count.min(max_buffer_size))
        }
    }

    /// # Safety
    ///
    /// The caller must ensure all buffer structs are valid for 'a, including all the buffer
    /// pointers they contain.
    ///
    /// The caller must also ensure `frames_count` is lower than or equal to the sizes of the
    /// channel buffers pointed to by `buffers`.
    #[inline]
    pub unsafe fn from_raw_buffers(buffers: &'a [clap_audio_buffer], frames_count: u32) -> Self {
        check_collection_clap_size_overflow(buffers);

        Self {
            buffers,
            frames_count: Some(frames_count),
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn from_plugin_audio(audio: &clack_plugin::prelude::Audio<'a>) -> InputAudioBuffers<'a> {
        let frames_count = audio.frames_count();
        let ins = audio.raw_input_buffers();

        // SAFETY: the validity of the buffers is guaranteed by the Audio type
        unsafe { InputAudioBuffers::from_raw_buffers(ins, frames_count) }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn as_plugin_audio(&self) -> clack_plugin::prelude::Audio<'a> {
        // SAFETY: the validity of the buffers is guaranteed by this type
        unsafe {
            clack_plugin::prelude::Audio::from_raw_buffers(
                self.buffers,
                &mut [],
                self.frames_count.unwrap_or(0),
            )
        }
    }

    #[inline]
    pub fn as_raw_buffers(&self) -> &'a [clap_audio_buffer] {
        self.buffers
    }

    /// The number of port buffers this [`InputAudioBuffers`] has been given.
    #[inline]
    pub fn port_count(&self) -> u32 {
        #[allow(clippy::cast_possible_truncation)]
        // We checked above that buffers' len cannot overflow u32
        {
            self.buffers.len() as u32
        }
    }

    /// The number of frames in these input buffers.
    ///
    /// This is the minimum frame count of all the port buffers this has been given.
    ///
    /// If this has no port buffer (i.e. [`port_count`](self.port_count) is zero), this returns `None`.
    #[inline]
    pub fn frames_count(&self) -> Option<u32> {
        self.frames_count
    }

    #[inline]
    pub fn port_info(&self, port_index: u32) -> Option<AudioPortProcessingInfo> {
        self.buffers
            .get(port_index as usize)
            .map(AudioPortProcessingInfo::from_raw)
    }

    #[inline]
    pub fn port_infos(&self) -> impl Iterator<Item = AudioPortProcessingInfo> + '_ {
        self.buffers.iter().map(AudioPortProcessingInfo::from_raw)
    }

    /// Returns the minimum number of frames available both in this [`InputAudioBuffers`] and
    /// the given [`OutputAudioBuffers`].
    ///
    /// This is useful to ensure a safe frame count for a `process` batch that would receive those
    /// input and output audio buffers.
    pub fn min_available_frames_with(&self, outputs: &OutputAudioBuffers) -> u32 {
        match (self.frames_count, outputs.frames_count) {
            (Some(a), Some(b)) => a.min(b),
            (Some(a), None) | (None, Some(a)) => a,
            (None, None) => 0,
        }
    }
}

pub struct OutputAudioBuffers<'a> {
    buffers: &'a mut [clap_audio_buffer],
    frames_count: Option<u32>,
}

impl<'a> OutputAudioBuffers<'a> {
    #[inline]
    pub fn empty() -> Self {
        Self {
            buffers: &mut [],
            frames_count: None,
        }
    }

    /// Shortens the [`frames_count`] of these output buffers.
    ///
    /// This does not actually change the underlying buffers themselves, it only reduces the
    /// slice that will be exposed to the plugin.
    ///
    /// This method does nothing if `max_buffer_size` is greater or equal than the current [`frames_count`].
    ///
    /// [`frames_count`]: self.frames_count
    pub fn truncate(&mut self, max_buffer_size: u32) {
        if let Some(frames_count) = self.frames_count {
            self.frames_count = Some(frames_count.min(max_buffer_size))
        }
    }

    /// # Safety
    ///
    /// The caller must ensure all buffer structs are valid for 'a, including all the buffer
    /// pointers they contain.
    ///
    /// The caller must also ensure `frames_count` is lower than or equal to the sizes of the
    /// channel buffers pointed to by `buffers`.
    #[inline]
    pub unsafe fn from_raw_buffers(
        buffers: &'a mut [clap_audio_buffer],
        frames_count: u32,
    ) -> Self {
        check_collection_clap_size_overflow(buffers);

        Self {
            buffers,
            frames_count: Some(frames_count),
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn from_plugin_audio(audio: clack_plugin::prelude::Audio<'a>) -> OutputAudioBuffers<'a> {
        let frames_count = audio.frames_count();
        let outs = audio.to_raw_output_buffers();

