[Question] turn a Sample to &[u8]?

[Geobert]

Hi,

I'm using master branch on 624ba659da7ed97cd973d98fe1c0eae331a6f84c so I can follow the examples folder :). I'm trying to send a Sample over TCP using tokio and I'm reaching a point where I want to have a &[u8] out of a cpal::Sample.

Is there a simple way to achieve that?

Regards,

[didoloan]

let bytes:&[u8] = unsafe { core::mem::transmute::<&[f32], &[u8]>(sample) };

[Klohger]

let bytes:&[u8] = unsafe { core::mem::transmute::<&[f32], &[u8]>(sample) };

If you have a slice of samples, I would not recommend this, as directly transmuting between slices is UB if I recall, plus the size will most likely be wrong. Do something like this instead:

pub fn slice_to_u8_slice<T>(slice: &[T]) -> &[u8] {
    unsafe { core::slice::from_raw_parts(slice.as_ptr().cast(), core::mem::size_of_val(slice)) }
}
let bytes = slice_to_u8_slice(&[
    0.0f32, 0.5f32, 1.0f32, 0.5f32, 0.0f32, -0.5f32, -1.0f32, -0.5f32,
]);

If you only want to convert one sample then I would probably create a trait akin to this:

pub trait Buf: Sized {
    fn buf(&self) -> &[u8] {
        unsafe {
            core::slice::from_raw_parts(
                core::ptr::from_ref(self).cast(),
                core::mem::size_of::<Self>(),
            )
        }
    }
}
impl Buf for u8 {
    fn buf(&self) -> &[u8] {
        core::slice::from_ref(self)
    }
}
impl Buf for i8 {
    fn buf(&self) -> &[u8] {
        core::slice::from_ref(unsafe { &*core::ptr::from_ref(self).cast::<u8>() })
    }
}
impl Buf for u16 {}
impl Buf for i16 {}
impl Buf for u32 {}
impl Buf for i32 {}
impl Buf for f32 {}
impl Buf for f64 {}

While this is something that could be implemented in cpal, I really see no reason for it.

[Ralith]

Yes, this is completely out of scope for cpal, Use something like the above, or the bytemuck crate.