        // SAFETY: the validity of the buffers is guaranteed by the Audio type
        unsafe { OutputAudioBuffers::from_raw_buffers(outs, frames_count) }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn from_plugin_audio_mut(
        audio: &'a mut clack_plugin::prelude::Audio,
    ) -> OutputAudioBuffers<'a> {
        let frames_count = audio.frames_count();
        let outs = audio.raw_output_buffers();

        // SAFETY: the validity of the buffers is guaranteed by the Audio type
        unsafe { OutputAudioBuffers::from_raw_buffers(outs, frames_count) }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn as_plugin_audio(&'a mut self) -> clack_plugin::prelude::Audio<'a> {
        // SAFETY: the validity of the buffers is guaranteed by this type
        unsafe {
            clack_plugin::prelude::Audio::from_raw_buffers(
                &[],
                self.buffers,
                self.frames_count.unwrap_or(0),
            )
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn to_plugin_audio(self) -> clack_plugin::prelude::Audio<'a> {
        // SAFETY: the validity of the buffers is guaranteed by this type
        unsafe {
            clack_plugin::prelude::Audio::from_raw_buffers(
                &[],
                self.buffers,
                self.frames_count.unwrap_or(0),
            )
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn as_plugin_audio_with_inputs(
        &'a mut self,
        inputs: &InputAudioBuffers<'a>,
    ) -> clack_plugin::prelude::Audio<'a> {
        let frames_count = inputs.min_available_frames_with(self);

        // SAFETY: the validity of the buffers is guaranteed by this type
        unsafe {
            clack_plugin::prelude::Audio::from_raw_buffers(
                inputs.buffers,
                self.buffers,
                frames_count,
            )
        }
    }

    #[cfg(feature = "clack-plugin")]
    pub fn to_plugin_audio_with_inputs(
        self,
        inputs: &InputAudioBuffers<'a>,
    ) -> clack_plugin::prelude::Audio<'a> {
        let frames_count = inputs.min_available_frames_with(&self);

        // SAFETY: the validity of the buffers is guaranteed by this type
        unsafe {
            clack_plugin::prelude::Audio::from_raw_buffers(
                inputs.buffers,
                self.buffers,
                frames_count,
            )
        }
    }

    #[inline]
    pub fn as_raw_buffers(&mut self) -> &mut [clap_audio_buffer] {
        self.buffers
    }

    #[inline]
    pub fn into_raw_buffers(self) -> &'a mut [clap_audio_buffer] {
        self.buffers
    }

    /// The number of port buffers this [`OutputAudioBuffers`] has been given.
    #[inline]
    pub fn port_count(&self) -> u32 {
        #[allow(clippy::cast_possible_truncation)]
        // We checked above that buffers' len cannot overflow u32
        {
            self.buffers.len() as u32
        }
    }

    /// The number of frames in these output buffers.
    ///
    /// This is the minimum frame count of all the port buffers this has been given.
    ///
    /// If this has no port buffer (i.e. [`port_count`](self.port_count) is zero), this returns `None`.
    #[inline]
    pub fn frames_count(&self) -> Option<u32> {
        self.frames_count
    }

    #[inline]
    pub fn port_info(&self, port_index: u32) -> Option<AudioPortProcessingInfo> {
        self.buffers
            .get(port_index as usize)
            .map(AudioPortProcessingInfo::from_raw)
    }

    #[inline]
    pub fn port_infos(&self) -> impl Iterator<Item = AudioPortProcessingInfo> + '_ {
        self.buffers.iter().map(AudioPortProcessingInfo::from_raw)
    }
}

#[cfg(test)]
mod test {
    use super::*;
    use clack_plugin::prelude::*;
    use clap_sys::process::clap_process;
    use std::cell::RefCell;
    use std::ptr::null_mut;

    #[test]
    pub fn input_audio_buffers_work() {
        let mut ports = AudioPorts::with_capacity(2, 1);
        let mut bufs = [[0f32; 4]; 2];

        let buffers = ports.with_input_buffers([AudioPortBuffer {
            latency: 0,
            channels: AudioPortBufferType::f32_input_only(bufs.iter_mut().map(|b| InputChannel {
                buffer: b.as_mut_slice(),
                is_constant: false,
            })),
        }]);

        assert_eq!(buffers.buffers.len(), 1);
        assert_eq!(buffers.frames_count, Some(4));
    }

    #[test]
    pub fn output_audio_buffers_work() {
        let mut ports = AudioPorts::with_capacity(2, 1);
        let mut bufs = [[0f32; 4]; 2];

        let buffers = ports.with_output_buffers([AudioPortBuffer {
            latency: 0,
            channels: AudioPortBufferType::f32_output_only(
                bufs.iter_mut().map(|b| b.as_mut_slice()),
            ),
        }]);

        assert_eq!(buffers.buffers.len(), 1);
        assert_eq!(buffers.frames_count, Some(4));

        assert_eq!(bufs.len(), 2); // Check borrow still works
        assert_eq!(ports.port_count(), 1);
    }

    #[test]
    pub fn input_audio_buffers_work_with_refcell() {
        let mut ports = AudioPorts::with_capacity(2, 1);
        let bufs = [RefCell::new([0f32; 4]), RefCell::new([0f32; 4])];
        let mut borrowed: Vec<_> = bufs.iter().map(|c| c.borrow_mut()).collect();

        let buffers = ports.with_input_buffers([AudioPortBuffer {
            latency: 0,
            channels: AudioPortBufferType::f32_input_only(borrowed.iter_mut().map(|b| {
                InputChannel {
                    buffer: b.as_mut_slice(),
                    is_constant: false,
                }
            })),
        }]);

        assert_eq!(buffers.buffers.len(), 1);
        assert_eq!(buffers.frames_count, Some(4));
    }

    #[test]
    pub fn output_audio_buffers_work_with_refcell() {
        let mut ports = AudioPorts::with_capacity(2, 1);
        let bufs = [RefCell::new([0f32; 4]), RefCell::new([0f32; 4])];
        let mut borrowed: Vec<_> = bufs.iter().map(|c| c.borrow_mut()).collect();

        let buffers = ports.with_output_buffers([AudioPortBuffer {
            latency: 0,
            channels: AudioPortBufferType::f32_output_only(
                borrowed.iter_mut().map(|b| b.as_mut_slice()),
            ),
        }]);

        assert_eq!(buffers.buffers.len(), 1);
        assert_eq!(buffers.frames_count, Some(4));

        assert_eq!(bufs.len(), 2); // Check borrow still works
        assert_eq!(ports.port_count(), 1);
    }

    #[test]
    pub fn audio_buffers_work_with_wrong_capacity() {
        let mut input_ports = AudioPorts::with_capacity(1, 1);
        let mut output_ports = AudioPorts::with_capacity(1, 1);
        let mut input_bufs = [[[42f32; 4]; 128], [[69f32; 4]; 128]];
        let mut output_bufs = [[[42f32; 4]; 128], [[69f32; 4]; 128]];

        let input_buffers =
            input_ports.with_input_buffers(input_bufs.iter_mut().map(|bufs| AudioPortBuffer {
                latency: 0,
                channels: AudioPortBufferType::f32_input_only(bufs.iter_mut().map(|b| {
                    InputChannel {
                        buffer: b.as_mut_slice(),
                        is_constant: false,
                    }
                })),
            }));

        let mut output_buffers =
            output_ports.with_output_buffers(output_bufs.iter_mut().map(|bufs| AudioPortBuffer {
                latency: 0,
                channels: AudioPortBufferType::f32_output_only(
                    bufs.iter_mut().map(|b| b.as_mut_slice()),
                ),
            }));

        assert_eq!(input_buffers.buffers.len(), 2);
        assert_eq!(input_buffers.frames_count, Some(4));
        assert_eq!(output_buffers.buffers.len(), 2);
        assert_eq!(output_buffers.frames_count, Some(4));

        let raw_input_buffers = input_buffers.as_raw_buffers();
        let raw_output_buffers = output_buffers.as_raw_buffers();
        let process = clap_process {
            audio_inputs: raw_input_buffers.as_ptr(),
            audio_outputs: raw_output_buffers.as_ptr() as *mut _,
            audio_inputs_count: input_buffers.port_count(),
            audio_outputs_count: output_buffers.port_count(),

            steady_time: 0,
            frames_count: 4,
            transport: null_mut(),
            in_events: null_mut(),
            out_events: null_mut(),
        };

        // SAFETY: we built the process struct above, it should be good.
        let mut audio = unsafe { Audio::from_raw(&process) };

        for (port, bufs) in audio.input_ports().zip(&input_bufs) {
            let channels = port.channels().unwrap().into_f32().unwrap();

            assert_eq!(channels.channel_count(), 128);
            for (channel, buf) in channels.iter().zip(bufs.iter()) {
                assert_eq!(buf, channel)
            }
        }

        for (mut port, bufs) in audio.output_ports().zip(&output_bufs) {
            let channels = port.channels().unwrap().into_f32().unwrap();

            assert_eq!(channels.channel_count(), 128);
            for (channel, buf) in channels.iter().zip(bufs.iter()) {
                assert_eq!(buf, channel)
            }
        }
    }
}